CWRU PAT Coffee Agenda

Mondays 13:00 - 14:00 | Tuesdays 10:30 - 11:30 | Fridays 11:00 - 12:00

Showing votes from 2018-01-23 11:30 to 2018-01-26 12:00 | Next meeting is Friday Jan 26th, 11:00 am.


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  • Elemental gas-phase abundances of intermediate redshift type Ia supernova star-forming host galaxies.- [PDF] - [Article]

    M.E. Moreno-Raya, L. Galbany, A. R. López-Sánchez, M. Mollá, S. González-Gaitán, J.M. Vílchez, A. Carnero

    The maximum luminosity of type Ia supernovae (SNe Ia) depends on the oxygen abundance of the regions of the host galaxies where they explode. This metallicity dependence reduces the dispersion in the Hubble diagram (HD) when included with the traditional two-parameter calibration of SN Ia light-curve (LC) parameters and absolute magnitude. In this work, we use empirical calibrations to carefully estimate the oxygen abundance of galaxies hosting SNe Ia from the SDSS-II/SNe Survey at intermediate redshift, by measuring their emission line intensities. We also derive electronic temperature with the direct method for a small fraction of objects for consistency. We find a trend of decreasing oxygen abundance with increasing redshift for the most massive galaxies. Moreover, we study the dependence of the HD residuals (HR) with galaxy oxygen abundance obtaining a correlation in line with those found in other works. In particular, the HR vs oxygen abundance shows a slope of -0.186$\pm$0.123 mag dex$^{-1}$ (1.52$\sigma$), in good agreement with theoretical expectations. This implies smaller distance modulii after corrections for SNe Ia in metal-rich galaxies. Based on our previous results on local SNe Ia, we propose this dependence to be due to the lower luminosity of the SNe Ia produced in more metal-rich environments.

  • Optimal identification of HII regions during reionization in 21-cm observations.- [PDF] - [Article]

    Sambit K. Giri, Garrelt Mellema, Raghunath Ghara

    The ability of the future SKA-Low radio telescope to produce tomographic images of the redshifted 21-cm signal will enable direct studies of the evolution of the sizes and shapes of ionized regions during the Epoch of Reionization. However, a reliable identification of ionized regions in noisy interferometric data is not trivial. Here, we introduce an image processing method known as superpixels for this purpose. We compare this method with two other previously proposed ones, one relying on a chosen threshold and the other employing automatic threshold determination using the K-Means algorithm. We use a correlation test and compare power spectra and the bubble size distributions to show that the superpixels method provides a better identificationof ionized regions, especially in the case of noisy data. We also describe some possible additional applications of the superpixel method, namely the derivation of the ionization history and constraints on the source properties in specific regions.

  • Probing galaxy assembly bias with LRG weak lensing observations.- [PDF] - [Article]

    A. Niemiec, E. Jullo, A. D. Montero-Dorta, F. Prada, S. Rodriguez-Torres, E. Perez, A. Klypin, T. Erben, M. Makler, B. Moraes, M. E. S. Pereira, H. Shan

    In Montero-Dorta et al. 2017, we show that luminous red galaxies (LRGs) from the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS) at $z\sim0.55$ can be divided into two groups based on their star formation histories. So-called fast-growing LRGs assemble $80\%$ of their stellar mass at $z\sim5$, whereas slow-growing LRGs reach the same evolutionary state at $z\sim1.5$. We further demonstrate that these two subpopulations present significantly different clustering properties on scales of $\sim1 - 30 \mathrm{Mpc}$. Here, we measure the mean halo mass of each subsample using the galaxy-galaxy lensing technique, in the $\sim190\deg^2$ overlap of the LRG catalogue and the CS82 and CFHTLenS shear catalogues. We show that fast- and slow-growing LRGs have similar lensing profiles, which implies that they live in haloes of similar mass: $\log\left(M_{\rm halo}^{\rm fast}/h^{-1}\mathrm{M}_{\odot}\right) = 12.85^{+0.16}_{-0.26}$ and $\log\left(M_{\rm halo}^{\rm slow}/h^{-1}\mathrm{M}_{\odot}\right) =12.92^{+0.16}_{-0.22}$. This result, combined with the clustering difference, suggests the existence of galaxy assembly bias, although the effect is too subtle to be definitively proven given the errors on our current weak-lensing measurement. We show that this can soon be achieved with upcoming surveys like DES.

  • X-ray and SZ constraints on the properties of hot CGM.- [PDF] - [Article]

    Priyanka Singh, Subhabrata Majumdar, Biman B. Nath, Joseph Silk

    We use observations of stacked X-ray luminosity and Sunyaev-Zel'dovich (SZ) signal from a cosmological sample of $\sim 80,000$ and $104,000$ massive galaxies, respectively, with $ 10^{12.6}\lesssim M_{500} \lesssim 10^{13} M_{\odot}$ and mean redshift, \={z} $\sim$ 0.1 - 0.14 to constrain the hot Circumgalactic Medium (CGM) density and temperature. The X-ray luminosities constrain the density and hot CGM mass, while the SZ signal helps in breaking the density-temperature degeneracy. We consider a simple power-law density distribution ($n_e \propto r^{-3\beta}$) as well as a hydrostatic hot halo model, with the gas assumed to be isothermal in both cases. The datasets are best described by the mean hot CGM profile $\propto r^{-1.2}$, which is shallower than an NFW profile. For halo virial mass $\sim 10^{12}$ - $10^{13} M_{\odot}$, the hot CGM contains $\sim$ 20 - 30\% of galactic baryonic mass for the power-law model and 4 - 11\% for the hydrostatic halo model, within the virial radii. For the power-law model, the hot CGM profile broadly agrees with observations of the Milky Way. The mean hot CGM mass is comparable to or larger than the mass contained in other phases of the CGM for $L^*$ galaxies.

  • Cored density profiles in the DARKexp model.- [PDF] - [Article]

    Claudio Destri

    The DARKexp model represents a novel and promising attempt to solve a long standing problem of statistical mechanics, that of explaining from first principles the quasi--stationary states at the end of the collisionless gravitational collapse. The model, which yields good fits to observation and simulation data on several scales, was originally conceived to provide a theoretical basis for the $1/r$ cusp of the Navarro--Frenk--White profile. In this note we show that it also allows for cored density profiles that, when viewed in three dimensions, in the $r\to0$ limit have the conical shape characteristic of the Burkert profile. It remains to be established whether both cusps and cores, or only one of the two types, are allowed beyond the asymptotic analysis of this work

  • Workshop 8: Supernovae.- [PDF] - [Article]

    Maximilian Stritzinger, Takashi Moriya

    This contribution presents the results of workshop 8 (supernovae) held during the IAU Symposium 339 "Southern Horizons in Time-Domain Astronomy" at Stellenbosch University, South Africa.Workshop 8 covered a cornucopia of topics with each one having a short presentation by a pre-determined participant followed by a round table discussion. During the first of two sessions, G. Hosseinzadeh and H. Kuncarayakti presented results of their recent works on interacting supernovae. This includes both the intriguing Type~Ibn supernova subclass, as well as SN 2017dio, which appears to be the first Type~Ic supernova to exhibit signatures of hydrogen-rich circumstellar interaction at all phases. During the second session, M. Sullivan provided an excellent summary related to the future of transient science in the era of Big Data, and the participants discussed strategies to determine which targets and fields should be selected for spectroscopic followup. Workshop 8 concluded with a rather heated discussion regarding the need for the IAU supernova working group to consider to modify the current criteria for a confirmed supernova to receive an official IAU designation.

  • Role of primordial black holes in the direct collapse scenario of supermassive black hole formation at high redshifts.- [PDF] - [Article]

    Kanhaiya L. Pandey, A. Mangalam

    In this paper, we explore the possibility of accreting primordial black holes as the source of heating for the collapsing gas in the context of the direct collapse black hole scenario for the formation of super-massive black holes (SMBHs) at high redshifts, $z\sim 6-7$. One of the essential requirements for the direct collapse model to work is to maintain the temperature of the in falling gas at $\approx 10^4$ K. We show that even under the existing abundance limits, the primordial black holes of masses $\gtrsim 10^{-2} \ {\rm M}_\odot$, can heat the collapsing gas to an extent that the ${\rm H}_2$ formation is inhibited. The collapsing gas can maintain its temperature at $10^4$ K till the gas reaches a critical density $n_{crit} \approx 10^3$ cm$^{-3}$, at which the roto-vibrational states of ${\rm H}_2$ approaches local thermodynamic equilibrium and ${\rm H}_2$ cooling becomes inefficient. In the absence of ${\rm H}_2$ cooling the temperature of the collapsing gas stays at $\approx 10^4$ K even as it collapses further. We discuss scenarios of subsequent angular momentum removal and the route to find collapse through either a supermassive star or a supermassive disk.

  • Gravitational wave speed: Implications for models without a mass scale.- [PDF] - [Article]

    Henrik Nersisyan, Nelson A. Lima, Luca Amendola

    The recent report that the gravitational wave speed equals the light speed puts strong constraints on the anisotropic stress parameter of many modified gravity models, a quantity that is directly observable through large-scale structure. We show here that models without a mass scale completely escape these constraints. We discuss a few relevant cases in detail: Brans-Dicke theory, nonlocal models, and Galileon Lagrangian.

  • Doppler magnification in flux-limited galaxy number counts with finite redshift bin width.- [PDF] - [Article]

    Song Chen

    In this paper, I investigated the Doppler magnification effect in the flux-limited galaxy number counts with finite redshift bin width. In contradiction with our intuition, the number counts correction formula for different redshift bin are different. For the redshift window as delta function and constant function, the correction formulas have been derived analytically in this paper. These two windows correspond to two extreme cases(i.e. extremely narrow bin and extremely broad bin). An simulation have been implemented to test these formulas. The simulation results indicate the perturbation changes smoothly from one extreme case to another while extending the redshift bin width from half bin width $0.05$ to $0.4$. As a result, Doppler magnification caused number counts perturbation of finite redshift bin width can NOT be compute via redshift integration of the perturbation formula derived with delta function redshift window. It is only a good approximation when the bin width is small. These results are important for galaxy redshift survey kinematic dipole estimation, and meaningful for the relativistic galaxy number counts angular power spectrum estimation, such as CLASSgal and CAMB source.

  • Fine-Tuning, Complexity, and Life in the Multiverse.- [PDF] - [Article]

    Mario Livio, Las Vegas), Martin J. Rees, University of Cambridge)

    The physical processes that determine the properties of our everyday world, and of the wider cosmos, are determined by some key numbers: the 'constants' of micro-physics and the parameters that describe the expanding universe in which we have emerged. We identify various steps in the emergence of stars, planets and life that are dependent on these fundamental numbers, and explore how these steps might have been changed, or completely prevented, if the numbers were different. We then outline some cosmological models where physical reality is vastly more extensive than the 'universe' that astronomers observe (perhaps even involving many 'big bangs'), which could perhaps encompass domains governed by different physics. Although the concept of a multiverse is still speculative, we argue that attempts to determine whether it exists constitute a genuinely scientific endeavor. If we indeed inhabit a multiverse, then we may have to accept that there can be no explanation other than anthropic reasoning for some features our world.

  • Most probable small field inflationary potentials.- [PDF] - [Article]

    Ira Wolfson, Ram Brustein

    Inflationary potentials, with small field excursions, described by a 6th degree polynomial are studied. We solve the Mukhanov-Sasaki equations exactly and employ a probabilistic approach as well as multinomial fitting to analyse the results. We identify leading candidates which yield a tensor-to-scalar ratio $r=0.01$ in addition to currently allowed Cosmic Microwave Background (CMB) spectrum, and observables. Additionally, we find a significant inter-dependence of CMB observables in these models. This might be an important effect for future analyses, since the different moments of the primordial power spectrum are taken to independent in the usual Markov chain Monte Carlo methods.

  • Cospatial Star Formation and Supermassive Black Hole Growth in $z \sim 3$ Galaxies: Evidence for In-situ Co-evolution.- [PDF] - [Article]

    W. Rujopakarn, K. Nyland, G. H. Rieke, G. Barro, D. Elbaz, R. J. Ivison, P. Jagannathan, J. D. Silverman, V. Smolcic, T. Wang

    We present a sub-kpc localization of the sites of supermassive black hole (SMBH) growth in three active galactic nuclei (AGN) at $z \sim 3$ in relation to the regions of intense star formation in their hosts. These AGNs are selected from Karl G. Jansky Very Large Array (VLA) and Atacama Large Millimeter/submillimeter Array (ALMA) observations in the HUDF and COSMOS, with the centimetric radio emission tracing both star formation and AGN, and the sub/millimeter emission by dust tracing nearly pure star formation. We require radio emission to be $\geqslant5\times$ more luminous than the level associated with the sub/millimeter star formation to ensure that the radio emission is AGN-dominated, thereby allowing localization of the AGN and star formation independently. In all three galaxies, the AGN are located within the compact regions of gas-rich, heavily obscured, intense nuclear star formation, with $R_e = 0.4-1.1$ kpc and average star formation rates of $\simeq100-1200$ $M_\odot$yr$^{-1}$. If the current episode of star formation continues at such a rate over the stellar mass doubling time of their hosts, $\simeq 0.2$ Gyr, the newly formed stellar mass will be of the order of $10^{11}$ $M_\odot$ within the central kpc region, concurrently and cospatially with significant growth of the SMBH. This is consistent with a picture of in-situ galactic bulge and SMBH formation. This work demonstrates the unique complementarity of VLA and ALMA observations to unambiguously pinpoint the locations of AGN and star formation down to $\simeq30$ mas, corresponding to $\simeq 230$ pc at $z = 3$.

  • Metastable Dark Energy with Radioactive-like Decay.- [PDF] - [Article] - [UPDATED]

    Arman Shafieloo, Dhiraj Kumar Hazra, Varun Sahni, Alexei A. Starobinsky

    We propose a new class of metastable dark energy (DE) phenomenological models in which the DE decay rate does not depend on external parameters such as the scale factor or the curvature of the Universe. Instead, the DE decay rate is assumed to be a constant depending only on intrinsic properties of DE and the type of a decay channel, similar to case of the radioactive decay of unstable particles and nuclei. As a consequence, the DE energy density becomes a function of the proper time elapsed since its formation, presumably in the very early Universe. Such a natural type of DE decay can profoundly affect the expansion history of the Universe and its age. Metastable DE can decay in three distinct ways: (i) exponentially, (ii) into dark matter, (iii) into dark radiation. Testing metastable DE models with observational data we find that the decay half-life must be many times larger than the age of the Universe. Models in which dark energy decays into dark matter lead to lower values of the Hubble parameter at large redshifts relative to $\Lambda$CDM. Consequently these models provide a better fit to cosmological BAO data (especially data from from high redshift quasars) than concordance ($\Lambda$CDM) cosmology.

  • Intrinsic Alignment in redMaPPer clusters -- II. Radial alignment of satellites toward cluster centers.- [PDF] - [Article] - [UPDATED]

    Hung-Jin Huang, Rachel Mandelbaum, Peter E. Freeman, Yen-Chi Chen, Eduardo Rozo, Eli Rykoff

    We study the orientations of satellite galaxies in redMaPPer clusters constructed from the Sloan Digital Sky Survey at $0.1<z<0.35$ to determine whether there is any preferential tendency for satellites to point radially toward cluster centers. We analyze the satellite alignment (SA) signal based on three shape measurement methods (re-Gaussianization, de Vaucouleurs, and isophotal shapes), which trace galaxy light profiles at different radii. The measured SA signal depends on these shape measurement methods. We detect the strongest SA signal in isophotal shapes, followed by de Vaucouleurs shapes. While no net SA signal is detected using re-Gaussianization shapes across the entire sample, the observed SA signal reaches a statistically significant level when limiting to a subsample of higher luminosity satellites. We further investigate the impact of noise, systematics, and real physical isophotal twisting effects in the comparison between the SA signal detected via different shape measurement methods. Unlike previous studies, which only consider the dependence of SA on a few parameters, here we explore a total of 17 galaxy and cluster properties, using a statistical model averaging technique to naturally account for parameter correlations and identify significant SA predictors. We find that the measured SA signal is strongest for satellites with the following characteristics: higher luminosity, smaller distance to the cluster center, rounder in shape, higher bulge fraction, and distributed preferentially along the major axis directions of their centrals. Finally, we provide physical explanations for the identified dependences, and discuss the connection to theories of SA.

  • Precise Time Delays from Strongly Gravitationally Lensed Type Ia Supernovae with Chromatically Microlensed Images.- [PDF] - [Article] - [UPDATED]

    Daniel A. Goldstein, Peter E. Nugent, Daniel N. Kasen, Thomas E. Collett

    Time delays between the multiple images of strongly lensed Type Ia supernovae (gl\sneia) have the potential to deliver precise cosmological constraints, but the effects of microlensing on the measurement have not been studied in detail. Here we quantify the effect of microlensing on the gl\snia\ yield of the Large Synoptic Survey Telescope (LSST) and the effect of microlensing on the precision and accuracy of time delays that can be extracted from LSST gl\sneia. Microlensing has a negligible effect on the LSST gl\snia\ yield, but it can be increased by a factor of $\sim$2 to 930 systems using a novel photometric identification technique based on spectral template fitting. Crucially, the microlensing of gl\sneia\ is achromatic until 3 rest-frame weeks after the explosion, making the early-time color curves microlensing-insensitive time delay indicators. By fitting simulated flux and color observations of microlensed gl\sneia\ with their underlying, unlensed spectral templates, we forecast the distribution of absolute time delay error due to microlensing for LSST, which is unbiased at the sub-percent level and peaked at 1\% for color curve observations in the achromatic phase, while for light curve observations it is comparable to state-of-the-art mass modeling uncertainties (4\%). About 70\% of LSST gl\snia\ images should be discovered during the achromatic phase, indicating that microlensing time delay uncertainties can be minimized if prompt multicolor follow-up observations are obtained. Accounting for microlensing, the 1--2 day time delay on the recently discovered gl\snia\ iPTF16geu can be measured to 40\% precision, limiting its cosmological utility.

  • Relativistic Astronomy.- [PDF] - [Article] - [UPDATED]

    Bing Zhang, Kunyang Li

    The "Breakthrough Starshot" aims at sending near-speed-of-light cameras to nearby stellar systems in the future. Due to the relativistic effects, a trans-relativistic camera naturally serves as a spectrograph, a lens, and a wide-field camera. We demonstrate this through a simulation of the optical-band image of the nearby galaxy M51 in the rest frame of the trans-relativistic camera. We suggest that observing celestial objects using a trans-relativistic camera may allow one to study the astronomical objects in a special way, and to perform unique tests on the principles of special relativity. We outline several examples that trans-relativistic cameras may make important contributions to astrophysics and suggest that the Breakthrough Starshot cameras may be launched in any direction to serve as a unique astronomical observatory.

  • Shaken Snow Globes: Kinematic Tracers of the Multiphase Condensation Cascade in Massive Galaxies, Groups, and Clusters.- [PDF] - [Article] - [UPDATED]

    M. Gaspari, M. McDonald, S. L. Hamer, F. Brighenti, P. Temi, M. Gendron-Marsolais, J. Hlavacek-Larrondo, A. C. Edge, N. Werner, P. Tozzi, M. Sun, J. M. Stone, G. R. Tremblay, M. T. Hogan, D. Eckert, S. Ettori, H. Yu, V. Biffi, S. Planelles

    We propose a novel method to constrain turbulence and bulk motions in massive galaxies, groups and clusters, exploring both simulations and observations. As emerged in the recent picture of the top-down multiphase condensation, the hot gaseous halos are tightly linked to all other phases in terms of cospatiality and thermodynamics. While hot halos (10^7 K) are perturbed by subsonic turbulence, warm (10^4 K) ionized and neutral filaments condense out of the turbulent eddies. The peaks condense into cold molecular clouds (< 100 K) raining in the core via chaotic cold accretion (CCA). We show all phases are tightly linked via the ensemble (wide-aperture) velocity dispersion along the line of sight. The correlation arises in complementary long-term AGN feedback simulations and high-resolution CCA runs, and is corroborated by the combined Hitomi and new IFU measurements in Perseus cluster. The ensemble multiphase gas distributions are characterized by substantial spectral line broadening (100-200 km/s) with mild line shift. On the other hand, pencil-beam detections sample the small-scale clouds displaying smaller broadening and significant line shift up to several 100 km/s, with increased scatter due to the turbulence intermittency. We present new ensemble sigma_v of the warm Halpha+[NII] gas in 72 observed cluster/group cores: the constraints are consistent with the simulations and can be used as robust proxies for the turbulent velocities, in particular for the challenging hot plasma (otherwise requiring extremely long X-ray exposures). We show the physically motivated criterion C = t_cool/_teddy ~ 1 best traces the condensation extent region and presence of multiphase gas in observed clusters/groups. The ensemble method can be applied to many available datasets and can substantially advance our understanding of multiphase halos in light of the next-generation multiwavelength missions.

  • The Effect of Anisotropic Extra Dimension in Cosmology.- [PDF] - [Article] - [UPDATED]

    Seyen Kouwn, Phillial Oh, Chan-Gyung Park

    We consider five dimensional conformal gravity theory which describes an anisotropic extra dimension. Reducing the theory to four dimensions yields Brans-Dicke theory with a potential and a hidden parameter $z$ which implements the anisotropy between the four dimensional spacetime and the extra dimension. We find that a range of value of the parameter $z$ can address the current dark energy density compared to the Planck energy density. Constraining the parameter $z$ and the other cosmological model parameters using the recent observational data consisting of the Hubble parameters, type Ia supernovae, and baryon acoustic oscillations, together with the Planck or WMAP 9-year data of the cosmic microwave background radiation, we find $z>-2.05$ for Planck data and $z>-2.09$ for WMAP 9-year data at 95\% confidence level. We also obtained constraints on the rate of change of the effective Newtonian constant~($G_{\rm eff}$) at present and the variation of $G_{\rm eff}$ since the epoch of recombination to be consistent with observation.

  • GW170817 Falsifies Dark Matter Emulators.- [PDF] - [Article] - [UPDATED]

    Sibel Boran, Shantanu Desai, Emre Kahya, Richard Woodard

    On August 17, 2017 the LIGO interferometers detected the gravitational wave (GW) signal (GW170817) from the coalescence of binary neutron stars. This signal was also simultaneously seen throughout the electromagnetic (EM) spectrum from radio waves to gamma-rays. We point out that this simultaneous detection of GW and EM signals rules out a class of modified gravity theories, termed ``dark matter emulators,'' which dispense with the need for dark matter by making ordinary matter couple to a different metric from that of GW. We discuss other kinds of modified gravity theories which dispense with the need for dark matter and are still viable. This simultaneous observation also provides the first observational test of Einstein's Weak Equivalence Principle (WEP) between gravitons and photons. We estimate the Shapiro time delay due to the gravitational potential of the total dark matter distribution along the line of sight (complementary to the calculation in arXiv:1710.05834) to be about 400 days. Using this estimate for the Shapiro delay and from the time difference of 1.7 seconds between the GW signal and gamma-rays, we can constrain violations of WEP using the parameterized post-Newtonian (PPN) parameter $\gamma$, and is given by $|\gamma_{\rm {GW}}-\gamma_{\rm{EM}}|<9.8 \times 10^{-8}$.

  • Observational signatures of the parametric amplification of gravitational waves during reheating after inflation.- [PDF] - [Article] - [UPDATED]

    Sachiko Kuroyanagi, Chunshan Lin, Misao Sasaki, Shinji Tsujikawa

    We study the evolution of Gravitational Waves (GWs) during and after inflation as well as the resulting observational consequences in a Lorentz-violating massive gravity theory with one scalar (inflaton) and two tensor degrees of freedom. We consider two explicit examples of the tensor mass $m_g$ that depends either on the inflaton field $\phi$ or on its time derivative $\dot{\phi}$, both of which lead to parametric excitations of GWs during reheating after inflation. The first example is Starobinsky's $R^2$ inflation model with a $\phi$-dependent $m_g$ and the second is a low-energy-scale inflation model with a $\dot{\phi}$-dependent $m_g$. We compute the energy density spectrum $\Omega_{\rm GW}(k)$ today of the GW background. In the Starobinsky's model, we show that the GWs can be amplified up to the detectable ranges of both CMB and DECIGO, but the bound from the big bang nucleosynthesis is quite tight to limit the growth. In low-scale inflation with a fast transition to the reheating stage driven by the potential $V(\phi)=M^2 \phi^2/2$ around $\phi \approx M_{\rm pl}$ (where $M_{\rm pl}$ is the reduced Planck mass), we find that the peak position of $\Omega_{\rm GW}(k)$ induced by the parametric resonance can reach the sensitivity region of advanced LIGO for the Hubble parameter of order 1 GeV at the end of inflation. Thus, our massive gravity scenario offers exciting possibilities for probing the physics of primordial GWs at various different frequencies.

  • The Hubble constant from SN Refsdal.- [PDF] - [Article] - [UPDATED]

    J. Vega-Ferrero, J. M. Diego, V. Miranda, G. M. Bernstein

    Hubble Space Telescope observations from December 11 2015 detected the expected fifth counter image of SN Refsdal at $z = 1.49$. In this letter, we compare the time delay predictions from numerous models with the measured value derived by \citet{Kelly2016a} from very early data in the light curve of the SN Refsdal, and find a best value for $H_0 = 64^{+9}_{-11}~\mathrm{km~s^{-1}~Mpc^{-1}}$ (68\% CL), in excellent agreement with predictions from CMB and recent weak lensing data + BAO + BBN (from the DES Collaboration). This is the first constraint on $H_0$ derived from time delays between multiple lensed SN images, and the first with a galaxy cluster lens, so subject to systematic effects different from other time-delay $H_0$ estimates. Additional time delay measurements from new multiply-imaged SNe will allow derivation of competitive constraints on $H_0$.

  • The gravitational-wave luminosity distance in modified gravity theories.- [PDF] - [Article] - [UPDATED]

    Enis Belgacem, Yves Dirian, Stefano Foffa, Michele Maggiore

    In modified gravity the propagation of gravitational waves (GWs) is in general different from that in general relativity. As a result, the luminosity distance for GWs can differ from that for electromagnetic signals, and is affected both by the dark energy equation of state $w_{\rm DE}(z)$ and by a function $\delta(z)$ describing modified propagation. We show that, once Bayesian parameter estimation in the modified gravity model is taken into account, the effect of $w_{\rm DE}(z)$ is suppressed. This implies that existing estimates of the sensitivity to $w_{\rm DE}(z)$ of LISA or of third-generation GW interferometers such as the Einstein Telescope (ET) are overestimated, by about one order of magnitude. On the other hand, the effect of $\delta(z)$ is not compensated by parameter estimation and is the dominant one. We illustrate this using a nonlocal modification of gravity, that has been shown to fit remarkably well CMB, SNe, BAO and structure formation data, and we discuss the prospects for distinguishing nonlocal gravity from $\Lambda$CDM with ET. We find that, depending on the exact sensitivity, a few tens of standard sirens with measured redshift at $z\sim 0.4$, or a few hundreds at $1< z < 2$, could suffice.

  • Primordial Black Holes from Polynomial Potentials in Single Field Inflation.- [PDF] - [Article] - [UPDATED]

    Mark P. Hertzberg, Masaki Yamada

    Within canonical single field inflation models, we provide a method to reverse engineer and reconstruct the inflaton potential from a given power spectrum. This is not only a useful tool to find a potential from observational constraints, but also gives insight into how to generate a large amplitude spike in density perturbations, especially those that may lead to primordial black holes (PBHs). In accord with other works, we find that the usual slow-roll conditions need to be violated in order to generate a significant spike in the spectrum. We find that a way to achieve a very large amplitude spike in single field models is for the classical roll of the inflaton to over-shoot a local minimum during inflation. We provide an example of a quintic polynomial potential that implements this idea and leads to the observed spectral index, observed amplitude of fluctuations on large scales, significant PBH formation on small scales, and is compatible with other observational constraints. We quantify how much fine-tuning is required to achieve this in a family of random polynomial potentials, which may be useful to estimate the probability of PBH formation in the string landscape.

  • Reconstructing warm inflation.- [PDF] - [Article] - [UPDATED]

    Ramon Herrera

    The reconstruction of a warm inflationary universe model from the scalar spectral index $n_S(N)$ and the tensor to scalar ratio $r(N)$ as a function of the number of e-folds $N$ is studied. Under a general formalism we find the effective potential and the dissipative coefficient in terms of the cosmological parameters $n_S$ and $r$ considering the weak and strong dissipative stages under the slow roll approximation. As a specific example, we study the attractors for the index $n_S$ given by $n_{S}-1\propto N^{-1}$ and for the ratio $r\propto N^{-2}$, in order to reconstruct the model of warm inflation. Here, expressions for the effective potential $V(\phi)$ and the dissipation coefficient $\Gamma(\phi)$ are obtained.

  • Collisions in Primordial Star Clusters: Formation Pathway for intermediate mass black holes.- [PDF] - [Article] - [UPDATED]

    B. Reinoso, D.R.G. Schleicher, M. Fellhauer, R.S. Klessen, T.C.N. Boekholt

    Collisions were suggested to potentially play a role in the formation of massive stars in present day clusters, and have likely been relevant during the formation of massive stars and intermediate mass black holes within the first star clusters. In the early Universe, the first stellar clusters were particularly dense, as fragmentation typically only occurred at densities above $10^9$cm$^{-3}$, and the radii of the protostars were enhanced due to the larger accretion rates, suggesting a potentially more relevant role of stellar collisions. We present here a detailed parameter study to assess how the number of collisions as well as the mass growth of the most massive object depends on the properties of the cluster, and we characterize the time evolution with three effective parameters, the time when most collisions occur, the duration of the collisions period, as well as the normalization required to obtain the total number of collisions. We apply our results to typical Population III (Pop.III) clusters of about $1000$M$_\odot$, finding that a moderate enhancement of the mass of the most massive star by a factor of a few can be expected. For more massive Pop.III clusters as expected in the first atomic cooling halos, we expect a more significant enhancement by a factor of $15-32$. We therefore conclude that collisions in massive Pop.III clusters were likely relevant to form the first intermediate mass black holes.


  • Self-interacting dark matter constraints in a thick dark disk scenario.- [PDF] - [Article]

    Kyriakos Vattis, Savvas M. Koushiappas

    A thick dark matter disk is predicted in cold dark matter simulations as the outcome of the interaction between accreted satellites and the stellar disk in Milky Way sized halos. We study the effects of a self-interacting thick dark disk on the energetic neutrino flux from the Sun. We find that for particle masses between 100 GeV and 1 TeV and dark matter annihilation to heavy leptons either the self-interaction may not be strong enough to solve the small scale structure motivation or a dark disk cannot be present in the Milky Way.

  • Fast radio bursts' recipes for the distributions of dispersion measures, flux densities, and fluences.- [PDF] - [Article]

    Yuu Niino

    We investigate how the statistical properties of dispersion measure (DM) and apparent flux density/fluence of (non-repeating) fast radio bursts (FRBs) are determined by unknown cosmic rate density history [$\rhoFRB (z)$] and luminosity function (LF) of the transient events. We predict the distributions of DMs, flux densities, and fluences of FRBs taking account of the variation of the receiver efficiency within its beam, using analytical models of $\rhoFRB (z)$ and LF. Comparing the predictions with the observations, we show that the cumulative distribution of apparent fluences suggests that FRBs originate at cosmological distances and $\rhoFRB$ increases with redshift resembling cosmic star formation history (CSFH). We also show that a LF model with a bright-end cutoff at log$_{10}L_\nu$ [erg s$^{-1}$Hz$^{-1}$] $\sim$ 34 are favored to reproduce the observed DM distribution if $\rhoFRB (z)\propto$ CSFH, although the statistical significance of the constraints obtained with the current size of the observed sample is not high. Finally, we find that the correlation between DM and flux density of FRBs is potentially a powerful tool to distinguish whether FRBs are at cosmological distances or in the local universe more robustly with future observations.

  • Internal Plateau in Short GBRs and Quark Stars.- [PDF] - [Article]

    A. Li

    I summarize our recent calculations on quark stars (QSs), for the purpose of explaining some short gamma-ray bursts characterized by internal plateau in their early X-ray afterglow. According to the present plateau sample, the QS central engine model is demonstrated to more preferred than the original neutron star (NS) one. New QS equation of states (PMQS1, PMQS2, PMQS3) are then proposed, respecting fully the observed burst data and the mass distribution of the Galactic NS-NS systems.

  • The Radio and $\gamma$-ray Variability Analysis of S5 0716+714.- [PDF] - [Article]

    H. Z. Li, Y. G. Jiang, T. F. Yi, D. F. Guo, X. Chen, H. M. Zhang, Q. G. Gao, F. W. Lu, J. Y. Ren

    We have studied the variability of \object{S5 0716+714} at radio 15 GHz and $\gamma$-ray band using three different methods. A possible periodicity of $P_{15 GHz}=266.0\pm11.5$ and $P_{\gamma}=344.0\pm16.4$ days are obtained for radio 15 GHz and $\gamma$-ray light curves, respectively. The variability may be related to the intrinsically emission mechanism. The difference between the variability timescales of radio 15 GHz and $\gamma$-ray may be due to that the emission of radio 15 GHz is produced via the synchrotron process, while the $\gamma$-ray is produced by both the SSC and EC processes.

  • Optical/infrared polarised emission in X-ray binaries.- [PDF] - [Article]

    David M. Russell

    Recently, evidence for synchrotron emission in both black hole and neutron star X-ray binaries has been mounting, from optical/infrared spectral, polarimetric, and fast timing signatures. The synchrotron emission of jets can be highly linearly polarised, depending on the configuration of the magnetic field. Optical and infrared (OIR) polarimetric observations of X-ray binaries are presented in this brief review. The OIR polarimetric signature of relativistic jets is detected at levels of ~ 1-10 %, similar to AGN cores. This reveals that the magnetic geometry in the compact jets may be similar for supermassive and stellar-mass BHs. The magnetic fields near the jet base in most of these systems appear to be turbulent, variable and on average, aligned with the jet axis, although there are some exceptions. These measurements probe the physical conditions in the accretion (out)flow and demonstrate a new way of connecting inflow and outflow, using both rapid timing and polarisation. Variations in polarisation could be due to rapid changes of the ordering of the magnetic field in the emitting region, or in one case, flares from individual ejections or collisions between ejecta. It is predicted that in some cases, variable levels of X-ray polarisation from synchrotron emission originating in jets will be detected from accreting Galactic black holes with upcoming spaceborne X-ray polarimeters.

  • Search for Ultra-High Energy WIMPs by detecting neutrino signatures from the earth core.- [PDF] - [Article]

    Ye Xu

    I study the possibility of probing Ultra-High Energy (UHE from now on) dark matter particles (>10$^8$ GeV) due to the decay of superheavy dark matter via detection of UHE neutrino signatures from the earth core. The UHE WIMP event rates are estimated at the energies of 100 PeV, and 1 EeV, 10 EeV, 100 EeV and 1 ZeV in JEM-EUSO and at the energy of 1 ZeV in IceCube, respectively. The diffuse neutrino contaminations are also roughly estimated in JEM-EUSO and IceCube. I found that the extreme energy WIMPs can be detected by JEM-EUSO above 1 EeV and by IceCube above 1 ZeV in the $\chi$ mass range of 10GeV-200GeV.

  • Combined Constraints on the Equation of State of Dense Neutron-Rich Matter from Terrestrial Experiments and Observations of Neutron Stars.- [PDF] - [Article]

    Nai-Bo Zhang, Bao-An Li, Jun Xu

    Within the parameter space of equation of state (EOS) of dense neutron-rich matter limited by existing constraints mainly from terrestrial nuclear experiments, we investigate how the neutron star maximum mass $M_{\rm{max}}>2.01\pm0.04$ M$_\odot$, radius $10.62<R_{\rm{1.4}}< 12.83$ km and tidal deformability $\Lambda_{1.4}\leq800$ of canonical neutron stars all together constrain the EOS of dense neutron-rich nucleonic matter. While the 3-D parameter space of $K_{\rm{sym}}$ (curvature of nuclear symmetry energy), $J_{\rm{sym}}$ and $J_0$ (skewness of the symmetry energy and EOS of symmetric nuclear matter (SNM), respectively) are narrowed down significantly by the observational constraints, more data are needed to pin down the individual values of $K_{\rm{sym}}$, $J_{\rm{sym}}$ and $J_0$. The $J_0$ largely controls the maximum mass of neutron stars. While the EOS with $J_0=0$ is sufficiently stiff to support neutron stars as massive as 2.37 M$_{\odot}$, to support the ones as massive as 2.74 M$_{\odot}$ (composite mass of GW170817) requires $J_0$ to be larger than its currently known maximum value of about 400 MeV. The upper limit on the tidal deformability of $\Lambda_{1.4}=800$ from the recent observation of GW170817 is found to provide upper limits on some EOS parameters consistent with but less restrictive than the existing constraints of other observables studied.

  • No Escape from the Supernova! Magnetic Imprisonment of Dusty Pinballs by a Supernova Remnant.- [PDF] - [Article]

    Brian J. Fry, Brian D. Fields, John R. Ellis

    Motivated by recent measurements of deposits of $^{60}$Fe on the ocean floor and the lunar surface, we model the transport of dust grains containing $^{60}$Fe from a near-Earth (i.e., within 100 pc) supernova (SN). We inject dust grains into the environment of a SN remnant (SNR) and trace their trajectories using a magnetohydrodynamic description. We assume the interstellar medium (ISM) magnetic fields are turbulent, and are amplified by the SNR shock, while the SN wind and ejecta fields are negligible. We examine the various influences on the dust grains within the SNR to determine when/if the dust decouples from the plasma, how much it is sputtered, and where within the SNR the dust grains are located. We find that Rayleigh-Taylor instabilities are important for dust survival, as they influence the location of the SN's reverse shock. We find that the presence of a magnetic field within the shocked ISM material limits the passage of SN dust grains, with the field either reflecting or trapping the grains within the heart of the SNR. These results have important implications for {\it in situ} $^{60}$Fe measurements, and for dust evolution in SNRs generally.

  • The jet-ISM interactions in IC 5063.- [PDF] - [Article]

    Dipanjan Mukherjee, Alex Y. Wagner, Geoffrey V. Bicknell, Raffaella Morganti, Tom Oosterloo, Nicole Nesvadba, Ralph S. Sutherland

    The interstellar medium of the radio galaxy IC 5063 is highly perturbed by an AGN jet expanding in the gaseous disc of the galaxy. We model this interaction with relativistic hydrodynamic simulations and multiphase initial conditions for the interstellar medium and compare the results with recent observations. As the jets flood through the inter-cloud channels of the disc, they ablate, accelerate, and disperse clouds to velocities exceeding $400 \mbox{km s}^{-1}$. Clouds are also destroyed or displaced in bulk from the central regions of the galaxy. Our models with jet powers of $10^{44} \mbox{erg s}^{-1}$ and $10^{45} \mbox{erg s}^{-1}$ are capable of reproducing many of the features seen in the position-velocity diagram published in Morganti et al. (2015) and confirm the notion that the jet is responsible for the strongly perturbed gas dynamics seen in the ionized, neutral, and molecular gas phases. In our simulations, we also see strong venting of the jet plasma perpendicular to the disc, which entrains clumps and diffuse filaments into the halo of the galaxy. Our simulations are the first 3D hydrodynamic simulations of the jet and ISM of IC 5063.

  • Relativistic anisotropic stars with the polytropic equation of state in general relativity.- [PDF] - [Article]

    A. A. Isayev

    Spherically symmetric relativistic stars with the polytropic equation of state, which possess the local pressure anisotropy, are considered in the context of general relativity. The modified Lane-Emden equations are derived for the special ansatz for the anisotropy parameter $\Delta$ in the form of the differential relation between $\Delta$ and the metric function $\nu$. The analytical solutions of the obtained equations are found for incompressible fluid stars. The dynamical stability of incompressible anisotropic fluid stars against radial oscillations is studied.

  • Broad-line type Ic Supernova SN 2014ad.- [PDF] - [Article]

    D.K. Sahu, G.C. Anupama, N.K. Chakradhari, S. Srivastav, Masaomi Tanaka, Keiichi Meada, Kenichi Nomoto

    We present optical and ultraviolet photometry, and low resolution optical spectroscopy of the broad-line type Ic supernova SN 2014ad in the galaxy PGC 37625 (Mrk 1309), covering the evolution of the supernova during $-$5 to +87 d with respect to the date of maximum in $B$-band. A late phase spectrum obtained at +340 d is also presented. With an absolute $V$ band magnitude at peak of $M_{V}$ = $-$18.86 $\pm$ 0.23 mag, SN 2014ad is fainter than Gamma Ray Burst (GRB) associated supernovae, and brighter than most of the normal and broad-line type Ic supernovae without an associated GRB. The spectral evolution indicates the expansion velocity of the ejecta, as measured using the Si\,{\sc ii} line, to be as high as $\sim$ 33500 km\,s$^{-1}$ around maximum, while during the post-maximum phase it settles down at $\sim$ 15000 km\,s$^{-1}$. The expansion velocity of SN 2014ad is higher than all other well observed broad-line type Ic supernovae except the GRB associated SN 2010bh. The explosion parameters, determined by applying the Arnett's analytical light curve model to the observed bolometric light curve, indicate that it was an energetic explosion with a kinetic energy of $\sim$ (1 $\pm$ 0.3)$\times$10$^{52}$ ergs, a total ejected mass of $\sim$ (3.3 $\pm$ 0.8) M$_\odot$, and $\sim$ 0.24 M$_\odot$ of $^{56}$Ni was synthesized in the explosion. The metallicity of the host galaxy near the supernova region is estimated to be $\sim$ 0.5 Z$_\odot$.

  • Identify binary extreme-mass-ratio inspirals with multi-band gravitational-wave observations.- [PDF] - [Article]

    Wen-Biao Han, Xian Chen

    A small compact object whirling into a massive black hole (SMBH) of $10^6\,M_\odot$ forms an extreme-mass-ratio inspiral (EMRI). It is one of the most important sources of gravitational waves (GWs) because the waveform contains rich information about the space-time geometry of the SMBH. Recently, we have shown that the small bodies in as many as $10\%$ of the EMRIs could be binary black holes (BBHs). In this Letter we demonstrate that these binary-EMRIs (b-EMRIs) emit both $10^2$ Hz and $10^{-3}$ Hz GWs because the BBHs coalesce into single black holes (BHs) at a distance of ${\cal O}(10)$ gravitational radii from the SMBHs. Since BBH coalescence normally induces a large recoil velocity to the merger remnant, we propose a novel method of detecting b-EMRIs by looking for glitches in the waveforms of EMRIs, induced by the gravitational recoil, and cross-correlating them with LIGO/Virgo events. The detection, in turn, puts stringent constraint on the magnitude and direction of the recoil velocity. The uniqueness of this searching strategy and the potential payback makes b-EMRI an ideal science case for future joint observations using both ground- and space-based GW detectors.

  • Neutrino-nucleon scattering in the neutrino-sphere.- [PDF] - [Article]

    Paulo F. Bedaque, Sanjay Reddy, Srimoyee Sen, Neill C. Warrington

    We calculate the differential scattering rate for thermal neutrinos in a hot and dilute gas of interacting neutrons using linear response theory. The dynamical structure factors for density and spin fluctuations of the strongly interacting neutron matter, expected in the neutrino decoupling regions of supernovae and neutron star mergers, are calculated in the virial expansion for the first time. Correlations due to nucleon-nucleon interactions are taken into account using a pseudo-potential that reproduces measured nucleon-nucleon phase shifts, and we find that attractive s-wave interactions enhance the density response and suppress the spin response of neutron matter. The net effect of neutron correlations is to strongly suppress backscattering. Moreover, we find nearly exact scaling laws for the response functions, valid for the range $T = 5 - 10$ MeV and q < 30 MeV, allowing us to obtain analytic results for the dynamic structure factors at second-order in the fugacity of the neutron gas. We find that the modification of scattering rates depends on the energy and momentum exchanged, implying that dynamical structure factors are essential to describe neutrino decoupling in supernovae and neutron star mergers.

  • Gravitational wave bursts from long gamma-ray bursts.- [PDF] - [Article]

    Antonios Nathanail, Mariafelicia De Laurentis

    One of the most luminous explosions detected, gamma-ray bursts, especially the so-called long-duration bursts, most probably consist of an intrinsic core-collapse to a black hole inside a super massive star. We point out that this collapse alone will give a generic gravitational wave burst. It has been shown that the strength of this burst depends on the dimensionless spin parameter of the collapsing object. Under descent assumptions the gamma-ray burst's central engine powers the explosion electromagnetically due to the rotation of the newly formed black hole. We argue that the peak luminosity and the isotropic energy of the gamma-ray burst can be associated with the spin of the black hole, due to this mechanism. Since, both gravitational and electromagnetic emission depend on the spin, they can be correlated and thus give a straight estimate for the gravitational wave burst, when we have in hand a gamma-ray burst with known distance. We discuss detectability limits for present and future detectors.

  • Hypernuclear stars from relativistic Hartree-Fock density functional theory.- [PDF] - [Article]

    Jia Jie Li, Wen Hui Long, Armen Sedrakian, (2) Lanzhou University, (3) FIAS)

    The hypernuclear matter is studied within the relativistic Hartree-Fock theory employing several parametrizations of the hypernuclear density functional with density dependent couplings. The equations of state and compositions of hypernuclear matter are determined for each parametrization and compact stars are constructed by solving their structure equations in spherical symmetry. We quantify the softening effect of Fock terms on the equation of state, as well as discuss the impact of tensor interactions, which are absent in the Hartree theories. Starting from models of density functionals which are fixed in the nuclear sector to the nuclear phenomenology, we vary the couplings in the hyperonic sector around the central values which are fitted to the hyperon potentials in nuclear matter. We use the SU(6) spin-flavor and SU(3) flavor symmetric quark models to relate the hyperonic couplings to the nucleonic ones. We find, consistent with previous Hartree studies, that for the SU(6) model the maximal masses of compact stars are below the two-solar mass limit. In the SU(3) model we find sufficiently massive compact stars with cores composed predominantly of $\Lambda$ and $\Xi$ hyperons and a low fraction of leptons (mostly electrons). The parameter space of the SU(3) model is identified where simultaneously hypernuclear compact stars obey the astrophysical limits on pulsar masses and the empirical hypernuclear potentials in nuclear matter are reproduced.

  • A Study of Low-Mass X-Ray Binaries in the Low-Luminosity Regime.- [PDF] - [Article]

    E. Sonbas, K. S. Dhuga, E. Gogus

    A recent study of a small sample of X-ray binaries (XRBs) suggests a significant softening of spectra of neutron star (NS) binaries as compared to black hole (BH) binaries in the luminosity range 10$^{34}$ - 10$^{37}$ erg/s. This softening is quantified as an anticorrelation between the spectral index and the 0.5 - 10 keV X-ray luminosity. We extend the study to significantly lower luminosities (i.e., $\sim$ a few $\times$ $10^{30}$ erg/s) for a larger sample of XRBs. We find evidence for a significant anticorrelation between the spectral index and the luminosity for a group of NS binaries in the luminosity range 10$^{32}$ to 10$^{33}$ erg/s. Our analysis suggests a steep slope for the correlation i.e., -2.12 $\pm$ 0.63. In contrast, BH binaries do not exhibit the same behavior. We examine the possible dichotomy between NS and BH binaries in terms of a Comptonization model that assumes a feedback mechanism between an optically thin hot corona and an optically thick cool source of soft photons. We gauge the NS-BH dichotomy by comparing the extracted corona temperatures, Compton-y parameters and the Comptonization amplification factors: The mean temperature of the NS group is found to be significantly lower than the equivalent temperature for the BH group. The extracted Compton-y parameters and the amplification factors follow the theoretically predicted relation with the spectral index.

  • PSR J1618-3921: a recycled pulsar in an eccentric orbit.- [PDF] - [Article]

    F. Octau, I. Cognard, L. Guillemot, T. M. Tauris, P. C. C. Freire, G. Desvignes, G. Theureau

    PSR~J1618$-$3921 is an $11.99$-ms pulsar in a $22.7$-d orbit around a likely low-mass He white dwarf companion, discovered in a survey of the intermediate Galactic latitudes at 1400 MHz conducted with the Parkes radio telescope in the late 1990s. Although PSR~J1618$-$3921 was discovered more than 15 years ago, only limited information has been published about this pulsar which has a surprisingly large orbital eccentricity ($e \simeq 0.027$), considering its high spin frequency and likely small companion mass. The focus of this work is a precise measurement of the spin, astrometric and orbital characteristics of PSR J1618$-$3921. This was done with timing observations made at the Nan\c{c}ay Radio Telescope, from 2009 to 2017. We analyzed the timing data recorded at the Nan\c{c}ay Radio Telescope over several years to characterize the properties of PSR~J1618$-$3921. A rotation ephemeris for this pulsar was obtained by analyzing the times of arrival of the radio pulses at the telescope. We confirm the unusual eccentricity of PSR~J1618$-$3921 and discuss several hypotheses regarding its formation, in the context of other discoveries of recycled pulsars in eccentric orbits.

  • Acceleration of ultrahigh-energy cosmic rays in starburst superwinds.- [PDF] - [Article]

    Luis Alfredo Anchordoqui

    The sources of ultrahigh-energy cosmic rays (UHECRs) have been stubbornly elusive. However, the latest report of the Pierre Auger Observatory provides a compelling indication for a possible correlation between the arrival directions of UHECRs and nearby starburst galaxies. We argue that if starbursts are sources of UHECRs, then particle acceleration in the large-scale terminal shock of the superwind that flows from the starburst engine represents the best known concept model in the market. We investigate new constraints on the model and readjust free parameters accordingly. We show that UHECR acceleration above about 10^{11} GeV remains consistent with observation. We also show that the model could accommodate hard source spectra as required by Auger data.

  • Strong disc winds traced throughout outbursts in black-hole X-ray binaries.- [PDF] - [Article]

    B.E. Tetarenko, J.-P. Lasota, C.O. Heinke, G. Dubus, G.R. Sivakoff

    Recurring outbursts associated with matter flowing onto compact stellar remnants (black-holes, neutron stars, white dwarfs) in close binary systems, provide strong test beds for constraining the poorly understood accretion process. The efficiency of angular momentum (and thus mass) transport in accretion discs, which has traditionally been encoded in the $\alpha$-viscosity parameter, shapes the light-curves of these outbursts. Numerical simulations of the magneto-rotational instability that is believed to be the physical mechanism behind this transport find values of $\alpha \sim 0.1-0.2$ as required from observations of accreting white dwarfs. Equivalent $\alpha$-viscosity parameters have never been estimated in discs around neutron stars or black holes. Here we report the results of an analysis of archival X-ray light-curves of twenty-one black hole X-ray binary outbursts. Applying a Bayesian approach for a model of accretion allows us to determine corresponding $\alpha$-viscosity parameters, directly from the light curves, to be $\alpha \sim$0.2--1. This result may be interpreted either as a strong intrinsic rate of angular momentum transport in the disc, which can only be sustained by the magneto-rotational instability if a large-scale magnetic field threads the disc, or as a direct indication that mass is being lost from the disc through substantial mass outflows strongly shaping the X-ray binary outburst. Furthermore, the lack of correlation between our estimates of $\alpha$-viscosity and accretion state implies that such outflows can remove a significant fraction of disc mass in all black hole X-ray binary accretion states, favouring magnetically-driven winds over thermally-driven winds that require specific radiative conditions.

  • A Three-Dimensional Simulation of a Magnetized Accretion Disk: Fast Funnel Accretion onto a Weakly-Magnetized Star.- [PDF] - [Article]

    Shinsuke Takasao, Kengo Tomida, Kazunari Iwasaki, Takeru K. Suzuki

    We present the results of a global three-dimensional magnetohydrodynamics simulation of an accretion disk with a rotating, weakly magnetized central star. The disk is threaded by a weak large-scale poloidal magnetic field, and the central star has no strong stellar magnetosphere initially. Our simulation investigates the structure of the accretion flows from a turbulent accretion disk onto the star. The simulation reveals that fast accretion onto the star at high latitudes occurs even without a stellar magnetosphere. We find that the failed disk wind becomes the fast, high-latitude accretion as a result of angular momentum exchange like the magneto-rotational instability (MRI) well above the disk, where the Lorentz force that decelerates the rotational motion of gas can be comparable to the centrifugal force. Unlike the classical magnetospheric accretion scenario, fast accretion streams are not guided by magnetic fields of the stellar magnetosphere. Nevertheless, the accretion velocity reaches the free-fall velocity at the stellar surface due to the efficient angular momentum loss at a distant place from the star. This study provides a possible explanation why Herbig Ae/Be stars whose magnetic fields are generally not strong enough to form magnetospheres also show indications of fast accretion. A magnetically-driven jet is not formed from the disk in our model. The differential rotation cannot generate sufficiently strong magnetic fields for the jet acceleration, because the Parker instability interrupts the field amplification.

  • Note on fast spinning neutron stars with unified equations of states.- [PDF] - [Article] - [UPDATED]

    A. Li, N. B. Zhang, B. Qi, G. F. Burgio

    For the propose of confronting updated pulsar observations with developed neutron star equation of states (EoSs), we employ four unified EoSs for both the core and the crust, namely BCPM, BSk20, BSk21, Shen-TM1, as well as two non-unified EoSs widely used in the literature, i.e. APR and GM1 EoS, which are commonly matched with the Negele-Vautherin and the Baym-Pethick-Sutherland crust EoS. All the core EoSs satisfy the recent observational constraints of the two massive pulsars whose masses are precisely measured. We show that the NS mass-equatorial radius relations are slightly affected by the smoothness at the core-crust matching interface. Moreover, the uncertainties in the crust EoS and the matching interface bring insignificant changes, even at maximally rotating (Keplerian) configurations. We also find that for all four unified EoSs, rotation can increase the star's gravitational mass up to $18\%-19\%$ and the equatorial radius by $29\%-36\%$, which are consistent with the previous calculations using non-unified EoSs. For stars as heavy as 1.4 M$_{\odot}$, the radius increase is more pronounced, reaching $41\%-43\%$, i.e. $5-6$ km. Moreover, by confronting the results using unified EoSs, which give the correct empirical values at saturation density, with two controversial determinations of the radius for the fast rotator 4U 1608-52, we address that a small radius may be better justified for this source.

  • Optical Precursors to Black Hole X-ray Binary Outbursts: An evolving synchrotron jet spectrum in Swift J1357.2-0933.- [PDF] - [Article] - [UPDATED]

    David M. Russell, Ahlam Al Qasim, Federico Bernardini, Richard M. Plotkin, Fraser Lewis, 4), Karri I. I. Koljonen, 6), Yi-Jung Yang, (2) International Centre for Radio Astronomy Research - Curtin University, (3) Faulkes Telescope Project, School of Physics, and Astronomy, Cardiff University, (4) Astrophysics Research Institute, Liverpool John Moores University, (5) Finnish Centre for Astronomy with ESO (FINCA), University of Turku, (6) Aalto University Metsahovi Radio Observatory, (7) School of Physics and Astronomy, Sun Yat-Sen University)

    We present six years of optical monitoring of the black hole candidate X-ray binary Swift J1357.2-0933, during and since its discovery outburst in 2011. On these long timescales, the quiescent light curve is dominated by high amplitude, short term (seconds-days) variability spanning ~ 2 magnitudes, with an increasing trend of the mean flux from 2012 to 2017 that is steeper than in any other X-ray binary found to date (0.17 mag/yr). We detected the initial optical rise of the 2017 outburst of Swift J1357.2-0933, and we report that the outburst began between April 1 and 6, 2017. Such a steep optical flux rise preceding an outburst is expected according to disk instability models, but the high amplitude variability in quiescence is not. Previous studies have shown that the quiescent spectral, polarimetric and rapid variability properties of Swift J1357.2-0933 are consistent with synchrotron emission from a weak compact jet. We find that a variable optical/infrared spectrum is responsible for the brightening: a steep, red spectrum before and soon after the 2011 outburst evolves to a brighter, flatter spectrum since 2013. The evolving spectrum appears to be due to the jet spectral break shifting from the infrared in 2012 to the optical in 2013, then back to the infrared by 2016-2017 while the optical remains relatively bright. Swift J1357.2-0933 is a valuable source to study black hole jet physics at very low accretion rates, and is possibly the only quiescent source in which the optical jet properties can be regularly monitored.

  • On white holes as particle accelerators.- [PDF] - [Article] - [UPDATED]

    O. B. Zaslavskii

    We analyze scenarios of particle collisions in the metric of a nonextremal black hole that can potentially lead to ultrahigh energy $E_{c.m.}$ in their centre of mass frame. Particle 1 comes from infinity to the black hole horizon while particle 2 emerges from a white hole region. It is shown that unbounded $E_{c.m.}$ $\ $require that particle 2 pass close to the bifurcation point. The analogy with collisions inside the horizon is discussed.

  • Disrupted Globular Clusters and the Gamma-Ray Excess in the Galactic Centre.- [PDF] - [Article] - [UPDATED]

    Giacomo Fragione, Fabio Antonini, Oleg Y. Gnedin

    The Fermi Large Area Telescope has provided the most detailed view toward the Galactic Centre (GC) in high-energy gamma rays. Besides the interstellar emission and point-source contributions, the data suggest a residual diffuse gamma-ray excess. The similarity of its spatial distribution with the expected profile of dark matter has led to claims that this may be evidence for dark matter particle annihilation. Here, we investigate an alternative explanation that the signal originates from millisecond pulsars (MSPs) formed in dense globular clusters and deposited at the GC as a consequence of cluster inspiral and tidal disruption. We use a semi-analytical model to calculate the formation, migration, and disruption of globular clusters in the Galaxy. Our model reproduces the mass of the nuclear star cluster and the present-day radial and mass distribution of globular clusters. For the first time, we calculate the evolution of MSPs from disrupted globular clusters throughout the age of the Galaxy and consistently include the effect of the MSP spin-down due to magnetic-dipole breaking. The final gamma-ray amplitude and spatial distribution are in good agreement with the Fermi observations and provide a natural astrophysical explanation for the GC excess.

  • Science with the Cherenkov Telescope Array.- [PDF] - [Article] - [UPDATED]

    B.S. Acharya, I. Agudo, I. Al Samarai, R. Alfaro, J. Alfaro, C. Alispach, R. Alves Batista, J.-P. Amans, E. Amato, G. Ambrosi, E. Antolini, L.A. Antonelli, C. Aramo, M. Araya, T. Armstrong, F. Arqueros, L. Arrabito, K. Asano, M. Ashley, M. Backes, C. Balazs, M. Balbo, O. Ballester, J. Ballet, A. Bamba, M. Barkov, U. Barres de Almeida, J.A. Barrio, D. Bastieri, Y. Becherini, A. Belfiore, W. Benbow, D. Berge, E. Bernardini, M.G. Bernardini, M. Bernardos, K. Bernlöhr, B. Bertucci, B. Biasuzzi, C. Bigongiari, A. Biland, E. Bissaldi, J. Biteau, O. Blanch, J. Blazek, C. Boisson, J. Bolmont, G. Bonanno, A. Bonardi, C. Bonavolontà, G. Bonnoli, Z. Bosnjak, M. Böttcher, C. Braiding, J. Bregeon, A. Brill, A.M. Brown, P. Brun, G. Brunetti, T. Buanes, et al. (521 additional authors not shown)

    The Cherenkov Telescope Array, CTA, will be the major global observatory for very high energy gamma-ray astronomy over the next decade and beyond. The scientific potential of CTA is extremely broad: from understanding the role of relativistic cosmic particles to the search for dark matter. CTA is an explorer of the extreme universe, probing environments from the immediate neighbourhood of black holes to cosmic voids on the largest scales. Covering a huge range in photon energy from 20 GeV to 300 TeV, CTA will improve on all aspects of performance with respect to current instruments. The observatory will operate arrays on sites in both hemispheres to provide full sky coverage and will hence maximize the potential for the rarest phenomena such as very nearby supernovae, gamma-ray bursts or gravitational wave transients. With 99 telescopes on the southern site and 19 telescopes on the northern site, flexible operation will be possible, with sub-arrays available for specific tasks. CTA will have important synergies with many of the new generation of major astronomical and astroparticle observatories. Multi-wavelength and multi-messenger approaches combining CTA data with those from other instruments will lead to a deeper understanding of the broad-band non-thermal properties of target sources. The CTA Observatory will be operated as an open, proposal-driven observatory, with all data available on a public archive after a pre-defined proprietary period. Scientists from institutions worldwide have combined together to form the CTA Consortium. This Consortium has prepared a proposal for a Core Programme of highly motivated observations. The programme, encompassing approximately 40% of the available observing time over the first ten years of CTA operation, is made up of individual Key Science Projects (KSPs), which are presented in this document.

  • Neutrino transport in black hole-neutron star binaries: neutrino emission and dynamical mass ejection.- [PDF] - [Article] - [UPDATED]

    Koutarou Kyutoku, Kenta Kiuchi, Yuichiro Sekiguchi, Masaru Shibata, Keisuke Taniguchi

    We study the merger of black hole-neutron star binaries by fully general-relativistic neutrino-radiation-hydrodynamics simulations throughout the coalescence, particularly focusing on the role of neutrino irradiation in dynamical mass ejection. Neutrino transport is incorporated by an approximate transfer scheme based on the truncated moment formalism. While we fix the mass ratio of the black hole to the neutron star to be 4 and the dimensionless spin parameter of the black hole to be 0.75, the equations of state for finite-temperature neutron-star matter are varied. The hot accretion disk formed after tidal disruption of the neutron star emits a copious amount of neutrinos with the peak total luminosity ~1--3x10^53 erg s^(-1) via thermal pair production and subsequent electron/positron captures on free nucleons. Nevertheless, the neutrino irradiation does not modify significantly the electron fraction of the dynamical ejecta from the neutrinoless beta-equilibrium value at zero temperature of initial neutron stars. The mass of the wind component driven by neutrinos from the remnant disk is negligible compared to the very neutron-rich dynamical component, throughout our simulations performed until a few tens milliseconds after the onset of merger, for the models considered in this study. These facts suggest that the ejecta from black hole-neutron star binaries are very neutron rich and are expected to accommodate strong r-process nucleosynthesis, unless magnetic or viscous processes contribute substantially to the mass ejection from the disk. We also find that the peak neutrino luminosity does not necessarily increase as the disk mass increases, because tidal disruption of a compact neutron star can result in a remnant disk with a small mass but high temperature.

  • GRB170817A associated with GW170817: multifrequency observations and modeling of prompt gamma-ray emission.- [PDF] - [Article] - [UPDATED]

    Alexei Pozanenko, Maxim V. Barkov, Pavel Yu. Minaev, Alina A. Volnova, Elena D. Mazaeva, Alexander S. Moskvitin, Maxim A. Krugov, Vladimir A. Samodurov, Vladimir M. Loznikov, Maxim Lyutikov

    We present our observations of electromagnetic transients associated with GW170817/GRB 170817A using optical telescopes of Chilescope observatory and Big Scanning Antenna (BSA) of Pushchino Radio Astronomy Observatory at 110MHz. The Chilescope observatory detected an optical transient of $\sim19^m$ on the third day in the outskirts of the galaxy NGC 4993; we continued observations following its rapid decrease. We put an upper limit of $1.5\times10^{4}$ Jy on any radio source with a duration of 10-60 s which may be associated with GW170817/GRB 170817A. The prompt gamma-ray emission consists of two distinctive components - a hard short pulse delayed by $\sim2$ seconds with respect to the LIGO signal and softer thermal pulse with $T\sim 10 $ keV lasting for another $\sim2$ seconds. The appearance of a thermal component at the end of the burst is unusual for short GRBs. Both the hard and the soft components do not satisfy the Amati relation, making GRB 170817A distinctively different from other short GRBs. Based on gamma-ray and optical observations, we develop a model for the prompt high-energy emission associated with GRB 170817A. The merger of two neutron stars creates an accretion torus of $\sim10^{-2} M_\odot$, which supplies the black hole with magnetic flux and confines the Blandford-Znajek-powered jet. We associate the hard prompt spike with the quasispherical breakout of the jet from the disk wind. As the jet plows through the wind with subrelativistic velocity, it creates a radiation-dominated shock that heats the wind material to tens of kiloelectron volts, producing the soft thermal component.

  • A Census of Southern Pulsars at 185 MHz.- [PDF] - [Article] - [UPDATED]

    Mengyao Xue, N. D. R. Bhat, S. E. Tremblay, S. M. Ord, C. Sobey, N. A. Swainston, D. L. Kaplan, Simon Johnston, B. W. Meyers, S. J. McSweeney

    The Murchison Widefield Array (MWA), and its recently-developed Voltage Capture System (VCS), facilitates extending the low-frequency range of pulsar observations at high-time and -frequency resolution in the Southern Hemisphere, providing further information about pulsars and the ISM. We present the results of an initial time-resolved census of known pulsars using the MWA. To significantly reduce the processing load, we incoherently sum the detected powers from the 128 MWA tiles, which yields ~10% of the attainable sensitivity of the coherent sum. This preserves the large field-of-view (~450 deg2 at 185 MHz), allowing multiple pulsars to be observed simultaneously. We developed a WIde-field Pulsar Pipeline (WIPP) that processes the data from each observation and automatically folds every known pulsar located within the beam. We have detected 50 pulsars to date, 6 of which are millisecond pulsars. This is consistent with our expectation, given the telescope sensitivity and the sky coverage of the processed data (~17,000 deg2). For ten pulsars, we present the lowest-frequency detections published. For a subset of the pulsars, we present multi-frequency pulse profiles by combining our data with published profiles from other telescopes. Since the MWA is a low-frequency precursor to the Square Kilometre Array (SKA), we use our census results to forecast that a survey using Phase 1 of SKA-Low (SKA1-Low) can potentially detect around 9400 pulsars.

  • Astrophysical Black Holes: A Compact Pedagogical Review.- [PDF] - [Article] - [UPDATED]

    Cosimo Bambi

    Black holes are among the most extreme objects that can be found in the Universe and an ideal laboratory for testing fundamental physics. This article will briefly review the basic properties of black holes as expected from general relativity, the main astronomical observations, and the leading astrophysical techniques to probe the strong gravity region of these objects. It is mainly intended to provide a compact introductory overview on astrophysical black holes to new students entering this research field, as well as to senior researchers working in general relativity and alternative theories of gravity and wishing to quickly learn the state of the art of astronomical observations of black holes.

  • The evolution of GX 339-4 in the low-hard state as seen by NuSTAR and Swift.- [PDF] - [Article] - [UPDATED]

    Jingyi Wang-Ji, Javier A. García, James F. Steiner, John A. Tomsick, Fiona A. Harrison, Cosimo Bambi, Pierre-Olivier Petrucci, Jonathan Ferreira, Susmita Chakravorty, Maïca Clavel

    We analyze eleven NuSTAR and Swift observations of the black hole X-ray binary GX 339-4 in the hard state, six of which were taken during the end of the 2015 outburst, five during a failed outburst in 2013. These observations cover luminosities from 0.5%-5% of the Eddington luminosity. Implementing the most recent version of the reflection model relxillCp, we perform simultaneous spectral fits on both datasets to track the evolution of the properties in the accretion disk including the inner edge radius, the ionization, and temperature of the thermal emission. We also constrain the photon index and electron temperature of the primary source (the "corona"). We find the disk becomes more truncated when the luminosity decreases, and observe a maximum truncation radius of $37R_g$. We also explore a self-consistent model under the framework of coronal Comptonization, and find consistent results regarding the disk truncation in the 2015 data, providing a more physical preferred fit for the 2013 observations.

  • Scalar dark matter explanation of the DAMPE data in the minimal Left-Right symmetric model.- [PDF] - [Article] - [UPDATED]

    Junjie Cao, Xiaofei Guo, Liangliang Shang, Fei Wang, Peiwen Wu, Lei Zu

    Left-Right symmetric model (LRSM) has been an attractive extension of the Standard Model (SM) which can address the origin of parity violation in the SM electroweak (EW) interactions, generate tiny neutrino masses, accommodate dark matter (DM) candidates and provide a natural framework for baryogenesis through leptogenesis. In this work we utilize the minimal LRSM to study the recently reported DAMPE results of cosmic $e^+e^-$ spectrum which exhibits a tentative peak around 1.4 TeV, while satisfying the current neutrino data. We propose to explain the DAMPE peak with scalar DM $m_\chi\sim$ 3 TeV in two scenarios: 1) $\chi\chi \to H_1^{++}H_1^{--} \to \ell_i^+\ell_i^+\ell_j^-\ell_j^-$; 2) $\chi\chi \to H_{k}^{++}H_{k}^{--} \to \ell_i^+\ell_i^+\ell_j^-\ell_j^-$ accompanied by $\chi\chi \to H_1^+ H_1^- \to \ell_i^+ \nu_{\ell_i} \ell_j^- \nu_{\ell_j}$ with $\ell_{i,j}=e,\mu,\tau$ and $k=1,2$. We impose various experimental constraints such as accommodation of a SM-like Higgs, the observed DM relic abundance, DM direct detection bounds, lepton flavor violation measurements and EW precision observables. We also fit the theoretical prediction on $e^+e^-$ spectrum to relevant experimental data to determine the scalar mass spectrum favored by the DAMPE excess. We find that there are ample parameter space which can interpret the DAMPE data while passing the above constraints. Our explanations, on the other hand, usually imply the existence of other new physics at the energy scale ranging from $10^8 {\rm GeV}$ to $10^{12} {\rm GeV}$. Collider tests of our explanations are also discussed.

  • Indications of an unexpected signal associated with the GW170817 binary neutron star inspiral.- [PDF] - [Article] - [UPDATED]

    E. Fischbach, V. E. Barnes, N. Cinko, J. Heim, H. B. Kaplan, D. E. Krause, J. R. Leeman, S. A. Mathews, M. J. Mueterthies, D. Neff, M. Pattermann

    We report experimental evidence at the 2.5$\sigma$ level for an unexpected signal associated with the GW170817 binary neutron star inspiral. This evidence derives from a laboratory experiment simultaneously measuring the $\beta$-decay rates of Si-32 and Cl-36 in a common detector. Whereas the Si-32 and Cl-36 decay rates show no statistical correlation before or after the inspiral, they are highly correlated ($\sim 95\%$) in the 5 hour time interval immediately following the inspiral. If we interpret this correlation as arising from the influence of particles emitted during the inspiral, then we can estimate the mass $m_{x}$ of these particles from the time delay between the gravity-wave signal and a peak in the $\beta$-decay data. We find for particles of energy 10 MeV, $m_{x}$ $\lesssim$ 16 eV which includes the neutrino mass region $m_{\nu}$ $\lesssim$ 2 eV. The latter is based on existing limits for the masses $m_{i}$ of the three known neutrino flavors. Additionally, we find that the correlation is even stronger if we include data in the 80 minute period before the arrival of the gravity wave signal. Given the large number of radionuclides whose decays are being monitored at any given time, we conjecture that other groups may also be in a position to search for statistically suggestive fluctuations of radionuclide decay rates associated with the GW170817 inspiral.

  • Accretion of clumpy cold gas onto massive black hole binaries: a possible fast route to binary coalescence.- [PDF] - [Article] - [UPDATED]

    Felipe G. Goicovic, Cristian Maureira-Fredes, Alberto Sesana, Pau Amaro-Seoane, Jorge Cuadra

    In currently favoured hierarchical cosmologies, the formation of massive black hole binaries (MBHBs) following galaxy mergers is unavoidable. Still, due the complex physics governing the (hydro)dynamics of the post-merger dense environment of stars and gas in galactic nuclei, the final fate of those MBHBs is still unclear. In gas-rich environments, it is plausible that turbulence and gravitational instabilities feed gas to the nucleus in the form of a series of cold incoherent clumps, thus providing a way to exchange energy and angular momentum between the MBHB and its surroundings. Within this context, we present a suite of smoothed-particle-hydrodynamical models to study the evolution of a sequence of near-radial turbulent gas clouds as they infall towards equal-mass, circular MBHBs. We focus on the dynamical response of the binary orbit to different levels of anisotropy of the incoherent accretion events. Compared to a model extrapolated from a set of individual cloud-MBHB interactions, we find that accretion increases considerably and the binary evolution is faster. This occurs because the continuous infall of clouds drags inwards circumbinary gas left behind by previous accretion events, thus promoting a more effective exchange of angular momentum between the MBHB and the gas. These results suggest that sub-parsec MBHBs efficiently evolve towards coalescence during the interaction with a sequence of individual gas pockets.

  • A New Type of Extreme-mass-ratio Inspirals Produced by Tidal Capture of Binary Black Holes.- [PDF] - [Article] - [UPDATED]

    Xian Chen, Wen-Biao Han, (2) SHAO)

    Extreme-mass-ratio inspiral (EMRI) is an important gravitational-wave (GW) source and it normally consists of one stellar-mass black hole (BH) whirling closely around a supermassive black hole (SMBH). In this Letter, we demonstrate that the small body, in fact, could be a BH binary (BHB). Previous numerical scatting experiments have shown that SMBHs can tidally capture BHBs to bound orbits. Here we investigate the subsequent long-term evolution. We find that those BHBs with a semi-major axis of $a\lesssim5\times10^{-3}$ AU can be captured to tightly-bound orbits such that they will successfully inspiral towards the central SMBHs without being scattered away by stellar relaxation processes. We estimate that these binary-EMRIs (b-EMRIs) could constitute at most $10\%$ percent of the EMRI population. Moreover, we show that when the eccentricity of a b-EMRI drops to about $0.85$, the two stellar BHs will quickly merge due to the tidal perturbation by the SMBH. The high-frequency ($\sim10^2$ Hz) GWs generated during the coalescence coincide with the low-frequency ($\sim10^{-3}$ Hz) waves from the b-EMRI, making this system an ideal target for future multi-band GW observations.


  • Galactic disk winds driven by cosmic ray pressure.- [PDF] - [Article]

    S. Alwin Mao, Eve C. Ostriker

    Cosmic ray pressure gradients transfer energy and momentum to extraplanar gas in disk galaxies, potentially driving significant mass loss as galactic winds. This may be particularly important for launching high-velocity outflows of "cool" (T < 10^4 K) gas. We study cosmic-ray driven disk winds using a simplified semi-analytic model assuming streamlines follow the large-scale gravitational potential gradient. We consider scaled Milky Way-like potentials including a disk, bulge, and halo with a range of halo velocities V_H = 50-300 km/s, and streamline footpoints with radii in the disk R_0=1-16 kpc at height 1 kpc. Our solutions cover a wide range of footpoint gas velocity u_0, magnetic-to-cosmic-ray pressure ratio, gas-to-cosmic-ray pressure ratio, and angular momentum. Cosmic ray streaming at the Alfv\'en speed enables the effective sound speed C_eff to increase from the footpoint to a critical point where C_eff,c = u_c ~ V_H; this differs from thermal winds in which C_eff decreases outward. The critical point is typically at a height of 1-6 kpc from the disk, increasing with V_H, and the asymptotic wind velocity exceeds the escape speed of the halo. Mass loss rates are insensitive to the footpoint values of the magnetic field and angular momentum. In addition to numerical parameter space exploration, we develop and compare to analytic scaling relations. We show that winds have mass loss rates per unit area up to ~ Pi_0 V_H^-5/3 u_0^2/3 where Pi_0 is the footpoint cosmic ray pressure and u_0 is set by the upwelling of galactic fountains. The predicted wind mass-loss rate exceeds the star formation rate for V_H < 200 km/s and u_0 = 50 km/s, a typical fountain velocity.

  • Kinematics of the SN Refsdal host revealed by MUSE: a regularly rotating spiral galaxy at z~1.5.- [PDF] - [Article]

    E. M. Di Teodoro, C. Grillo, F. Fraternali, R. Gobat, W. Karman, A. Mercurio, P. Rosati, I. Balestra, G. B. Caminha, K. I. Caputi, M. Lombardi, S. H. Suyu, T. Treu, E. Vanzella

    We use Multi Unit Spectroscopic Explorer (MUSE) observations of the galaxy cluster MACS J1149.5+2223 to explore the kinematics of the grand-design spiral galaxy Sp1149 hosting the SN Refsdal. Sp1149 lies at $z\simeq1.49$, has a stellar mass $M_*\simeq5\times10^9 \, \mathrm{M_\odot}$, a star-formation rate $\mathrm{SFR} \simeq1-6 \, \mathrm{M_\odot/yr}$ and represents a likely progenitor of a Milky-Way-like galaxy. All the four multiple images of Sp1149 in our data show strong OII-line emissions pointing to a clear rotation pattern. We take advantage of the gravitational lensing magnification effect ($\simeq 4 \times$) on the OII emission of the least distorted image to fit 3D kinematic models to the MUSE data-cube and derive the rotation curve and the velocity dispersion profile of Sp1149. We find that the rotation curve steeply rises, peaks at $R\simeq1$ kpc and then (initially) declines and flattens to an average $V_\mathrm{flat} = 128^{+29}_{-19}$ km/s. The shape of the rotation curve is well determined but the actual value of $V_\mathrm{flat}$ is quite uncertain because of the nearly face-on configuration of the galaxy. The intrinsic velocity dispersion due to gas turbulence is almost constant across the entire disc with an average of $27\pm5$ km/s. This value is consistent with $z=0$ measurements in the ionized gas component and a factor 2-4 lower than other estimates in different galaxies at similar redshifts. The average stellar-to-total mass fraction is of the order of one fifth. Our kinematic analysis returns the picture of a regular star-forming, mildly turbulent, rotation-dominated ($V / \sigma\simeq5$) spiral galaxy in a 4 Gyr old Universe.

  • ALMA Reveals an Inhomogeneous Compact Rotating Dense Molecular Torus at the NGC 1068 Nucleus.- [PDF] - [Article]

    Masatoshi Imanishi, Kouichiro Nakanishi, Takuma Izumi, Keiichi Wada, (2) Kagoshima University)

    We present the results of our ALMA Cycle 4 high-spatial-resolution (0.04-0.07") observations, at HCN J=3-2 and HCO+ J=3-2 lines, of the nucleus of NGC 1068, the nearby prototypical type 2 active galactic nucleus (AGN). Our previous ALMA observations identified the compact emission of these lines at the putative location of the torus around a mass-accreting supermassive black hole. We now report that we have detected the rotation of this compact emission, with the eastern and western sides being redshifted and blueshifted, respectively. Unlike the previously reported CO J=6-5 emission, both the morphological and dynamical alignments of the HCN J=3-2 and HCO+ J=3-2 emission are roughly aligned along the east-west direction (i.e., the expected torus direction), suggesting that these molecular lines are better probes of a rotating dense molecular gas component in the torus. The western part of the torus exhibits larger velocity dispersion and stronger emission in the HCN J=3-2 and HCO+ J=3-2 lines than the eastern part, revealing a highly inhomogeneous molecular torus. The dense molecular gas in the torus and that of the host galaxy at 0.5-2.0" from the AGN along the torus direction are found to be counter-rotating, suggesting an external process happened in the past at the NGC 1068 nucleus.

  • The SAMI Galaxy Survey: gas content and interaction as the drivers of kinematic asymmetry.- [PDF] - [Article]

    J.V.Bloom, S.M.Croom, J.J.Bryant, A.L.Schaefer, J.Bland-Hawthorn, S.Brough, J.Callingham, L.Cortese, C.Federrath, N.Scott, J.vandeSande, F.D'Eugenio, S.Sweet, C.Tonini, J.T.Allen, M.Goodwin, A.W.Green, I.S.Konstantopoulos, J.Lawrence, N.Lorente, A.M.Medling, M.S.Owers, S.N.Richards, R.Sharp

    In order to determine the causes of kinematic asymmetry in the H$\alpha$ gas in the SAMI Galaxy Survey sample, we investigate the comparative influences of environment and intrinsic properties of galaxies on perturbation. We use spatially resolved H$\alpha$ velocity fields from the SAMI Galaxy Survey to quantify kinematic asymmetry ($\overline{v_{asym}}$) in nearby galaxies and environmental and stellar mass data from the GAMA survey. {We find that local environment, measured as distance to nearest neighbour, is inversely correlated with kinematic asymmetry for galaxies with $\mathrm{\log(M_*/M_\odot)}>10.0$, but there is no significant correlation for galaxies with $\mathrm{\log(M_*/M_\odot)}<10.0$. Moreover, low mass galaxies ($\mathrm{\log(M_*/M_\odot)}<9.0$) have greater kinematic asymmetry at all separations, suggesting a different physical source of asymmetry is important in low mass galaxies.} We propose that secular effects derived from gas fraction and gas mass may be the primary causes of asymmetry in low mass galaxies. High gas fraction is linked to high $\frac{\sigma_{m}}{V}$ (where $\sigma_m$ is H$\alpha$ velocity dispersion and $V$ the rotation velocity), which is strongly correlated with $\overline{v_{asym}}$, and galaxies with $\log(M_*/M_\odot)<9.0$ have offset $\overline{\frac{\sigma_{m}}{V}}$ from the rest of the sample. Further, asymmetry as a fraction of dispersion decreases for galaxies with $\log(M_*/M_\odot)<9.0$. Gas mass and asymmetry are also inversely correlated in our sample. We propose that low gas masses in dwarf galaxies may lead to asymmetric distribution of gas clouds, leading to increased relative turbulence.

  • Class I methanol masers in low-mass star formation regions.- [PDF] - [Article]

    S. Kalenskii, S. Kurtz, P. Hofner, P. Bergman, C.M. Walmsley, P. Golysheva

    We present a review of the properties of Class I methanol masers detected in low-mass star forming regions (LMSFRs). These masers, henceforth called LMMIs, are associated with postshock gas in the lobes of chemically active outflows in LMSFRs NGC1333, NGC2023, HH25, and L1157. LMMIs share the main properties with powerful masers in regions of massive star formation and are a low-luminosity edge of the total Class I maser population. However, the exploration of just these objects may push forward the exploration of Class I masers, since many LMSFRs are located only 200--300 pc from the Sun, making it possible to study associated objects in detail. EVLA observations with a $0.2"$ spatial resolution show that the maser images consist of unresolved or barely resolved spots with brightness temperatures up to $5\times 10^5$ K. The results are "marginally" consistent with the turbulent model of maser emission.

  • A Dust spectral energy distribution model with hierarchical Bayesian inference. I. Formalism & benchmarking.- [PDF] - [Article]

    F. Galliano

    This article presents a new dust SED model, named HerBIE, aimed at eliminating the noise-induced correlations and large scatter obtained when performing least-squares fits. The originality of this code is to apply the hierarchical Bayesian approach to full dust models, including realistic optical properties, stochastic heating and the mixing of physical conditions in the observed regions. We test the performances of our model by applying it to synthetic observations. We explore the impact on the recovered parameters of several effects: signal-to-noise ratio, SED shape, sample size, the presence of intrinsic correlations, the wavelength coverage and the use of different SED model components. We show that this method is very efficient: the recovered parameters are consistently distributed around their true values. We do not find any clear bias, even for the most degenerate parameters, or with extreme signal-to-noise ratios.

  • Deuterated Formaldehyde in the low mass protostar HH212.- [PDF] - [Article]

    Dipen Sahu, Young-Chol Minh, Chin-Fei Lee, Sheng-Yuan Liu, Ankan Das, Sandip K. Chakrabarti, Bhala Sivaraman

    HH212, a nearby (400 pc) object in Orion, is a Class 0 protostellar system with a Keplerian disk and collimated bipolar SiO jets. Deuterated water, HDO and a deuterated complex molecule, methanol (CH2DOH) have been reported in the source. Here, we report the HDCO (deuterated formaldehyde) line observation from ALMA data to probe the inner region of HH212. We compare HDCO line with other molecular lines to understand the possible chemistry and physics of the source. The distribution of HDCO emission suggests it may be associated with the base of the outflow. The emission also shows a rotation but it is not associated with the Keplerian rotation of disk or the rotating infalling envelope, rather it is associated with the outflow as previously seen in C 34 S. From the possible deuterium fractionation, we speculate that the gas phase formation of deuterated formaldehyde is active in the central hot region of the low-mass protostar system, HH212.

  • Knotty protostellar jets as a signature of episodic protostellar accretion?.- [PDF] - [Article]

    Eduard Vorobyov, 2, 3), Vardan Elbakyan, Adele Plunkett, Michael Dunham, Marc Audard, Manuel Guedel, Odysseas Dionatos, TU Wien, Vienna, 1060, Austria, (2) Research Institute of Physics, Southern Federal University, Roston-on-Don, 344090 Russia, (3) University of Vienna, Department of Astrophysics, Vienna, 1180, Austria, (4) European Southern Observatory, Av. Alonso de Cordova 3107, Vitacura, Santiago de Chile, Chile, (5) Department of Physics, State University of New York at Fredonia, 280 Central Ave, Fredonia, NY 14063, (6) Department of Astronomy, University of Geneva, 1290 Versoix, Switzerland)

    We aim at studying the causal link between the knotty jet structure in CARMA 7, a young Class 0 protostar in the Serpens South cluster, and episodic accretion in young protostellar disks. We used numerical hydrodynamics simulations to derive the protostellar accretion history in gravitationally unstable disks around solar-mass protostars. We compared the time spacing between luminosity bursts \Delta\tau_mod, caused by dense clumps spiralling on the protostar, with the differences of dynamical timescales between the knots \Delta\tau_obs in CARMA 7. We found that the time spacing between the bursts have a bi-modal distribution caused by isolated and clustered luminosity bursts. The former are characterized by long quiescent periods between the bursts with \Delta\tau_mod = a few * (10^3-10^4) yr, whereas the latter occur in small groups with time spacing between the bursts \Delta\tau_mod= a few * (10-10^2) yr. For the clustered bursts, the distribution of \Delta\tau_mod in our models can be fit reasonably well to the distribution of \Delta\tau_obs in the protostellar jet of CARMA 7, if a certain correction for the (yet unknown) inclination angle with respect to the line of sight is applied. The K-S test on the model and observational data sets suggests the best-fit values for the inclination angles of 55-80 deg., which become narrower (75-80 deg.) if only strong luminosity bursts are considered. The dynamical timescales of the knots in the jet of CARMA 7 are too short for a meaningful comparison with the long time spacings between isolated bursts in our models. The exact sequences of time spacings between the luminosity bursts in our models and knots in the jet of CARMA 7 were found difficult to match. (abridged)

  • A multiwavelength survey of HI-excess galaxies with surprisingly inefficient star formation.- [PDF] - [Article]

    K. Gereb, S. Janowiecki, B. Catinella, L. Cortese, V. Kilborn

    We present the results of a multiwavelength survey of HI-excess galaxies, an intriguing population with large HI reservoirs associated with little current star formation. These galaxies have stellar masses $M_{\star} >10^{10}$ M$_{\odot}$, and were identified as outliers in the gas fraction vs. NUV$-r$ color and stellar mass surface density scaling relations based on the GALEX Arecibo SDSS Survey (GASS). We obtained HI interferometry with the GMRT, Keck optical long-slit spectroscopy and deep optical imaging (where available) for four galaxies. Our analysis reveals multiple possible reasons for the HI excess in these systems. One galaxy, AGC 10111, shows an HI disk that is counter-rotating with respect to the stellar bulge, a clear indication of external origin of the gas. Another galaxy appears to host a Malin 1-type disk, where a large specific angular momentum has to be invoked to explain the extreme $M_{\rm HI}$/$M_{\star}$ ratio of 166$\%$. The other two galaxies have early-type morphology with very high gas fractions. The lack of merger signatures (unsettled gas, stellar shells and streams) in these systems suggests that these gas-rich disks have been built several Gyr-s ago, but it remains unclear how the gas reservoirs were assembled. Numerical simulations of large cosmological volumes are needed to gain insight into the formation of these rare and interesting systems.

  • The early evolution of viscous and self-gravitating circumstellar disks with a dust component.- [PDF] - [Article]

    Eduard Vorobyov, 2, 3), Vitaly Akimkin, Olga Stoyanovskaya, Yaroslav Pavlyuchenkov, Hauyu Baobab Liu, TU Wien, 1060, Vienna, Austria, (2) Research Institute of Physics, Southern Federal University, Stachki Ave. 194, 344090, Rostov-on-Don, Russia, (3) Department of Astrophysics, University of Vienna, Vienna, 1180, Austria, (4) Institute of Astronomy, Russian Academy of Sciences, Pyatnitskaya str. 48, 119017, Moscow, Russia, (5) Novosibirsk State University, Lavrentieva str. 2, 630090, Novosibirsk, Russia and Boreskov Institute of Catalysis, Lavrentieva str. 5, 630090, Novosibirsk, Russia, (6) European Southern Observatory (ESO), Karl-Schwarzschild-Str. 2, D-85748 Garching, Germany)

    The long-term evolution of a circumstellar disk starting from its formation and ending in the T Tauri phase was simulated numerically with the purpose of studying the evolution of dust in the disk with distinct values of viscous \alpha-parameter and dust fragmentation velocity v_frag. We solved numerical hydrodynamics equations in the thin-disk limit, which are modified to include a dust component consisting of two parts: sub-micron-sized dust and grown dust with a maximum radius a_r. The former is strictly coupled to the gas, while the latter interacts with the gas via friction. The conversion of small to grown dust, dust growth, and dust self-gravity are also considered. We found that the process of dust growth known for the older protoplanetary phase also holds for the embedded phase of disk evolution. The dust growth efficiency depends on the radial distance from the star - a_r is largest in the inner disk and gradually declines with radial distance. In the inner disk, a_r is limited by the dust fragmentation barrier. The process of small-to-grown dust conversion is very fast once the disk is formed. The total mass of grown dust in the disk (beyond 1 AU) reaches tens or even hundreds of Earth masses already in the embedded phase of star formation and even a greater amount of grown dust drifts in the inner, unresolved 1 AU of the disk. Dust does not usually grow to radii greater than a few cm. A notable exception are models with \alpha <= 10^{-3}, in which case a zone with reduced mass transport develops in the inner disk and dust can grow to meter-sized boulders in the inner 10 AU. Grown dust drifts inward and accumulates in the inner disk regions. This effect is most pronounced in the \alpha <= 10^{-3} models where several hundreds of Earth masses can be accumulated in a narrow region of several AU from the star by the end of embedded phase. (abridged).

  • Binary energy source of the HH 250 outflow and its circumstellar environment.- [PDF] - [Article]

    Fernando Comerón, Bo Reipurth, Hsi-Wei Yen, Michael S. Connelley

    Herbig-Haro flows are signposts of recent major accretion and outflow episodes. We aim to determine the nature and properties of the little-known outflow source HH 250-IRS, which is embedded in the Aquila clouds. We have obtained adaptive optics-assisted L-band images with the NACO instrument on the Very Large Telescope (VLT), together with N- and Q-band imaging with VISIR also on the VLT. Using the SINFONI instrument on the VLT we carried out H- and K-band integral field spectroscopy of HH 250-IRS, complemented with spectra obtained with the SpeX instrument at the InfraRed Telescope Facility (IRTF) in the JHKL bands. Finally, the SubMillimeter Array (SMA) interferometer was used to study the circumstellar environment of HH 250-IRS at 225 and 351 GHz with CO (2-1) and CO (3-2) maps and 0.9 mm and 1.3 mm continuum images. The HH 250-IRS source is resolved into a binary with 0''53 separation, corresponding to 120 AU at the adopted distance of 225 pc. The individual components show heavily veiled spectra with weak CO absorption indicative of late-type stars. Both are Class I sources, but their spectral energy distributions between 1.5 $\mu$m and 19 $\mu$m differ markedly and suggest the existence of a large cavity around one of the components. The millimeter interferometric observations indicate that the gas mainly traces a circumbinary envelope or disk, while the dust emission is dominated by one of the circumstellar envelopes. HH 250-IRS is a new addition to the handful of multiple systems where the individual stellar components, the circumstellar disks and a circumbinary disk can be studied in detail, and a rare case among those systems in which a Herbig-Haro flow is present.

  • The LiteBIRD Satellite Mission - Sub-Kelvin Instrument.- [PDF] - [Article]

    A. Suzuki, P. A.R. Ade, Y. Akiba, D. Alonso, K. Arnold, J. Aumont, C. Baccigalupi, D. Barron, S. Basak, S. Beckman, J. Borrill, F. Boulanger, M. Bucher, E. Calabrese, Y. Chinone, S. Cho, B. Crill, A. Cukierman, D. W. Curtis, T. de Haan, M. Dobbs, A. Dominjon, T. Dotani, L. Duband, A. Ducout, J. Dunkley, J. M. Duval, T. Elleflot, H. K. Eriksen, J. Errard, J. Fischer, T. Fujino, T. Funaki, U. Fuskeland, K. Ganga, N. Goeckner-Wald, J. Grain, N. W. Halverson, T. Hamada, T. Hasebe, M. Hasegawa, K. Hattori, M. Hattori, L. Hayes, M. Hazumi, N. Hidehira, C. A. Hill, G. Hilton, J. Hubmayr, K. Ichiki, T. Iida, H. Imada, M. Inoue, Y. Inoue, K. D., H. Ishino, O. Jeong, H. Kanai, D. Kaneko, S. Kashima, N. Katayama, T. Kawasaki, S. A. Kernasovskiy, R. Keskitalo, A. Kibayashi, Y. Kida, K. Kimura, T. Kisner, et al. (85 additional authors not shown)

    Inflation is the leading theory of the first instant of the universe. Inflation, which postulates that the universe underwent a period of rapid expansion an instant after its birth, provides convincing explanation for cosmological observations. Recent advancements in detector technology have opened opportunities to explore primordial gravitational waves generated by the inflation through B-mode (divergent-free) polarization pattern embedded in the Cosmic Microwave Background anisotropies. If detected, these signals would provide strong evidence for inflation, point to the correct model for inflation, and open a window to physics at ultra-high energies. LiteBIRD is a satellite mission with a goal of detecting degree-and-larger-angular-scale B-mode polarization. LiteBIRD will observe at the second Lagrange point with a 400 mm diameter telescope and 2,622 detectors. It will survey the entire sky with 15 frequency bands from 40 to 400 GHz to measure and subtract foregrounds. The U.S. LiteBIRD team is proposing to deliver sub-Kelvin instruments that include detectors and readout electronics. A lenslet-coupled sinuous antenna array will cover low-frequency bands (40 GHz to 235 GHz) with four frequency arrangements of trichroic pixels. An orthomode-transducer-coupled corrugated horn array will cover high-frequency bands (280 GHz to 402 GHz) with three types of single frequency detectors. The detectors will be made with Transition Edge Sensor (TES) bolometers cooled to a 100 milli-Kelvin base temperature by an adiabatic demagnetization refrigerator.The TES bolometers will be read out using digital frequency multiplexing with Superconducting QUantum Interference Device (SQUID) amplifiers. Up to 78 bolometers will be multiplexed with a single SQUID amplidier. We report on the sub-Kelvin instrument design and ongoing developments for the LiteBIRD mission.

  • Magnetic Fields from Filaments to Cores.- [PDF] - [Article]

    Patrick M. Koch, Ya-Wen Tang, Nicholas L. Chapman, Ana Duarte-Cabral, Paul T.P. Ho, Giles Novak, Nicolas Peretto, Yu-Nung Su, Shigehisa Takakuwa, Hsi-Wei Yen

    How important is the magnetic (B-) field when compared to gravity and turbulence in the star-formation process? Does its importance depend on scale and location? We summarize submm dust polarization observations towards the large filamentary infrared dark cloud G34 and towards a dense core in the high-mass star-forming region W51. We detect B-field orientations that are either perpendicular or parallel to the G34 filament axis. These B-field orientations further correlate with local velocity gradients. Towards three cores in G34 we find a varying importance between B-field, gravity, and turbulence that seems to dictate varying types of fragmentation. At highest resolution towards the gravity-dominated collapsing core W51 e2 we resolve new B-field features, such as converging B-field lines and possibly magnetic channels.

  • Determination of the size of the dust torus in H0507+164 through optical and infrared monitoring.- [PDF] - [Article]

    Amit Kumar Mandal, Suvendu Rakshit, Kshama S. Kurian, C. S. Stalin, Blesson Mathew, Sebastian Hoenig, Poshak Gandhi, Ram Sagar, M. B. Pandge

    The time delay between flux variations in different wavelength bands can be used to probe the inner regions of active galactic nuclei (AGN). Here, we present the first measurements of the time delay between optical and near-infrared (NIR) flux variations in H0507+164, a nearby Seyfert 1.5 galaxy at z = 0.018. The observations in the optical V -band and NIR J, H and Ks bands carried over 35 epochs during the period October 2016 to April 2017 were used to estimate the inner radius of the dusty torus. From a careful reduction and analysis of the data using cross-correlation techniques, we found delayed responses of the J, H and Ks light curves to the V -band light curve. In the rest frame of the source, the lags between optical and NIR bands are found to be $27.1^{+13.5}_{-12.0}$ days (V vs. J), $30.4^{+13.9}_{-12.0}$ days (V vs. H) and $34.6^{+12.1}_{-9.6}$ days (V vs. K ). The lags between the optical and different NIR bands are thus consistent with each other. The measured lags indicate that the inner edge of dust torus is located at a distance of 0.029 pc from the central UV/optical AGN continuum. This is larger than the radius of the broad line region of this object determined from spectroscopic monitoring observations thereby supporting the unification model of AGN. The location of H0507+164 in the {\tau} - MV plane indicates that our results are in excellent agreement with the now known lag-luminosity scaling relationship for dust in AGN.

  • Emission-line diagnostics of nearby HII regions including interacting binary populations.- [PDF] - [Article]

    Lin Xiao, Elizabeth Stanway, J. J. Eldridge

    We present numerical models of the nebular emission from H II regions around young stellar populations over a range of compositions and ages. The synthetic stellar pop- ulations include both single stars and interacting binary stars. We compare these models to the observed emission lines of 254 HII regions of 13 nearby spiral galax- ies and 21 dwarf galaxies drawn from archival data. The models are created using the combination of the Binary Population and Spectral Synthesis (bpass) code with the photoionization code cloudy to study the differences caused by the inclusion of interacting binary stars in the stellar population. We obtain agreement with the observed emission line ratios from the nearby star-forming regions and discuss the effect of binary star evolution pathways on the nebular ionization of H II regions. We find that at population ages above 10 Myr, single-star models rapidly decrease in flux and ionization strength, while binary-star model still produce strong flux and high O III/H\b{eta} ratios. Our models can reproduce the metallicity of H II regions from spiral galaxies but we find higher metallicities than previously estimated for the H II regions from dwarf galaxies. Comparing the equivalent width of H\b{eta} emission between mod- els and observations, we find that accounting for ionizing photon leakage can affect age estimates for HII regions. When it is included, the typical age derived for HII regions is 5Myr from single-star models, and up to 10Myr with binary-star models. This is due to the existence of binary-star evolution pathways which produce more hot WR and helium stars at older ages. For future reference, we calculate new BPASS binary maximal starburst lines as a function of metallicity, and for the total model population, and present these in Appendix A.

  • Inner and outer star forming regions over the disks of spiral galaxies. I. Sample characterization.- [PDF] - [Article]

    M. Rodríguez-Baras, A. I. Díaz, F. F. Rosales-Ortega, S. F. Sánchez, (2) Instituto Nacional de Astrofísica, Óptica y Electrónica, (3) Universidad Nacional Autónoma de México)

    Context. The knowledge of abundance distributions is central to understanding the formation and evolution of galaxies. Most of the relations employed for the derivation of gas abundances have so far been derived from observations of outer disk HII regions, despite the known differences between inner and outer regions. Aims. Using integral field spectroscopy (IFS) observations we aim to perform a systematic study and comparison of two inner and outer HII regions samples. The spatial resolution of the IFS, the number of objects and the homogeneity and coherence of the observations allow a complete characterization of the main observational properties and differences of the regions. Methods. We analyzed a sample of 725 inner HII regions and a sample of 671 outer HII regions, all of them detected and extracted from the observations of a sample of 263 nearby, isolated, spiral galaxies observed by the CALIFA survey. Results. We find that inner HII regions show smaller equivalent widths, greater extinction and luminosities, along with greater values of [NII]{\lambda}6583/H{\alpha} and [OII]{\lambda}3727/[OIII]{\lambda}5007 emission-line ratios, indicating higher metallicites and lower ionization parameters. Inner regions have also redder colors and higher photometric and ionizing masses, although Mion/Mphot is slighty higher for the outer regions. Conclusions. This work shows important observational differences between inner and outer HII regions in star forming galaxies not previously studied in detail. These differences indicate that inner regions have more evolved stellar populations and are in a later evolution state with respect to outer regions, which goes in line with the inside-out galaxy formation paradigm.

  • H-band discovery of additional second-generation stars in the Galactic bulge globular cluster NGC 6522.- [PDF] - [Article]

    J. G. Fernández-Trincado, O. Zamora, Diogo Souto, R. E. Cohen, F. Dell'Agli, D. A. García-Hernández, T. Masseron, R. P. Schiavon, Sz. Mészáros, K. Cunha, Sten Hasselquist, M. Shetrone, J. Schiappacasse Ulloa, B. Tang, D. Geisler, D. R. G. Schleicher, S. Villanova, R. E. Mennickent, D. Minniti, J. Alonso-Garcia, A. Manchado, T. C. Beers, J. Sobeck, G. Zasowski, M. Schultheis, S. R. Majewski, A. Rojas-Arriagada, A. Almeida, F. Santana, R. J. Oelkers, P. Longa-Peña, R. Carrera, A. J. Burgasser, R. R. Lane, A. Roman-Lopes, Inese I. Ivans, F. R. Hearty

    We present elemental abundance analysis of high-resolution spectra for five giant stars, deriving Fe, Mg, Al, C, N, O, Si and Ce abundances, and spatially located within the innermost regions of the bulge globular cluster NGC 6522, based on H-band spectra taken with the multi-object APOGEEnorth spectrograph from the SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. Of the five cluster candidates, four stars are confirmed to have second-generation (SG) abundance patterns, with the basic pattern of depletion in C and Mg simultaneous with enrichment in N and Al as seen in other SG globular cluster populations at similar metallicity. In agreement with the most recent optical studies, the NGC 6522 stars analyzed exhibit (when available) only mild overabundances of the s-process element Ce, contradicting the idea of the NGC 6522 stars being formed from gas enriched by spinstars and indicating that other stellar sources such as massive AGB stars could be the primary intra-cluster medium polluters. The peculiar abundance signature of SG stars have been observed in our data, confirming the presence of multiple generations of stars in NGC 6522.

  • Accurate millimetre and submillimetre rest frequencies for $cis$- and $trans$-dithioformic acid, HCSSH.- [PDF] - [Article]

    D. Prudenzano, J. Laas, L. Bizzocchi, V. Lattanzi, C. Endres, B.M. Giuliano, S. Spezzano, M.E. Palumbo, P. Caselli

    A better understanding of sulphur chemistry is needed to solve the interstellar sulphur depletion problem. A way to achieve this goal is to study new S-bearing molecules in the laboratory, obtaining accurate rest frequencies for an astronomical search. We focus on dithioformic acid, HCSSH, which is the sulphur analogue of formic acid. The aim of this study is to provide an accurate line list of the two HCSSH $trans$ and $cis$ isomers in their electronic ground state and a comprehensive centrifugal distortion analysis with an extension of measurements in the millimetre and submillimetre range. We studied the two isomers in the laboratory using an absorption spectrometer employing the frequency-modulation technique. The molecules were produced directly within a free-space cell by glow discharge of a gas mixture. We measured lines belonging to the electronic ground state up to 478 GHz, with a total number of 204 and 139 new rotational transitions, respectively, for $trans$ and $cis$ isomers. The final dataset also includes lines in the centimetre range available from literature. The extension of the measurements in the mm and submm range lead to an accurate set of rotational and centrifugal distortion parameters. This allows us to predict frequencies with estimated uncertainties as low as 5 kHz at 1 mm wavelength. Hence, the new dataset provided by this study can be used for astronomical search.

  • Probing narrow-line Seyfert 1 galaxies in the southern hemisphere.- [PDF] - [Article]

    S. Chen, M. Berton, G. La Mura, E. Congiu, V. Cracco, L. Foschini, J.H. Fan, S. Ciroi, P. Rafanelli, D. Bastieri

    We present a new accurate catalog of narrow-line Seyfert 1 galaxies (NLS1s) in the southern hemisphere from the Six-degree Field Galaxy Survey (6dFGS) final data release, which is currently the most extensive spectroscopic survey available in the southern sky whose database has not yet been systematically explored. We classified 167 sources as NLS1s based on their optical spectral properties. We derived flux-calibrated spectra for the first time that the 6dFGS indeed does not provide. By analyzing these spectra, we obtained strong correlations between the monochromatic luminosity at 5100 A and the luminosity of Hbeta and [O III]5007 lines. The estimated central black hole mass and Eddington ratio have an average value of 9.55 x 10^6 M_Sun and 0.90 L_Edd respectively, which is a typical value for NLS1s. In the sample, 23 (13.8%) NLS1s were detected at radio frequencies, and 10 (6.0%) of them are radio-loud. Our results confirmed that radio-loud sources tend to have higher redshift, more massive black hole, and higher radio and optical luminosity than radio-quiet sources.

  • The innate origin of radial and vertical gradients in a simulated galaxy disc.- [PDF] - [Article] - [UPDATED]

    Julio F. Navarro, Cameron Yozin, Nic Loewen, Alejandro Benitez-Llambay, Azadeh Fattahi, Carlos S. Frenk, Kyle Oman, Joop Schaye, Tom Theuns

    We examine the origin of radial and vertical gradients in the age/metallicity of the stellar component of a galaxy disc formed in the APOSTLE cosmological hydrody- namical simulations. Some of these gradients resemble those in the Milky Way, where they have sometimes been interpreted as due to internal evolution, such as scattering off giant molecular clouds, radial migration driven by spiral patterns, or orbital reso- nances with a bar. Secular processes play a minor role in the simulated galaxy, which lacks strong spiral or bar patterns, and where such gradients arise as a result of the gradual enrichment of a gaseous disc that is born thick but thins as it turns into stars and settles into centrifugal equilibrium. The settling is controlled by the feedback of young stars; which links the star formation, enrichment, and equilibration timescales, inducing radial and vertical gradients in the gaseous disc and its descendent stars. The kinematics of coeval stars evolve little after birth and provide a faithful snapshot of the gaseous disc structure at the time of their formation. In this interpretation, the age-velocity dispersion relation would reflect the gradual thinning of the disc rather than the importance of secular orbit scattering; the outward flaring of stars would result from the gas disc flare rather than from radial migration; and vertical gradients would arise because the gas disc gradually thinned as it enriched. Such radial and vertical trends might just reflect the evolving properties of the parent gaseous disc, and are not necessarily the result of secular evolutionary processes.

  • Migration in the shearing sheet and estimates for young open cluster migration.- [PDF] - [Article] - [UPDATED]

    Alice C. Quillen, Eric Nolting, Ivan Minchev, Gayandhi De Silva, Cristina Chiappini

    Using tracer particles embedded in self-gravitating shearing sheet N-body simulations, we investigate the distance in guiding centre radius that stars or star clusters can migrate in a few orbital periods. The standard deviations of guiding centre distributions and maximum migration distances depend on the Toomre or critical wavelength and the contrast in mass surface density caused by spiral structure. Comparison between our simulations and estimated guiding radii for a few young super-solar metallicity open clusters, including NGC 6583, suggests that the contrast in mass surface density in the solar neighbourhood has standard deviation (in the surface density distribution) divided by mean of about 1/4 and larger than measured using COBE data by Drimmel and Spergel. Our estimate is consistent with a standard deviation of $\sim$0.07 dex in the metallicities measured from high-quality spectroscopic data for 38 young open clusters (<1 Gyr) with mean galactocentric radius 7-9 kpc.

  • The contribution of HI-bearing ultra-diffuse galaxies to the cosmic number density of galaxies.- [PDF] - [Article] - [UPDATED]

    Michael G. Jones, Emmanouil Papastergis, Viraj Pandya, Lukas Leisman, Aaron J. Romanowsky, L. Y. Aaron Yung, Rachel S. Somerville, Elizabeth A. K. Adams

    We estimate the cosmic number density of the recently identified class of HI-bearing ultra-diffuse sources (HUDs) based on the completeness limits of the ALFALFA survey. These objects fall in the range $8.5 < \log M_{\rm{HI}}/\rm{M_{\odot}} < 9.5$, have average $r$-band surface brightnesses fainter than 24 mag arsec$^{-2}$, half-light radii greater than 1.5 kpc, and are separated from neighbours by at least 350 kpc. We find that HUDs contribute at most 6% of the population of HI-bearing dwarfs, have a total cosmic number density of $(1.5 \pm 0.6) \times 10^{-3}$ $\rm{Mpc^{-3}}$, and an HI mass density of $(6.0 \pm 0.8) \times 10^{5}$ $\rm{M_{\odot}\,Mpc^{-3}}$. We estimate that this is similar to the total cosmic number density of UDGs in groups and clusters, and conclude that the relation between the number of UDGs hosted in a halo and the halo mass, must have a break below $M_{200} \sim 10^{12}$ $\rm{M_{\odot}}$ in order to account for the abundance of HUDs. The distribution of the velocity widths of HUDs rises steeply towards low values, indicating a preference for slow rotation rates. These objects have been absent from measurements of the galaxy stellar mass function owing to their low surface brightness. However, we estimate that due to their low number density, their inclusion would constitute a correction of less than 1%. Comparison with the Santa Cruz SAM shows that it produces HI-rich central UDGs that have similar colours to HUDs, but these are currently produced in much great a number. While previous results from this sample have favoured formation scenarios where HUDs form in high spin parameter halos, comparisons with the results of Rong et al. 2017, which invokes that formation mechanism, reveal that this model produces an order of magnitude more field UDGs than we observe in the HUD population.(Abridged)

  • The Second Data Release of the Beijing-Arizona Sky Survey.- [PDF] - [Article] - [UPDATED]

    Hu Zou, Tianmeng Zhang, Zhimin Zhou, Xiyan Peng, Jundan Nie, Xu Zhou, Xiaohui Fan, Linhua Jiang, Ian McGreer, Arjun Dey, Dongwei Fan, Joseph R. Findlay, Jinhua Gao, Yizhou Gu, Yucheng Guo, Boliang He, Junjie Jin, Xu Kong, Dustin Lang, Fengjie Lei, Michael Lesser, Feng Li, Jun Ma, Xiaolei Meng, Moe Maxwell, Adam D. Myers, Liming Rui, David Schlegel, Fengwu Sun, Jiali Wang, Qirong Yuan

    This paper presents the second data release (DR2) of the Beijing-Arizona Sky Survey (BASS). BASS is an imaging survey of about 5400 deg$^2$ in $g$ and $r$ bands using the 2.3 m Bok telescope. DR2 includes the observations as of July 2017 obtained by BASS and Mayall $z$-band Legacy Survey (MzLS). This is our first time to include the MzLS data covering the same area as BASS. BASS and MzLS have respectively completed about 72% and 76% of their observations. The two surveys will be served for the spectroscopic targeting of the upcoming Dark Energy Spectroscopic Instrument. Both BASS and MzLS data are reduced by the same pipeline. We have updated the basic data reduction and photometric methods in DR2. In particular, source detections are performed on stacked images, and photometric measurements are co-added from single-epoch images based on these sources. The median 5$\sigma$ depths with corrections of the Galactic extinction are 24.05, 23.61, and 23.10 mag for $g$, $r$, and $z$ bands, respectively. The DR2 data products include stacked images, co-added catalogs, and single-epoch images and catalogs. The BASS website (this http URL) provides detailed information and links to download the data.

  • Radial Distributions of Surface Mass Density and Mass-to-Luminosity Ratio in Spiral Galaxies.- [PDF] - [Article] - [UPDATED]

    Yoshiaki Sofue

    We present radial profiles of the surface mass density (SMD) in spiral galaxies directly calculated using rotation curves (RC) on two approximations of flat-disk (SMD-F) and spherical mass distribution (SMD-S). The SMDs are combined with surface brightness (SB) using photometric data to derive radial variations of the mass-to-luminosity ratio (ML). It is found that ML has generally a central peak or a plateau, and decreases to a local minimum at $R\sim 0.1-0.2 h$, where $R$ is the radius and $h$ is the scale radius of optical disk. The ML ratio, then, increases rapidly till $\sim 0.5h$, and is followed by gradual rise till $\sim 2h$, remaining at around ML$\sim 2$ in w1 band (infrared $\lambda$ 3.4 $\mu$m) and $\sim 10\ [M_\odot L_\odot^{-1}]$ in r-band ($\lambda$6200-7500 A). Beyond this radius, ML steeply increases toward the observed edges at $R\sim 5h$, attaining values as high as ML$\sim 20$ in w1 and $\sim 10^2\ [M_\odot L_\odot^{-1}]$ in r-band, indicative of dominant dark matter. The general properties of the ML distributions will be useful to constrain cosmological formation models of spiral galaxies. The radial profiles of the RC, SMD, and ML are available in pdf/eps figures and machine-readable tables as an archival atlas at URL this http URL and as the supplementary data on PASJ home page.

  • Jeans Instability in a Universe with Dissipation.- [PDF] - [Article] - [UPDATED]

    G.M.Kremer, M.G. Richarte, F. Teston

    The problem of Jeans gravitational instability is investigated for static and expanding universes within the context of the five and thirteen field theories which account for viscous and thermal effects. For the five-field theory a general dispersion relation has been derived with the help of relevant linearized perturbation equations, showing that the shear viscosity parameter alters the propagating modes for large and small wavelengths. The behavior of density and temperature contrasts are analyzed for the hard-sphere model in detail. In the small wavelengths regime, increasing the amount of shear viscosity into the system forces the harmonic perturbations to damp faster, however, in the opposite limit larger values of shear viscosity lead to smaller values of density and temperature contrasts. For the hyperbolic case, the dispersion relation becomes a polynomial in the frequency with two orders higher in relation to the five-field theory, indicating that the effects associated with the shear viscosity and heat flux are non-trivial. The profile of Jeans mass in terms of the temperature and number density is explored by contrasting with several data of molecular clouds. Regarding the dynamical evolution of the density, temperature, stress and heat flux contrasts for a universe dominated by pressureless matter, we obtain also damped harmonic waves for small wavelengths. In the case of large wavelengths, the density and temperature contrasts grow with time (due to the Jeans mechanism) while the stress and heat flux contrasts heavily decay with time.


  • Nonparametric Methods in Astronomy: Think, Regress, Observe -- Pick Any Three.- [PDF] - [Article]

    Charles L. Steinhardt, Adam S. Jermyn

    Telescopes are much more expensive than astronomers, so it is essential to minimize required sample sizes by using the most data-efficient statistical methods possible. However, the most commonly used model-independent techniques for finding the relationship between two variables in astronomy are flawed. In the worst case they can lead without warning to subtly yet catastrophically wrong results, and even in the best case they require more data than necessary. Unfortunately, there is no single best technique for nonparametric regression. Instead, we provide a guide for how astronomers can choose the best method for their specific problem and provide a python library with both wrappers for the most useful existing algorithms and implementations of two new algorithms developed here.

  • Precision Projector Laboratory: Detector Characterization with an Astronomical Emulation Testbed.- [PDF] - [Article]

    Charles Shapiro, Roger Smith, Eric Huff, Andrés A. Plazas, Jason Rhodes, Jason Fucik, Tim Goodsall, Richard Massey, Barnaby Rowe, Suresh Seshadri

    As astronomical observations from space benefit from improved sensitivity, the effectiveness of scientific programs is becoming limited by systematics that often originate in poorly understood image sensor behavior. Traditional, bottom-up detector characterization methods provide one way to model underlying detector physics, and generate ever more faithful numerical simulations, but this approach is vulnerable to preconceptions and over-simplification. The alternative top-down approach is laboratory emulation, which enables observation, calibration, and analysis scenarios to be tested without relying on a complete understanding of the underlying physics. This complements detector characterization and simulation efforts by testing their validity. We describe a laboratory facility and experimental testbed that supports the emulation of a wide range of mission concepts such as gravitational weak lensing measurements by WFIRST and high precision spectrophotometry of transiting exoplanets by JWST. An Offner relay projects readily customizable "scenes" (e.g. stars, galaxies, spectra) with very low optical aberration over the full area of a typical optical or near infrared image sensor. f/8 and slower focal ratios may be selected, spanning those of most proposed space missions and approximating the point spread function (PSF) size of seeing limited ground based surveys. Diffraction limited PSFs are projected over a wide field of view and wavelength range to deliver highly predictable image patterns down to sub-pixel scales with stable intensity and fine motion control. The testbed enables realistic validation of detector performance on science-like images, which aids mission design and survey strategy, as well as targeted investigations of various detector effects.

  • Status and performance of the THD2 bench in multi-deformable mirror configuration.- [PDF] - [Article]

    Pierre Baudoz, Raphael Galicher, Fabien Patru, Olivier Dupuis, Simone Thijs

    The architecture of exoplanetary systems is relatively well known inward to 1 AU thanks to indirect techniques, which have allowed characterization of thousands of exoplanet orbits, masses and sometimes radii. The next step is the characterization of exoplanet atmospheres at long period, which requires direct imaging capability. While the characterization of a handful of young giant planets is feasible with dedicated instruments like SPHERE/VLT, GPI/Gemini, SCExAO/Subaru and soon with the coronagraphic capabilities aboard JWST, the spectroscopic study of mature giant planets and lower mass planets (Neptune-like, Super Earths) requires the achievement of better coronagraphic performance. While space-based coronagraph on WFIRST-AFTA might start this study at low spectroscopic resolution, dedicated projects on large space telescope and on the ELT will be required for a more complete spectroscopic study of these faint planets. To prepare these future instruments, we developed a high contrast imaging bench called THD, then THD2 for the upgraded version using multi-DM configuration. The THD2 bench is designed to test and compare coronagraphs as well as focal plane wavefront sensors and wavefront control techniques. It can simulate the beam provided by a space telescope and soon the first stage of adaptive optics behind a ground-based telescope. In this article, we describe in details the THD2 bench and give the results of a recent comparison study of the chromatic behavior for several coronagraph on the THD2.

  • Peak-locking centroid bias in Shack-Hartmann wavefront sensing.- [PDF] - [Article]

    Narsireddy Anugu, Paulo J. V. Garcia, Carlos M. Correia

    Shack-Hartmann wavefront sensing relies on accurate spot centre measurement. Several algorithms were developed with this aim, mostly focused on precision, i.e. minimizing random errors. In the solar and extended scene community, the importance of the accuracy (bias error due to peak-locking, quantisation or sampling) of the centroid determination was identified and solutions proposed. But these solutions only allow partial bias corrections. To date, no systematic study of the bias error was conducted. This article bridges the gap by quantifying the bias error for different correlation peak-finding algorithms and types of sub-aperture images and by proposing a practical solution to minimize its effects. Four classes of sub-aperture images (point source, elongated laser guide star, crowded field and solar extended scene) together with five types of peak-finding algorithms (1D parabola, the centre of gravity, Gaussian, 2D quadratic polynomial and pyramid) are considered, in a variety of signal-to-noise conditions. The best performing peak-finding algorithm depends on the sub-aperture image type, but none is satisfactory to both bias and random errors. A practical solution is proposed that relies on the anti-symmetric response of the bias to the sub-pixel position of the true centre. The solution decreases the bias by a factor of ~7 to values of < 0.02 pix. The computational cost is typically twice of current cross-correlation algorithms.

  • The Soft X-ray Imager (SXI) aboard Hitomi (ASTRO-H).- [PDF] - [Article]

    Takaaki Tanaka, Hiroyuki Uchida, Hiroshi Nakajima, Hiroshi Tsunemi, Kiyoshi Hayashida, Takeshi G. Tsuru, Tadayasu Dotani, Ryo Nagino, Shota Inoue, Shohei Katada, Ryosaku Washino, Masanobu Ozaki, Hiroshi Tomida, Chikara Natsukari, Shutaro Ueda, Masachika Iwai, Koji Mori, Makoto Yamauchi, Isamu Hatsukade, Yusuke Nishioka, Eri Isoda, Masayoshi Nobukawa, Junko S. Hiraga, Takayoshi Kohmura, Hiroshi Murakami, Kumiko K. Nobukawa, Aya Bamba, John P. Doty

    The Soft X-ray Imager (SXI) is an imaging spectrometer using charge-coupled devices (CCDs) aboard the Hitomi X-ray observatory. The SXI sensor has four CCDs with an imaging area size of $31~{\rm mm} \times 31~{\rm mm}$ arranged in a $2 \times 2$ array. Combined with the X-ray mirror, the Soft X-ray Telescope, the SXI detects X-rays between $0.4~{\rm keV}$ to $12~{\rm keV}$ and covers a $38^{\prime} \times 38^{\prime}$ field-of-view. The CCDs are P-channel fully-depleted, back-illumination type with a depletion layer thickness of $200~\mu{\rm m}$. Low operation temperature down to $-120~^\circ{\rm C}$ as well as charge injection is employed to reduce the charge transfer inefficiency of the CCDs. The functionality and performance of the SXI are verified in on-ground tests. The energy resolution measured is $161$-$170~{\rm eV}$ in full width at half maximum for $5.9~{\rm keV}$ X-rays. In the tests, we found that the CTI of some regions are significantly higher. A method is developed to properly treat the position-dependent CTI. Another problem we found is pinholes in the Al coating on the incident surface of the CCDs for optical light blocking. The Al thickness of the contamination blocking filter is increased in order to sufficiently block optical light.

  • Measurement of low-energy background events due to $^{222}$Rn contamination on the surface of a NaI(Tl) crystal.- [PDF] - [Article]

    K.W. Kim, C. Ha, N.Y. Kim, Y.D. Kim, H.S. Lee, B.J. Park, H.K. Park

    It has been known that decays of $^{222}$Rn and its daughter elements on the surface of a detector cause significant background at energies below 10~keV. In particular $^{210}$Pb and $^{210}$Po decays on the crystal surface result in significant background for dark matter search experiments with NaI(Tl) crystals. In this report, measurement of $^{210}$Pb and $^{210}$Po decays on surfaces are obtained by using a $^{222}$Rn contaminated crystal. Alpha decay events on the surface of $^{210}$Pb are measured by coincidence requirements of two attached crystals. Due to recoiling of $^{206}$Pb, rapid nuclear recoil events are observed. A mean time characterization demonstrates that $^{206}$Pb recoil events are distinct from those of sodium or iodine nuclear recoil events, as well as electron recoil events.

  • Commercialization of micro-fabrication of antenna-coupled Transition Edge Sensor bolometer detectors for studies of the Cosmic Microwave Background.- [PDF] - [Article]

    Aritoki Suzuki, Chris Bebek, Maurice Garcia-Sciveres, Stephen Holland, Akito Kusaka, Adrian T. Lee, Nicholas Palaio, Natalie Roe, Leo Steinmetz

    We report on the development of commercially fabricated multi-chroic antenna coupled Transition Edge Sensor (TES) bolometer arrays for Cosmic Microwave Background (CMB) polarimetry experiments. CMB polarimetry experiments have deployed instruments in stages. Stage-II experiments deployed with O(1,000) detectors and reported successful detection of B-mode (divergent free) polarization pattern in the CMB. Stage-III experiments have recently started observing with O(10,000) detectors with wider frequency coverage. A concept for a Stage-IV experiment, CMB-S4, is emerging to make a definitive measurement of CMB polarization from the ground with O(400,000) detectors. The orders of magnitude increase in detector count for CMB-S4 requires a new approach in detector fabrication to increase fabrication throughput.and reduce cost. We report on collaborative efforts with two commercial micro-fabrication foundries to fabricate antenna coupled TES bolometer detectors. The detector design is based on the sinuous antenna coupled dichroic detector from the POLARBEAR-2 experiment. The TES bolometers showed the expected I-V response and the RF performance agrees with simulation. We will discuss the motivation, design consideration, fabrication processes, test results, and how industrial detector fabrication could be a path to fabricate hundreds of detector wafers for future CMB polarimetry experiments.

  • Excitation and charge transfer in low-energy hydrogen atom collisions with neutral iron.- [PDF] - [Article]

    P. S. Barklem

    Data for inelastic processes due to hydrogen atom collisions with iron are needed for accurate modelling of the iron spectrum in late-type stars. Excitation and charge transfer in low-energy Fe+H collisions is studied theoretically using a previously presented method based on an asymptotic two-electron linear combination of atomic orbitals (LCAO) model of ionic-covalent interactions in the neutral atom-hydrogen-atom system, together with the multi-channel Landau-Zener model. An extensive calculation including 166 covalent states and 25 ionic states is presented and rate coefficients are calculated for temperatures in the range 1000 - 20000 K. The largest rates are found for charge transfer processes to and from two clusters of states around 6.3 and 6.6 eV excitation, corresponding in both cases to active 4d and 5p electrons undergoing transfer. Excitation and de-excitation processes among these two sets of states are also significant.

  • Identification and mitigation of narrow spectral artifacts that degrade searches for persistent gravitational waves in the first two observing runs of Advanced LIGO.- [PDF] - [Article]

    P. B. Covas, A. Effler, E. Goetz, P. M. Meyers, A. Neunzert, M. Oliver, B. L. Pearlstone, V. J. Roma, R. M. S. Schofield, V. B. Adya, P. Astone, S. Biscoveanu, T. A. Callister, N. Christensen, A. Colla, E. Coughlin, M. W. Coughlin, S. G. Crowder, S. E. Dwyer, S. Hourihane, S. Kandhasamy, W. Liu, A. P. Lundgren, A. Matas, R. McCarthy, J. McIver, G. Mendell, R. Ormiston, C. Palomba, O. J. Piccinni, K. Rao, K. Riles, L. Sammut, S. Schlassa, D. Sigg, N. Strauss, D. Tao, K. A. Thorne, E. Thrane, S. Trembath-Reichert, B. P. Abbott, R. Abbott, T. D. Abbott, C. Adams, R. X. Adhikari, A. Ananyeva, S. Appert, K. Arai, S. M. Aston, C. Austin, S. W. Ballmer, D. Barker, B. Barr, L. Barsotti, J. Bartlett, I. Bartos, J. C. Batch, M. Bejger, A. S. Bell, J. Betzwieser, G. Billingsley, J. Birch, S. Biscans, et al. (200 additional authors not shown)

    Searches are under way in Advanced LIGO and Virgo data for persistent gravitational waves from continuous sources, e.g. rapidly rotating galactic neutron stars, and stochastic sources, e.g. relic gravitational waves from the Big Bang or superposition of distant astrophysical events such as mergers of black holes or neutron stars. These searches can be degraded by the presence of narrow spectral artifacts (lines) due to instrumental or environmental disturbances. We describe a variety of methods used for finding, identifying and mitigating these artifacts, illustrated with particular examples. Results are provided in the form of lists of line artifacts that can safely be treated as non-astrophysical. Such lists are used to improve the efficiencies and sensitivities of continuous and stochastic gravitational wave searches by allowing vetoes of false outliers and permitting data cleaning.

  • ChromaStarPy: A stellar atmosphere and spectrum modeling and visualization lab in python.- [PDF] - [Article]

    C. Ian Short, Jason H.T. Bayer, Lindsey M. Burns

    We announce ChromaStarPy, an integrated general stellar atmospheric modeling and spectrum synthesis code written entirely in python V. 3. ChromaStarPy is a direct port of the ChromaStarServer (CSServ) Java modeling code described in earlier papers in this series, and many of the associated JavaScript (JS) post-processing procedures have been ported and incorporated into CSPy so that students have access to ready-made "data products". A python integrated development environment (IDE) allows a student in a more advanced course to experiment with the code and to graphically visualize intermediate and final results, ad hoc, as they are running it. CSPy allows students and researchers to compare modeled to observed spectra in the same IDE in which they are processing observational data, while having complete control over the stellar parameters affecting the synthetic spectra. We also take the opportunity to describe improvements that have been made to the related codes, ChromaStar (CS), CSServ and ChromaStarDB (CSDB) that, where relevant, have also been incorporated into CSPy. The application may be found at the home page of the OpenStars project: this http URL .

  • Automated reliability assessment for spectroscopic redshift measurements.- [PDF] - [Article] - [UPDATED]

    S. Jamal, V. Le Brun, O. Le Fèvre, D. Vibert, A. Schmitt, C. Surace, Y. Copin, B. Garilli, M. Moresco, L. Pozzetti

    We present a new approach to automate the spectroscopic redshift reliability assessment based on machine learning (ML) and characteristics of the redshift probability density function (PDF). We propose to rephrase the spectroscopic redshift estimation into a Bayesian framework, in order to incorporate all sources of information and uncertainties related to the redshift estimation process, and produce a redshift posterior PDF that will be the starting-point for ML algorithms to provide an automated assessment of a redshift reliability. As a use case, public data from the VIMOS VLT Deep Survey is exploited to present and test this new methodology. We first tried to reproduce the existing reliability flags using supervised classification to describe different types of redshift PDFs, but due to the subjective definition of these flags, soon opted for a new homogeneous partitioning of the data into distinct clusters via unsupervised classification. After assessing the accuracy of the new clusters via resubstitution and test predictions, unlabelled data from preliminary mock simulations for the Euclid space mission are projected into this mapping to predict their redshift reliability labels.


  • Cosmic no-hair in spherically symmetric black hole spacetimes.- [PDF] - [Article]

    João L. Costa, Pedro Oliveira, José Natário

    We analyze in detail the geometry and dynamics of the cosmological region arising in spherically symmetric black hole solutions of the Einstein-Maxwell-scalar field system with a positive cosmological constant. More precisely, we solve, for such a system, a characteristic initial value problem with data emulating a dynamic cosmological horizon. Our assumptions are fairly weak, in that we only assume that the data approaches that of a subextremal Reissner-Nordstr\"om-de Sitter black hole, without imposing any rate of decay. We then show that the radius (of symmetry) blows up along any null ray parallel to the cosmological horizon ("near" $i^+$), in such a way that $r=+\infty$ is, in an appropriate sense, a spacelike hypersurface. We also prove a version of the Cosmic No-Hair Conjecture by showing that in the past of any causal curve reaching infinity both the metric and the Riemann curvature tensor asymptote those of a de Sitter spacetime. Finally, we discuss conditions under which all the previous results can be globalized.

  • On the asymptotic behavior of static perfect fluids.- [PDF] - [Article]

    Lars Andersson, Annegret Y. Burtscher

    Static spherically symmetric solutions to the Einstein-Euler equations with prescribed central densities are known to exist, be unique and smooth for reasonable equations of state. Some criteria are also available to decide whether solutions have finite extent (stars with a vacuum exterior) or infinite extent. In the latter case, the matter extends globally with the density approaching zero at infinity. The asymptotic behavior largely depends on the equation of state of the fluid and is still poorly understood. While a few such unbounded solutions are known to be asymptotically flat with finite ADM mass, the vast majority are not. We provide a full geometric description of the asymptotic behavior of static spherically symmetric perfect fluid solutions with linear and polytropic-type equations of state. In order to capture the asymptotic behavior we introduce a notion of scaled quasi-asymptotic flatness, which encodes a form of asymptotic conicality. In particular, these spacetimes are asymptotically simple.

  • Superconducting fluctuation current caused by gravitational drag.- [PDF] - [Article]

    Satoshi Tsuchida, Hiroshi Kuratsuji

    We examine a possible effect of the Lense--Thirring field or gravitational drag by calculating the fluctuation current through a superconducting ring. The gravitational drag is induced by a rotating sphere, on top of which the superconducting ring is placed. The formulation is based on the Landau-Ginzburg free energy functional of linear form. The resultant fluctuation current is shown to be greatly enhanced in the vicinity of the transition temperature, and the current also increases on increasing the winding number of the ring. These effects would provide a modest step towards magnification of tiny gravity.

  • Exact ghost-free bigravitational waves.- [PDF] - [Article]

    Eloy Ayón-Beato, Daniel Higuita-Borja, Julio A. Méndez-Zavaleta, Gerardo Velázquez-Rodríguez

    We study the propagation of exact gravitational waves in the ghost-free bimetric theory. Our focus is on type N spacetimes compatible with the cosmological constants provided by the bigravity interaction potential, and particularly in the single class known by allowing at least a Killing symmetry: the AdS waves. They have the advantage of being represented by a generalized Kerr-Schild transformation from AdS spacetime. This means a notorious simplification in bigravity by allowing to straightforwardly compute any power of its interaction square root matrix, opening the door to explore physically meaningful exact configurations. For these exact gravitational waves the complex dynamical structure of bigravity decomposes into elementary exact massless or massive excitations propagating on AdS. We use a complexified formulation of the Euler-Darboux equations to provide for the first time the general solutions to the massive version of the Siklos equation which rules the resulting AdS-waves dynamics, using an integral representation originally due to Poisson. Inspired in this progress we tackle the subtle problem on how matter couples to bigravity and concretely if this occurs through a composite metric, which is hard to handle in a general setting. Surprisingly, the Kerr-Schild ansatz brings again a huge simplification in how the related energy-momentum tensors are calculated. This allows us to explicitly characterize AdS waves supported in one case by a massless free scalar field and by a wavefront-homogeneous Maxwell field in another. Considering the most general allowed Maxwell source instead is a highly nontrivial task, that we accomplish by exploiting again the complexified Euler-Darboux description and taking advantage of the classical Riemann method. In fact, this allow us to find at the end the most general configurations for any matter source.

  • Saha Equation for the Photo-Ionization of Hydrogen Atoms in Partially Ionized Relativistic Hydrogen Plasma and the Effect of Gravity on the Binding of Hydrogen Atoms in Rindler Space.- [PDF] - [Article]

    Sanchita Das, Somenath Chakrabarty

    We have studied Saha equation for photo-ionization of hydrogen atoms in partially ionized relativistic hydrogen plasma in Rindler space. Following the principle of equivalence, we have obtained the abundances of neutral hydrogen atoms, hydrogen ions and the electrons in dynamic equilibrium of the photo-ionization reaction of neutral hydrogen atoms and electron capture process by hydrogen ions (de-ionization process) and also investigated their variations with temperature of the plasma and the uniform gravitational field in the Rindler space or equivalently the uniform acceleration of the observer. Hence obtained the Saha ionization formula for partially ionized hydrogen plasma in Rindler space. It has been observed that the abundance of neutral hydrogen atoms decreases with the increase in temperature of the plasma, which is the usual picture, whereas it increases with the increases in the strength of uniform gravitational field. The second part of this observation shows that the binding of the electrons inside hydrogen atoms increases with the increase in the strength of gravitational field or equivalently an observer with very high acceleration will see less amount of ionized hydrogen atoms compared to inertial observer.

  • Cosmological Theories Of The Extra Terms.- [PDF] - [Article]

    A. M. Deakin, L. H. Kauffman

    This paper purports to have: Introduced a new formulation of Quantum Mechanics, explained the apparent disconnect between Quantum Mechanics and General Relativity, explained the observed far field expansion of the Universe (Dark Energy), supplied an argument which goes towards explaining away Dark Matter (there are modelling difficulties) and not explained, on the basis of gravitational theory, the Voyager Anomaly.

  • Accelerating AdS black holes as the holographic heat engines in a benchmarking scheme.- [PDF] - [Article]

    Jialin Zhang, Yanjun Li, Hongwei Yu

    We investigate the properties of holographic heat engines with an accelerating non-rotating AdS black hole as the working substance in a benchmarking scheme. In the case of uncharged accelerating black holes, we find that the efficiencies of the black hole heat engines can be influenced by both the size of the benchmark circular cycle and the cosmic string tension as a thermodynamic variable.For the general case of charged accelerating black holes, we show that the existence of charge may significantly increase the efficiencies of the black hole heat engines and make them be more sensitive to a varying cosmic string tension. A cross-comparison of the efficiencies of different black hole heat engines suggests that the acceleration also increases the efficiency and renders it more sensitive as the charge varies.

  • Introduction to teleparallel gravities.- [PDF] - [Article]

    Alexey Golovnev

    We give a pedagogical introduction into the field of (modified) teleparallel theories of gravity. Our presentation is fairly self-contained. In particular, we carefully explain the basic principles of metric-affine approaches to gravity. This contribution is based on our talk "Teleparallel gravity, its modifications, and the local Lorentz invariance" at the 9th Mathematical Physics Meeting: School and Conference on Modern Mathematical Physics in Belgrade, September 2017.

  • Multipole analysis in the radiation field for linearized $f(R)$ gravity with irreducible Cartesian tensors.- [PDF] - [Article]

    Bofeng Wu, Chao-Guang Huang

    The $1/r$-expansion in the distance to the source is applied to the linearized $f(R)$ gravity, and its multipole expansion in the radiation field with irreducible Cartesian tensors is presented. Then, the energy, momentum, and angular momentum in the gravitational waves are provided for linearized $f(R)$ gravity. All of these results have two parts which are associated with the tensor part and the scalar part in the multipole expansion of linearized $f(R)$ gravity, respectively. The former is the same as that in General Relativity, and the latter, as the correction to the result in General Relativity, is caused by the massive scalar degree of freedom, and places an important role in distinguishing GR and $f(R)$ gravity.

  • Dynamics of marginally trapped surfaces in a binary black hole merger: Growth and approach to equilibrium.- [PDF] - [Article]

    Anshu Gupta, Badri Krishnan, Alex Nielsen, Erik Schnetter

    The behavior of quasi-local black hole horizons in a binary black hole merger is studied numerically. We compute the horizon multipole moments, fluxes and other quantities on black hole horizons throughout the merger. These lead to a better qualitative and quantitative understanding of the coalescence of two black holes; how the final black hole is formed, initially grows and then settles down to a Kerr black hole. We calculate the rate at which the final black hole approaches equilibrium in a fully non-perturbative situation and identify a time at which the linear ringdown phase begins. Finally, we provide additional support for the conjecture that fields at the horizon are correlated with fields in the wave-zone by comparing the in-falling gravitational wave flux at the horizon to the outgoing flux as estimated from the gravitational waveform.

  • Advanced Lectures in General Relativity.- [PDF] - [Article]

    Geoffrey Compère, Adrien Fiorucci

    These lecture notes are intended for starting PhD students in theoretical physics who have a working knowledge of General Relativity. The 4 topics covered are (1) Surface charges as conserved quantities in theories of gravity; (2) Classical and holographic features of three-dimensional Einstein gravity; (3) Asymptotically flat spacetimes in 4 dimensions: BMS group and memory effects; (4) The Kerr black hole: properties at extremality and quasi-normal mode ringing. Each topic starts with historical foundations and points to a few modern research directions.

  • Cosmological solutions from models with unified dark energy and dark matter and with inflaton field.- [PDF] - [Article]

    Denitsa Staicova, Michail Stoilov

    Recently, few cosmological models with additional non-Riemannian volume form(s) have been proposed. In this article we use Supernovae type Ia experimental data to test one of these models which provides a unified description of both dark energy via dynamically generated cosmological constant and dark matter as a "dust" fluid due to a hidden nonlinear Noether symmetry. It turns out that the model allows various scenarios of the future Universe evolution and in the same time perfectly fits contemporary observational data. Further, we investigate the influence of an additional inflaton field with a step like potential. With its help we can reproduce the Universe inflation epoch, matter dominated epoch and present accelerating expansion in a seamless way. Interesting feature is that inflaton undergoes a finite change during its evolution. It can be speculated that the inflaton asymptotic value is connected to the vacuum expectation value of the Higgs field.

  • Black hole interior in Painleve-Gullstrand coordinates.- [PDF] - [Article]

    Hristu Culetu

    A nonstatic Schwarzschild black hole interior solution in Painleve-Gullstrand coordinates is proposed in this paper, by means of a coordinate transformation that changes the spatial coordinate but the timelike one is preserved. The timelike and null geodesic equations are obtained exactly, taking advantage that the spatial z-coordinate is cyclic.

  • On the Cosmological Frame Problem.- [PDF] - [Article]

    Sotirios Karamitsos, Apostolos Pilaftsis

    We introduce a fully-frame covariant formalism for inflation by taking into account conformal transformations in addition to field reparametrizations. We begin by providing a brief overview of frame problems in the history of science before outlining the crux of the frame problem in inflationary cosmology. After introducing the concept of frame tensors in curved field space, we demonstrate how the quantum perturbations and the observables sourced by them can be made frame covariant. We then specialize to two-field models, examining the impact of isocurvature effects on the inflationary observables in a frame-covariant manner. We study the phenomenology of two particular models, a minimal polynomial model and a nonminimal model inspired by Higgs inflation. We observe that in the latter scenario, isocurvature effects are greatly enhanced. Moving beyond the tree-level approximation, we outline how our approach may be extended at the quantum level through the Vilkovisky--De Witt formalism and the generalization of frame tensors to configuration space, leading to a fully frame-invariant effective action. Finally, we summarize our findings and present possible future directions of research on the topic of frame covariance.

  • Timelets on causal sets.- [PDF] - [Article]

    Roman Zapatrin

    Dual structures on causal sets called timelets are introduced, being discrete analogs of global time coordinates. Geometrical and algebraic features of the set of timelets on a causal set are studied.

  • Scalar Casimir effect in a linearly expanding universe.- [PDF] - [Article]

    A. A. Saharian, T. A. Petrosyan, S. V. Abajyan, B. B. Nersisyan

    We investigate quantum vacuum effects for a massive scalar field, induced by two planar boundaries in background of a linearly expanding spatially flat Friedmann-Robertson-Walker spacetime for an arbitrary number of spatial dimensions. For the Robin boundary conditions and for general curvature coupling parameter, a complete set of mode functions is presented and the related Hadamard function is evaluated. The results are specified for the most important special cases of the adiabatic and conformal vacuum states. The vacuum expectation values of the field squared and of the energy-momentum tensor are investigated for a massive conformally coupled field. The vacuum energy-momentum tensor, in addition to the diagonal components, has nonzero off-diagonal component describing energy flux along the direction perpendicular to the plates. The influence of the gravitational field on the local characteristics of the vacuum state is essential at distances from the boundaries larger than the curvature radius of the background spacetime. In contrast to the Minkowskian bulk, at large distances the boundary-induced expectation values follow as power law for both massless and massive fields. Another difference is that the Casimir forces acting on the separate plates do not coincide if the corresponding Robin coefficients are different. At large separations between the plates the decay of the forces is power law. We show that during the cosmological expansion the forces may change the sign.

  • Axisymmetric black holes allowing for separation of variables in the Klein-Gordon and Hamilton-Jacobi equation.- [PDF] - [Article]

    R. A. Konoplya, Z. Stuchlik, A. Zhidenko

    We determine the class of axisymmetric and asymptotically flat black-hole spacetimes for which the test Klein-Gordon and Hamilton-Jacobi equations allow for the separation of variables. The known Kerr, Kerr-Newman, Kerr-Sen and some other black-hole metrics are within the described here class of spacetimes. It is shown that although the black-hole metric in the Einstein-dilaton-Gauss-Bonnet theory does not allow for the separation of variables (at least in the considered coordinates), for a number of applications it can be effectively approximated by a metric within the above class. This gives us some hope that the described here class of spacetimes may be not only a generic for the known solutions, for which the variables can be separated in the Klein-Gordon and Hamilton-Jacobi equations, but also a good approximation for a broader class of metrics, which does not allow for such a separation. Finally, the generic form of the axisymmetric metric is expanded in the radial direction in terms of the continued fractions and the connection with other black-hole parameterizations is discussed.

  • Looking for a new test of general relativity in the solar system.- [PDF] - [Article]

    Angelo Tartaglia, Giampiero Esposito, Emmanuele Battista, Simone Dell'Agnello, Bin Wang

    This paper discusses three matter-of-principle methods for measuring the general relativity correction to the Newtonian values of the position of collinear Lagrangian points L1 and L2 of the Sun-Earth-satellite system. All approaches are based on time measurements. The first approach exploits a pulsar emitting signals and two receiving antennas located at L1 and L2, respectively. The second method is based on a relativistic positioning system based on the Lagrangian points themselves. These first two methods depend crucially on the synchronization of clocks at L1 and L2. The third method combines a pulsar and an artificial emitter at the stable points L4 or L5 forming a basis for the positioning of the collinear points L1 and L2. Further possibilities are mentioned and the feasibility of the measurements is considered.

  • Electro-Magnetic Space-Time Duality for 2+1-Dimensional Stationary Classical Solutions. (arXiv:hep-th/0601218v2 UPDATED)

    P. Castelo Ferreira

    In this paper it is studied a space-time duality web that maps electric into magnetic (and magnetic into electric) charged classical stationary rotating solutions for $2+1$-dimensional Abelian Einstein Maxwell Chern-Simons theories. A first duality map originally suggested by Kogan for static charged solutions is extended to stationary rotating space-times and are suggested two new space-time dualities maps. The three dualities complete a close duality web. It is also shown that in $3+1$-dimensions these dualities are only possible for systems which exhibit non-projected cylindrical symmetry and are not related to the standard electromagnetic duality of Maxwell equations which acts on the physical fields and charges. Generalization to $N$-form theories in higher dimensional space-times is briefly discussed.

  • How can geometric calculus enable us to express Berezin integral in terms of Riemann sums.- [PDF] - [Article] - [UPDATED]

    Roman Sverdlov

    Berezin integral is commonly viewed as a purely formal operation. In this paper, however, we show that, by means of geometric calculus, we are able to express Berezin integral as a Riemann sum thus making it ontologically similar to other types of integrals. In particular, the fact that geometric calculus has two types of product (anticommuting wedge product and also Clifford product) enables us, at least in principle, to have Riemann sum that would return real or complex number. Apart from that, our Riemann sum corresponds to an integral over a surface in a space of very high dimension; we then claim that the fact that Berezin integral coincides with derivative is a consequence of divergence theorem. The multiple integrals will work as desired in the limit of the dimensionality of the space going to infinity. On the other hand, if dimensionality is finite, we will get a sufficiently close approximation to Berezin integral if the dimensionality is much larger than the number of interactions of the integrals.

  • Quantum correction to the entropy of noncommutative BTZ black hole.- [PDF] - [Article] - [UPDATED]

    M. A. Anacleto, F. A. Brito, E. Passos, A. G. Cavalcanti, J. Spinelly

    In this paper we consider the generalized uncertainty principle (GUP) in the tunneling formalism via Hamilton-Jacobi method to determine the quantum-corrected Hawking temperature and entropy for noncommutative BTZ black hole. In our results we obtain several types of corrections including the expected logarithmic correction to the area entropy associated with the noncommutative BTZ black holes. We also show that the area entropy product of the noncommutative BTZ black holes is dependent on mass and by analyzing the nature of the specific heat capacity we have observed that the noncommutative BTZ black hole is stable at some range of parameters.

  • Pre-big bang geometric extensions of inflationary cosmologies.- [PDF] - [Article] - [UPDATED]

    David Klein, Jake Reschke

    Robertson-Walker spacetimes within a large class are geometrically extended to larger cosmologies that include spacetime points with zero and negative cosmological times. In the extended cosmologies, the big bang is lightlike, and though singular, it inherits some geometric structure from the original spacetime. Spacelike geodesics are continuous across the cosmological time zero submanifold which is parameterized by the radius of Fermi space slices, i.e, by the proper distances along spacelike geodesics from a comoving observer to the big bang. The continuous extension of the metric, and the continuously differentiable extension of the leading Fermi metric coefficient $g_{\tau\tau}$ of the observer, restrict the geometry of spacetime points with pre-big bang cosmological time coordinates. In our extensions the big bang is two dimensional in a certain sense, consistent with some findings in quantum gravity.

  • Generalized thermalization for integrable system under quantum quench.- [PDF] - [Article] - [UPDATED]

    Sushruth Muralidharan, Kinjalk Lochan, S. Shankaranarayanan

    We investigate equilibration and generalized thermalization of the quantum Harmonic chain under local quantum quench. The quench action we consider is connecting two disjoint harmonic chains of different sizes and the system jumps between two integrable settings. We verify the validity of the Generalized Gibbs Ensemble description for this infinite dimensional Hilbert space system and also identify equilibration between the subsystems as in classical systems. Using Bogoliubov transformations, we show that the eigenstates of the system prior to the quench evolve towards the Gibbs Generalized Ensemble description. Eigenstates that are more delocalized (in the sense of inverse participation ratio) prior to the quench, tend to equilibrate more rapidly. Further, through the phase space properties of a Generalized Gibbs Ensemble and the strength of stimulated emission, we identify the necessary criterion on the initial states for such relaxation at late times and also find out the states which would potentially not be described by the Gibbs Generalized Ensemble description.

  • A continuous Riemann-Hilbert problem for colliding plane gravitational waves.- [PDF] - [Article] - [UPDATED]

    Stefan Palenta, Reinhard Meinel

    We present the foundations of a new solution technique for the characteristic initial value problem (IVP) of colliding plane gravitational waves. It has extensive similarities to the approach of Alekseev and Griffiths in 2001, but we use an inverse scattering method with a Riemann-Hilbert problem (RHP), which allows for a transformation to a continuous RHP with a solution given in terms of integral equations for non-singular functions. Ambiguities in this procedure lead to the construction of a family of spacetimes containing the solution to the IVP. Therefore the described technique also serves as an interesting solution generating method. The procedure is exemplified by extending the Szekeres class of colliding wave spacetimes with 2 additional real parameters. The obtained solution seems to feature a limiting case of a new type of impulsive waves, which are circularly polarised.

  • The zeroth law in quasi-homogeneous thermodynamics and black holes.- [PDF] - [Article] - [UPDATED]

    Alessandro Bravetti, Christine Gruber, Cesar S. Lopez-Monsalvo, Francisco Nettel

    Motivated by black holes thermodynamics, we consider the zeroth law of thermodynamics for systems whose entropy is a quasi-homogeneous function of the extensive variables. We show that the generalized Gibbs-Duhem identity and the Maxwell construction for phase coexistence based on the standard zeroth law are incompatible in this case. We argue that the generalized Gibbs-Duhem identity suggests a revision of the zeroth law which in turns permits to reconsider Maxwell's construction in analogy with the standard case. The physical feasibility of our proposal is considered in the particular case of black holes.

  • Gravitational wave spectroscopy of binary neutron star merger remnants with mode stacking.- [PDF] - [Article] - [UPDATED]

    Huan Yang, Vasileios Paschalidis, Kent Yagi, Luis Lehner, Frans Pretorius, Nicolas Yunes

    A binary neutron star (BNS) merger event has recently been observed in gravitational waves (GWs). As in the case of binary black holes, GWs generated by BNS consist of inspiral, merger, and post-merger components. Detecting the latter is important because it encodes information about the nuclear equation of state (EOS) in a regime that cannot be probed prior to merger. The post-merger signal, however, can be observed by current detectors only out to~ 10 Mpc. We carry out Monte-Carlo simulations showing that the dominant post-merger signal (the 22 mode) from individual events will likely not be observable even with the Einstein Telescope and Cosmic Explorer (CE), assuming a full year of operation, the latest merger rates, and a detection threshold with signal-to-noise ratio of 5. For this reason, we propose two methods that stack the post-merger signal from multiple events to boost the detection probability. The first method follows a commonly-used practice of multiplying the Bayes factors of individual events. The second method relies on an assumption that the mode phase can be determined from the inspiral waveform, so that coherent mode stacking of the data from different events becomes possible. Both methods significantly improve the chances of detecting the dominant post-merger signal, making a detection very likely after a year of observation with CE for certain EOS. We also show that in terms of detection, coherent stacking is more efficient in accumulating confidence. Moreover, assuming a 22 mode is detected with CE via stacking, we estimate through a Fisher analysis that the peak frequency can be measured to a statistical error of ~ 4-20 Hz for certain equations of state. Such an error corresponds to a NS radius measurement of ~ 15-56 m, a fractional relative error ~ 4 %, suggesting that systematic errors from theoretical modeling (~ 100 m) may dominate the error budget.

  • Pinning of longitudinal phonons in holographic spontaneous helices.- [PDF] - [Article] - [UPDATED]

    Tomas Andrade, Matteo Baggioli, Alexander Krikun, Napat Poovuttikul

    We consider the spontaneous breaking of translational symmetry and identify the associated Goldstone mode -- a longitudinal phonon -- in a holographic model with Bianchi VII helical symmetry. For the first time in holography, we observe the pinning of this mode after introducing a source for explicit breaking compatible with the helical symmetry of our setup. We study the dispersion relation of the resulting pseudo-Goldstone mode, uncovering how its speed and mass gap depend on the amplitude of the source and temperature. In addition, we extract the optical conductivity as a function of frequency, which reveals a metal-insulator transition as a consequence of the pinning.

  • Wormholes in $R^2$-gravity within the $f(R,T)$ formalism.- [PDF] - [Article] - [UPDATED]

    P.K. Sahoo, P.H.R.S. Moraes, Parbati Sahoo

    We propose, as a novelty in the literature, the modelling of wormholes within the particular case of the $f(R,T)$ gravity, namely $f(R,T)=R+\alpha R^{2}+\lambda T$, with $R$ and $T$ being the Ricci scalar and trace of the energy-momentum tensor, respectively, while $\alpha$ and $\lambda$ are constants. Although such a functional form application can be found in the literature, those concern to compact astrophysical objects, such that no wormhole analysis has been done so far. The quadratic geometric and linear material corrections of this theory make the matter content of the wormhole to remarkably be able to obey the energy conditions.

  • Can test fields destroy the event horizon in the Kerr-Taub-NUT spacetime?.- [PDF] - [Article] - [UPDATED]

    Koray Düztaş

    In this work we investigate if the interaction of the Kerr-Taub-NUT spacetime with test scalar and neutrino fields can lead to the destruction of the event horizon. It turns out that both extremal and nearly extremal black holes can be destroyed by scalar and neutrino fields if the initial angular momentum of the spacetime is sufficiently large relative to its mass and NUT charge. This is the first example in which a classical field satisfying the null energy condition can actually destroy an extremal black hole. For scalar fields, the modes that can lead to the destruction of the horizon are restricted to a narrow range due to superradiance. Since superradiance does not occur for neutrino fields, the destruction of the horizon by neutrino fields is generic, and it cannot be fixed by backreaction effects. We also show that the extremal black holes that can be destroyed by scalar fields correspond to naked singularities in the Kerr limit, in accord with the previous results which imply that extremal Kerr black holes cannot be destroyed by scalar test fields.

  • Branches of the Black Hole Wave Function Need Not Contain Firewalls.- [PDF] - [Article] - [UPDATED]

    Ning Bao, Sean M. Carroll, Aidan Chatwin-Davies, Jason Pollack, Grant N. Remmen

    We discuss the branching structure of the quantum-gravitational wave function that describes the evaporation of a black hole. A global wave function that initially describes a classical Schwarzschild geometry is continually decohered into distinct semiclassical branches by the emission of Hawking radiation. The laws of quantum mechanics dictate that the wave function evolves unitarily, but this unitary evolution is only manifest when considering the global description of the wave function: it is not implemented by time evolution on a single semiclassical branch. Conversely, geometric notions like the position or smoothness of a horizon only make sense on the level of individual branches. We consider the implications of this picture for probes of black holes by classical observers in definite geometries, like those involved in the AMPS construction. We argue that individual branches can describe semiclassical geometries free of firewalls, even as the global wave function evolves unitarily. We show that the pointer states of infalling detectors that are robust under Hamiltonian evolution are distinct from, and incompatible with, those of exterior detectors stationary with respect to the black hole horizon, in the sense that the pointer bases are related to each other via nontrivial transformations that mix system, apparatus, and environment. This result describes a Hilbert-space version of black hole complementarity.

  • Dark matter admixed strange quark stars in the Starobinsky model.- [PDF] - [Article] - [UPDATED]

    Ilidio Lopes, Grigoris Panotopoulos

    The properties of dark matter admixed strange quark stars are investigated in the Starobinsky model of modified gravity. For quark matter we assume the MIT bag model, while self-interacting dark matter inside the star is modelled as a Bose-Einstein condensate with a polytropic equation of state. We numerically integrate the structure equations in the Einstein frame adopting the two-fluid formalism treating the curvature correction term non-perturbatively. Our findings show that strange quark stars (in agreement with current observational constraints) with the highest masses are equally affected by dark matter and modified gravity.

  • Looking for light in the shadow.- [PDF] - [Article] - [CROSS LISTED]

    Slava G. Turyshev, Viktor T. Toth

    We study the electromagnetic (EM) field in the shadow cast by a large opaque sphere. For this, we consider the scattering of a high frequency monochromatic EM wave by the large sphere and develop a Mie theory that accounts for the presence of this obscuration. Applying fully absorbing boundary conditions, we find a solution for the Debye potentials, which we use to determine the EM field in the shadow in the wave zone at large distances from the sphere. We use the standard tools available from the nuclear scattering theory to develop the wave-optical treatment of the problem. Based on this treatment, we demonstrate that there is no EM field deep in the shadow, except for the field that is diffracted into the shadow by the edges of the sphere, as anticipated.


  • Exclusivity of p-N interactions within p-A collisions.- [PDF] - [Article]

    Thomas A. Trainor

    A geometric Glauber model applied to p-p or p-A collisions assumes that participant partons within a projectile nucleon independently follow eikonal trajectories, just as for projectile nucleons within target nuclei, and interact independently with any target nucleons encountered along their trajectory. A noneikonal quadratic relation for dijet production observed for p-p collisions suggests that such assumptions for p-N collisions may be incorrect. Data from p-A collisions supports that conclusion. For both isolated p-p collisions and for p-N interactions within p-A collisions a proton projectile interacts with only a single target nucleon within a brief time interval. Multiple overlapping p-N collisions are inhibited, suggesting the exclusivity of p-N interactions within p-A collisions.

  • Discovery potential of the NMSSM CP-odd Higgs at the LHC.- [PDF] - [Article]

    M. Almarashi

    In this paper we examine the LHC discovery potential of the lightest CP-odd Higgs boson, a1, of the NMSSM produced in gluon fusion channel gg->a1. We evaluate the inclusive signal rates of the a1 for a variety of decay channels and discuss its possible discovery. It is observed that the overall production and decay rates at inclusive level are quite sizable and should help extracting the a1 signal over some regions of the NMSSM parameter space.

  • Beautiful mathematics for beauty-full and other multi-heavy hadronic systems.- [PDF] - [Article]

    K. Azizi, A. R. Olamaei, S. Rostami

    In most non-perturbative methods in hadron physics the calculations are started with a correlation function in terms of some interpolating and transition currents in $ x $-space. For simplicity, the calculations are then transformed to the momentum space by a Fourier transformation.To suppress the contributions of the higher states and continuum; and enhance the ground state contribution, Borel transformation as well as continuum subtraction are applied by the help of quark-hadron duality assumption. In the present study we work out the mathematics required for these processes in the case of light and multi-heavy hadrons. We address a well-known problem in subtraction of the effects of the higher states and continuum and discuss how we find finite results without any divergence by using an appropriate representation of the modified Bessel functions, appearing in the heavy quark propagator, and successive applications of the Borel transformations, which lead to more suppression of the higher states and continuum contributions. The results obtained can be used in determination of the spectroscopic and decay properties of the multi-heavy standard and non-conventional (exotic) systems in many non-perturbative methods, specially the QCD sum rules.

  • NNLL resummation for the associated production of a top pair with a heavy boson at the LHC.- [PDF] - [Article]

    Alessandro Broggio

    In this presentation we review recent results on the resummation of soft gluon emission corrections for the associated production of a top-quark pair with a heavy boson (Higgs/W/Z) at the Large Hadron Collider (LHC). We develop a parton level Monte Carlo based on a soft-gluon resummation formula valid up to next-to-next-to-leading logarithmic (NNLL) accuracy. With this tool we study the impact of the newly computed corrections to the total cross sections and some important differential distributions.

  • Charm production in interactions of antiproton with proton and nuclei.- [PDF] - [Article]

    R. Shyam, K. Tsushima

    We study the production of charmed-baryons and charmed-mesons in the antiproton-proton and antiproton-nucleus interactions within a fully covariant model that is based on an effective Lagrangian approach. The charmed-baryon production proceeds via the $t$-channel $D^0$ and $D^{*0}$ meson-exchange diagrams, while the charmed-meson reactions are described as a sum of the $t$-channel $\Lambda_c^+$, $\Sigma_c^+$, $\Sigma_c^{++}$ baryon-exchange diagrams. We have also explored the production of charmed-baryon hypernucleus $^{16}_{\Lambda_c^+}$O in the antiproton - $^{16}$O collisions. For antiproton beam momenta of interest to the ${\bar P}ANDA$ experiment, the 0$^\circ$ differential cross sections for the formation of $^{16}_{\Lambda_c^+}$O hypernuclear states with simple particle-hole configurations, have magnitudes in the range of a few $\mu$b/sr.

  • The longitudinal leading-twist distribution amplitude of $J/\psi$ meson within background field theory.- [PDF] - [Article]

    Hai-Bing Fu, Long Zeng, Wei Cheng, Tao Zhong, Xing-Gang Wu

    We make a detailed study on the $J/\psi$ meson longitudinal leading-twist distribution amplitude $\phi_{2;J/\psi}^\|$ by using the QCD sum rules within the background field theory. By keeping all the non-perturbative condensates up to dimension-six, we obtain accurate QCD sum rules for the moments $\langle\xi_{n;J/\psi}^\|\rangle$. The first three ones are $\langle\xi_{2;J/\psi}^\|\rangle=0.083(12)$, $\langle\xi_{4;J/\psi}^\|\rangle=0.015(5)$ and $\langle\xi_{6;J/\psi}^\|\rangle=0.003(2)$, leading to a single peaked behavior for $\phi_{2;J/\psi}^\|$ which is sharper than the previous ones around the region of $x\sim0.5$. As an application, we adopt the QCD light-cone sum rules to calculate the $B_c$ meson semileptonic decay $B_c^+ \to J/\psi \ell^+ \nu_\ell$. We obtain $\Gamma(B_c^+ \to J/\psi \ell^+ \nu_\ell) = (89.67^{+24.76}_{-19.06}) \times 10^{-15}~{\rm GeV}$ and $\Re(J/\psi \ell^+ \nu_\ell) = 0.217^{+0.069}_{-0.057}$, which agree with the next-to-leading order pQCD prediction and the new CDF measurement within errors.

  • Information loss in effective field theory: entanglement and thermal entropies.- [PDF] - [Article]

    Daniel Boyanovsky

    Integrating out high energy degrees of freedom to yield a low energy effective field theory leads to a loss of information with a concomitant increase in entropy. We obtain the effective field theory of a light scalar field interacting with heavy fields after tracing out the heavy degrees of freedom from the time evolved density matrix. The initial density matrix describes the light field in its ground state and the heavy fields in equilibrium at a common temperature $T$. For $T=0$, we obtain the reduced density matrix in a perturbative expansion, it reveals an emergent mixed state as a consequence of the entanglement between light and heavy fields. We obtain the effective action that determines the time evolution of the \emph{reduced} density matrix for the light field in a non-perturbative Dyson resummation of one-loop correlations of the heavy fields. The Von-Neumann \emph{entanglement entropy} associated with the reduced density matrix is obtained for the non-resonant and resonant cases in the asymptotic long time limit. In the non-resonant case the reduced density matrix displays an \emph{incipient} thermalization albeit with a wave-vector, time and coupling dependent \emph{effective temperature} as a consequence of memory of initial conditions. The entanglement entropy is time independent and is the \emph{thermal entropy} for this effective, non-equilibrium temperature. In the resonant case the light field fully \emph{thermalizes} with the heavy fields, the reduced density matrix looses memory of the initial conditions and the entanglement entropy becomes the \emph{thermal entropy} of the light field. We discuss the relation between the entanglement entropy ultraviolet divergences and renormalization.

  • The next-to-leading order QCD and electroweak corrections to the Higgs-strahlung processes.- [PDF] - [Article]

    Pazilet Obul, Sayipjamal Dulat, Tie-Jun Hou, Ablikim Tursun, Nijat Yalkun

    In this paper we calculate the total and fiducial cross sections as well as differential distributions for the Higgs-strahlung or VH process $p p \to VH \to l\nu_l/l^- l^+ + H$, (V = W or Z ) including QCD and electro-weak corrections up to next-to-leading order by using the before and after reweighting photon PDFs of NNPDF2.3qed,NNPDF3.0qed, MRST2004qed, CT14QEDinc, and LUXqed at the LHC with 13 TeV and Higgs-boson mass $\ M_{H}=125$ GeV. The predictions from the various photon PDFs before and after reweighting against each other are in good agreement. The photon PDF uncertainties of the photon induced cross sections decrease significantly with the reweighting-PDFs.

  • Looking for the phase transition - recent NA61/SHINE results.- [PDF] - [Article]

    Ludwik Turko, NA61/SHINE Collaboration

    The fixed-target NA61/SHINE experiment (SPS CERN) looks for the critical point of strongly interacting matter and the properties of the onset of deconfinement. It is a two dimensional scan of measurements of particle spectra and fluctuations in proton-proton, proton-nucleus and nucleus-nucleus interactions as a function of collision energy and system size, corresponding to a two dimensional phase diagram (temperature T - baryonic chemical potential $\mu_B$). New NA61/SHINE results are presented here, such as transverse momentum and multiplicity fluctuations in Ar+Sc collisions compared to NA61/SHINE p+p and Be+Be data, as well as to earlier NA49 A+A results. Recently, a preliminary signature for the new size dependent effect - rapid changes in system size dependence was observed in NA61-SHINE data, labeled as percolation threshold or onset of fireball. This would be closely related to the vicinity of the hadronic phase transition region.

  • Chiral symmetry breaking and monopoles in gauge theories.- [PDF] - [Article]

    Adith Ramamurti, Edward Shuryak

    QCD monopoles are magnetically charged quasiparticles whose Bose-Einstein condensation (BEC) at $T<T_c$ creates electric confinement and flux tubes. The "magnetic scenario" of QCD proposes that scattering on the non-condensed component of the monopole ensemble at $T>T_c$ plays an important role in explaining the properties of strongly coupled quark-gluon plasma (sQGP) near the deconfinement temperature. In this paper, we study the phenomenon of chiral symmetry breaking and its relation to magnetic monopoles. Specifically, we study the eigenvalue spectrum of the Dirac operator in the basis of fermionic zero modes in an SU(2) monopole background. We find that as the temperature approaches the deconfinement temperature $T_c$ from above, the eigenvalue spectrum has a finite density at $\omega = 0$, indicating the presence of a chiral condensate. In addition, we find the critical scaling of the eigenvalue gap to be consistent with that of the correlation length in the 3d Ising model and the BEC transition of monopoles on the lattice.

  • Implications of new physics in the decays $B_c \to (J/\psi,\eta_c)\tau\nu$.- [PDF] - [Article]

    Chien-Thang Tran, Mikhail A. Ivanov, Jürgen G. Körner, Pietro Santorelli

    We study the semileptonic decays of the $B_c$ meson into final charmonium states within the standard model and beyond. The relevant hadronic transition form factors are calculated in the framework of the covariant confined quark model developed by us. We focus on the tau mode of these decays, which may provide some hints of new physics effects. We extend the standard model by assuming a general effective Hamiltonian describing the $b\to c\tau\nu$ transition, which consists of the full set of the four-fermion operators. We then obtain experimental constraints on the Wilson coefficients corresponding to each operator and provide predictions for the branching fractions and other polarization observables in different new physics scenarios.

  • Majorana neutrino and the vacuum of Bogoliubov quasiparticle.- [PDF] - [Article]

    Kazuo Fujikawa

    The Lagrangian of the seesaw mechanism is C violating but the same Lagrangian when re-written in terms of Majorana neutrinos is manifestly C invariant. To resolve this puzzling feature, a relativistic analogue of Bogoliubov transformation, which preserves CP but explicitly breaks C and P separately, was introduced together with the notions of a Bogoliubov quasiparticle and an analogue of the energy gap in BCS theory. The idea of Majorana neutrino as Bogoliubov quasiparticle was then suggested. In this paper, we study the vacuum structure of the Bogoliubov quasiparticle which becomes heavy by absorbing the C-breaking. By treating an infinitesimally small C violating term as an analogue of the chiral symmetry breaking nucleon mass in the model of Nambu and Jona-Lasinio, we construct an explicit form of the vacuum of the Bogoliubov quasiparticle which defines Majorana neutrinos in seesaw mechanism. The vacuum of the Bogoliubov quasiparticle thus constructed has an analogous condensate structure as the vacuum of the quasiparticle (nucleon) in the Nambu--Jona-Lasinio model.

  • Degenerate Vacua of the Universe and What Comes Beyond the Standard Model.- [PDF] - [Article]

    B.G. Sidharth, C.R. Das, C.D. Froggatt, H.B. Nielsen, Larisa Laperashvili

    We present a new cosmological model of the Universe based on the two discoveries: 1. cosmological constant is very small, and 2. Nature shows a new law in physics called "Multiple Point Principle" (MPP). The MPP predicts the two degenerate vacua of the Universe with VEV $v_1\approx 246$ Gev and $v_2\sim 10^{18}$ GeV, which provide masses of the Higgs boson and top-quark. A new cosmological model assumes the formation of two universal bubbles. The Universe at first stage of its existing is a bubble with a de-Sitter spacetime inside, having black-holes-hedgehogs as topological defects of the vacuum. Such a bubble has a "false vacuum" with VEV $v_2$, which decays very quickly. Cooling Universe has a new phase transition, transforming the "false" vacuum to the "true" (Electroweak) vacuum. Hedgehogs confined, and the universal bubble is transformed into the bubble having spacetime with FLRW-metric and the vacuum with new topological defects of $U(1)_{(el-mag)}$ group: magnetic vortices and Sidharth's pointlike defects. The problem of stability/metastability of the EW-vacuum is investigated. Noncommutativity of the vacua spacetime manifold is discussed. The prediction of a new physics is given by the future observations at LHC of the triplet $SU(2)$ Higgs bosons (at energies $E\sim 10$ TeV), and/or of the new bound states $6t + 6\bar t$ formed by top-antitop quarks (at $E\sim 1$ TeV). The problem "What comes beyond the Standard Model" is discussed at the end of this paper.

  • Comment on high-$p_T$ inclusive spectra measurements at the LHC.- [PDF] - [Article]

    S.M. Troshin, N.E. Tyurin

    The high-$p_T$ inclusive spectra measured at the LHC demonstrate a non-perturbative $p_T^{-6}$ dependence. This can be related to observation of a nondecreasing with $p_T$ one-spin asymmetries at RHIC questioning the fact of the spin degrees of freedom neglect at the LHC energies.

  • Black disk, maximal Odderon and unitarity.- [PDF] - [Article]

    V.A. Khoze, A.D. Martin, M.G. Ryskin

    We argue that the so-called maximal Odderon contribution breaks the `black disk' behaviour of the asymptotic amplitude, since the cross section of the events with Large Rapidity Gaps grows faster than the total cross section. That is the `maximal Odderon' is not consistent with the unitarity.

  • Disclosing $D^*\bar{D}^*$ molecular states in the $B_c^- \to \pi^- J/\psi \omega$ decay.- [PDF] - [Article]

    L.R.Dai, J.M.Dias, E.Oset

    We study the $B_c^- \to \pi^- J/\psi \omega$ and $B_c^- \to \pi^- D^* \bar{D}^*$ reactions and show that they are related by the presence of two resonances, the $X(3940)$ and $X(3930)$, that are of molecular nature and couple most strongly to $D^* \bar{D}^*$, but also to $J/\psi\omega$. Because of that, in the $J/\psi\omega$ mass distribution we find a cusp with large strength at the $D^* \bar{D}^*$ threshold and predict the ratio of strengths between the peak of the cusp and the maximum of the $D^* \bar{D}^*$ distribution close to $D^* \bar{D}^*$ threshold, which are distinct features of the molecular nature of these two resonances.

  • Testing Spin-2 Mediator in $b\rightarrow s \mu^+ \mu^-$.- [PDF] - [Article]

    Svjetlana Fajfer, Blazenka Melic, Monalisa Patra

    We consider effects of spin-2 particle in the $b\rightarrow s \mu^+ \mu^-$ transition in a model independent way. Our assumptions are that the spin-2 particle has flavour non-universal coupling with $b$ and $s$ quarks and that it couples to muons only. The $B_s - \bar B_s$ transition gives the strong constraint on the coupling of the spin-2 mediator and $b$ and $s$ quarks. The observed discrepancy from the SM prediction for the muon anomalous magnetic moment $ (g-2)_\mu$ serves us to constrain the $\mu$-coupling to spin-2 particle. We find that the spin-2 particle can generate the forward-backward asymmetry in $B \to K \mu^+ \mu^-$ which is not present in the Standard Model and results in a considerable deviation from the SM value in case of $B \to K^* \mu^+ \mu^-$ decays. In both decay modes the forward-backward asymmetry can reach almost $15\%$. Other observables for these decays receive tiny effects.

  • Charged Lepton Flavor Violation in a class of Radiative Neutrino Mass Generation Models.- [PDF] - [Article]

    Talal Ahmed Chowdhury, Salah Nasri

    We investigate charged lepton flavor violating processes $\mu\rightarrow e \gamma$, $\mu\rightarrow e e \overline{e}$ and $\mu-e$ conversion in nuclei for a class of three-loop radiative neutrino mass generation models with electroweak multiplets of increasing order. We find that, because of certain cancellations among various one-loop diagrams which give the dipole and non-dipole contributions in effective $\mu e \gamma$ vertex and Z-penguin contribution in effective $\mu e Z$ vertex, the flavor violating processes $\mu\rightarrow e\gamma$ and $\mu-e$ conversion in nuclei become highly suppressed compared to $\mu\rightarrow e e \overline{e}$ process. Therefore, the observation of such pattern in LFV processes may reveal the radiative mechanism behind neutrino mass generation.

  • Calculation of the hadronic vacuum polarization contribution to the muon anomalous magnetic moment.- [PDF] - [Article]

    T. Blum, P.A. Boyle, V. Gülpers, T. Izubuchi, L. Jin, C. Jung, A. Jüttner, C. Lehner, A. Portelli, J.T. Tsang

    We present a first-principles lattice QCD+QED calculation at physical pion mass of the leading-order hadronic vacuum polarization contribution to the muon anomalous magnetic moment. The total contribution of up, down, strange, and charm quarks including QED and strong isospin breaking effects is found to be $a_\mu^{\rm HVP~LO}=715.4(16.3)(9.2) \times 10^{-10}$, where the first error is statistical and the second is systematic. By supplementing lattice data for very short and long distances with experimental R-ratio data using the compilation of Ref. [1], we significantly improve the precision of our calculation and find $a_\mu^{\rm HVP~LO} = 692.5(1.4)(0.5)(0.7)(2.1) \times 10^{-10}$ with lattice statistical, lattice systematic, R-ratio statistical, and R-ratio systematic errors given separately. This is the currently most precise determination of the leading-order hadronic vacuum polarization contribution to the muon anomalous magnetic moment. In addition, we present the first lattice calculation of the light-quark QED correction at physical pion mass.

  • The complete HEFT Lagrangian after the LHC Run I.- [PDF] - [Article] - [UPDATED]

    I. Brivio, J. Gonzalez-Fraile, M. C. Gonzalez-Garcia, L. Merlo

    The complete effective chiral Lagrangian for a dynamical Higgs is presented and constrained by means of a global analysis including electroweak precision data together with Higgs and triple gauge boson coupling data from the LHC Run~I. The operators' basis up to next-to-leading order in the expansion consists of 148 (188 considering right-handed neutrinos) flavour universal terms and it is presented here making explicit the custodial nature of the operators. This effective Lagrangian provides the most general description of the physical Higgs couplings once the electroweak symmetry is assumed, and it allows for deviations from the $SU(2)_L$ doublet nature of the Standard Model Higgs. The comparison with the effective linear Lagrangian constructed with an exact $SU(2)_L$ doublet Higgs and considering operators with at most canonical dimension six is presented. A promising strategy to disentangle the two descriptions consists in analysing i) anomalous signals present only in the chiral Lagrangian and not expected in the linear one, that are potentially relevant for LHC searches, and ii) decorrelation effects between observables that are predicted to be correlated in the linear case and not in the chiral one. The global analysis presented here, that includes several kinematic distributions, is crucial for reducing the allowed parameter space and for controlling the correlations between parameters. This improves previous studies aimed at investigating the Higgs Nature and the origin of the electroweak symmetry breaking.

  • Alien calculus and a Schwinger--Dyson equation: two-point function with a nonperturbative mass scale.- [PDF] - [Article] - [UPDATED]

    Marc P. Bellon, Pierre J. Clavier

    Starting from the Schwinger--Dyson equation and the renormalization group equation for the massless Wess--Zumino model, we compute the dominant nonperturbative contributions to the anomalous dimension of the theory, which are related by alien calculus to singularities of the Borel transform on integer points. The sum of these dominant contributions has an analytic expression. When applied to the two-point function, this analysis gives a tame evolution in the deep euclidean domain at this approximation level, making doubtful the arguments on the triviality of the quantum field theory with positive \(\beta\)-function. On the other side, we have a singularity of the propagator for time like momenta of the order of the renormalization group invariant scale of the theory, which has a nonperturbative relationship with the renormalization point of the theory. All these results do not seem to have an interpretation in terms of semiclassical analysis of a Feynman path integral.

  • Regularization with Numerical Extrapolation for Finite and UV-Divergent Multi-loop Integrals.- [PDF] - [Article] - [UPDATED] Doncker, F.Yuasa, K.Kato, T.Ishikawa, J.Kapenga, O.Olagbemi

    We give numerical integration results for Feynman loop diagrams such as those covered by Laporta [1] and by Baikov and Chetyrkin [2], and which may give rise to loop integrals with UV singularities. We explore automatic adaptive integration using multivariate techniques from the PARINT package for multivariate integration, as well as iterated in- tegration with programs from the QUADPACK package, and a trapezoidal method based on a double exponential trans- formation. PARINT is layered over MPI (Message Passing Interface), and incorporates advanced parallel/distributed techniques including load balancing among processes that may be distributed over a cluster or a network/grid of nodes. Results are included for 2-loop vertex and box diagrams and for sets of 2-, 3- and 4-loop self-energy diagrams with or without UV terms. Numerical regularization of integrals with singular terms is achieved by linear and non-linear extrapolation methods.

  • The Minimal GUT with Inflaton and Dark Matter Unification.- [PDF] - [Article] - [UPDATED]

    Heng-Yu Chen, Ilia Gogoladze, Shan Hu, Tianjun Li, Lina Wu

    Giving up the solutions to the fine-tuning problems, we propose the non-supersymmetric flipped $SU(5)\times U(1)_X$ model based on the minimal particle content principle, which can be constructed from the four-dimensional $SO(10)$ models, five-dimensional orbifold $SO(10)$ models, and local F-theory $SO(10)$ models. To achieve gauge coupling unification, we introduce one pair of vector-like fermions, which form complete $SU(5)\times U(1)_X$ representation. Proton lifetime is around $5\times 10^{35}$ years, neutrino masses and mixing can be explained via seesaw mechanism, baryon asymmetry can be generated via leptogenesis, and vacuum stability problem can be solved as well. In particular, we propose that inflaton and dark matter particle can be unified to a real scalar field with $Z_2$ symmetry, which is not an axion and does not have the non-minimal coupling to gravity. Such kind of scenarios can be applied to the generic scalar dark matter models. Also, we find that the vector-like particle corrections to the $B_s^0$ masses can be about 6.6%, while their corrections to the $K^0$ and $B_d^0$ masses are negligible.

  • Stop Co-Annihilation in the Minimal Supersymmetric Standard Model Revisited.- [PDF] - [Article] - [UPDATED]

    Aaron Pierce, Nausheen R. Shah, Stefan Vogl

    We re-examine the stop co-annihilation scenario of the Minimal Supersymmetric Standard Model, wherein a bino-like lightest supersymmetric particle has a thermal relic density set by co-annihilations with a scalar partner of the top quark in the early universe. We concentrate on the case where only the top partner sector is relevant for the cosmology, and other particles are heavy. We discuss the cosmology with focus on low energy parameters and an emphasis on the implications of the measured Higgs boson mass and its properties. We find that the irreducible direct detection signal correlated with this cosmology is generically well below projected experimental sensitivity, and in most cases lies below the neutrino background. A larger, detectable, direct detection rate is possible, but is unrelated to the co-annihilation cosmology. LHC searches for compressed spectra are crucial for probing this scenario.

  • Heavy stable charged tracks as signatures of non-thermal dark matter at the LHC : a study in some non-supersymmetric scenarios.- [PDF] - [Article] - [UPDATED]

    Avirup Ghosh, Tanmoy Mondal, Biswarup Mukhopadhyaya

    We consider two theoretical scenarios, each including a $\mathbb{Z}_{2}$-odd sector and leading to an elementary dark matter candidate. The first one is a variant of the Type-III seesaw model where one lepton triplet is $\mathbb{Z}_{2}$-odd, together with a heavy sterile neutrino. It leads to a fermionic dark matter, together with the charged component of the triplet being a quasi-stable particle which decays only via a higher-dimensional operator suppressed by a high scale. The second model consists of an inert scalar doublet together with a $\mathbb{Z}_{2}$-odd right-handed Majorana neutrino dark matter. A tiny Yukawa coupling delays the decay of the charged component of the inert doublet into the dark matter candidate, making the former long-lived on the scale of collider detectors. The parameter space of each model has been constrained by big-bang nucleosynthesis constraints, and also by estimating the contribution to the relic density through freeze-out of the long-lived charged particle as well the freeze-in production of the dark matter candidate. We consider two kinds of signals at the Large Hadron Collider for the first kind of models, namely two charged tracks and single track + MET. For the second kind, the characteristic signals are opposite as well as same-sign charged track pairs. We perform a detailed analysis using event selection criteria consistent with the current experimental programmes. It is found that the scenario with a lepton triplet can be probed upto 960(1190) GeV with an integrated luminosity of 300(3000) $fb^{-1}$, while the corresponding numbers for the inert doublet scenario are 630(800) GeV. Furthermore, the second kind of signal mentioned in each case allows us to differentiate different dark matter scenarios from each other.

  • Correlating Lepton Flavour (Universality) Violation in $B$ Decays with $\mu\to e\gamma$ using Leptoquarks.- [PDF] - [Article] - [UPDATED]

    Andreas Crivellin, Dario Mueller, Adrian Signer, Yannick Ulrich

    Motivated by the measurements of $b\to s\ell^+\ell^-$ transitions, including $R(K)$ and $R(K^*)$, we examine lepton flavour (universality) violation in $B$ decays and its connections to $\mu\to e\gamma$ in generic leptoquark models. Considering all 10 representations of scalar and vector leptoquarks under the Standard Model gauge group we compute the tree-level matching for semileptonic $b$-quark operators as well as their loop effects in $\ell\to\ell^\prime\gamma$. In our phenomenological analysis we correlate $R(K)$, $R(K^*)$ and the other $b\to s\mu^+\mu^-$ data to $\mu\to e\gamma$ and $b\to s\mu e$ transitions for the three leptoquark representations that generate left-handed currents in $b\to s\ell^+\ell^-$ transitions and, therefore, provide a good fit to data. We find that while new physics contributions to muons are required by the global fit, also couplings to electrons can be sizeable without violating the stringent bounds from $\mu\to e\gamma$. In fact, if the effect in electrons in $b\to s\ell^+\ell^-$ has opposite sign than the effect in muons the bound from $\mu\to e\gamma$ can always be avoided. However, unavoidable effects in $b\to s\mu e$ transitions (i.e. $B_s\to\mu e$, $B\to K\mu e$, etc.) appear which are within the reach of LHCb and BELLE II.

  • Lepton flavor changing Higgs Boson decays in a Two Higgs Doublet Model with a fourth generation of fermions.- [PDF] - [Article] - [UPDATED]

    S. Chamorro-Solano, A. Moyotl, M. A. Pérez

    We analyze the flavor changing decay $h\rightarrow \mu \tau $ in the framework of a Two Higgs Doublet Model with a fourth generation of fermions (4G2HDM) which couples only to the heavy scalar doublet. We obtain that the respective branching ratio at one-loop level can reach values as high as $ 10^{-6} $ for a mass of $ 100-350 $ GeV of the heavy lepton in the fourth family and a heavy Higgs boson with mass in the range $ 200-700 $ GeV. These radiative corrections are of the same order of magnitude as the tree level prediction of the 4G2HDM.

  • Minimal realization of right-handed gauge symmetry.- [PDF] - [Article] - [UPDATED]

    Takaaki Nomura, Hiroshi Okada

    We propose a minimally extended gauge symmetry model with $U(1)_R$, where only the right-handed fermions have nonzero charges in the fermion sector. To achieve both anomaly cancellations and minimality, three right-handed neutrinos are naturally required, and the standard model Higgs has to have nonzero charge under this symmetry. Then we find that its breaking scale($\Lambda$) is restricted by precise measurement of neutral gauge boson in the standard model; therefore, ${\cal O}$(10) TeV$\lesssim \Lambda$. We also discuss its testability of the new gauge boson and discrimination of $U(1)_R$ model from $U(1)_{B-L}$ one at collider physics such as LHC and ILC.

  • Nonperturbative renormalization of nonlocal quark bilinears for quasi-PDFs on the lattice using an auxiliary field.- [PDF] - [Article] - [UPDATED]

    Jeremy Green, Karl Jansen, Fernanda Steffens

    Quasi-PDFs provide a path toward an ab initio calculation of parton distribution functions (PDFs) using lattice QCD. One of the problems faced in calculations of quasi-PDFs is the renormalization of a nonlocal operator. By introducing an auxiliary field, we can replace the nonlocal operator with a pair of local operators in an extended theory. On the lattice, this is closely related to the static quark theory. In this approach, we show how to understand the pattern of mixing that is allowed by chiral symmetry breaking, and obtain a master formula for renormalizing the nonlocal operator that depends on three parameters. We present an approach for nonperturbatively determining these parameters and use perturbation theory to convert to the MS-bar scheme. Renormalization parameters are obtained for two lattice spacings using Wilson twisted mass fermions and for different discretizations of the Wilson line in the nonlocal operator. Using these parameters we show the effect of renormalization on nucleon matrix elements with pion mass approximately 370 MeV, and compare renormalized results for the two lattice spacings. The renormalized matrix elements are consistent among the different Wilson line discretizations and lattice spacings.

  • The Born-Oppenheimer approximation in an effective field theory language.- [PDF] - [Article] - [UPDATED]

    Nora Brambilla, Gastão Krein, Jaume Tarrús Castellà, Antonio Vairo

    The Born--Oppenheimer approximation is the standard tool for the study of molecular systems. It is founded on the observation that the energy scale of the electron dynamics in a molecule is larger than that of the nuclei. A very similar physical picture can be used to describe QCD states containing heavy quarks as well as light-quarks or gluonic excitations. In this work, we derive the Born--Oppenheimer approximation for QED molecular systems in an effective field theory framework by sequentially integrating out degrees of freedom living at energies above the typical energy scale where the dynamics of the heavy degrees of freedom occurs. In particular, we compute the matching coefficients of the effective field theory for the case of the $H^+_2$ diatomic molecule that are relevant to compute its spectrum up to ${\cal O}(m\alpha^5)$. Ultrasoft photon loops contribute at this order, being ultimately responsible for the molecular Lamb shift. In the effective field theory the scaling of all the operators is homogeneous, which facilitates the determination of all the relevant contributions, an observation that may become useful for high-precision calculations. Using the above case as a guidance, we construct under some conditions an effective field theory for QCD states formed by a color-octet heavy quark-antiquark pair bound with a color-octet light-quark pair or excited gluonic state, highlighting the similarities and differences between the QED and QCD systems. Assuming that the multipole expansion is applicable, we construct the heavy-quark potential up to next-to-leading order in the multipole expansion in terms of nonperturbative matching coefficients to be obtained from lattice QCD.

  • Relating centrality to impact parameter in nucleus-nucleus collisions.- [PDF] - [Article] - [UPDATED]

    Sruthy Jyothi Das, Giuliano Giacalone, Pierre-Amaury Monard, Jean-Yves Ollitrault

    In ultrarelativistic heavy-ion experiments, one estimates the centrality of a collision by using a single observable, say $n$, typically given by the transverse energy or the number of tracks observed in a dedicated detector. The correlation between $n$ and the impact parameter, $b$, of the collision is then inferred by fitting a specific model of the collision dynamics, such as the Glauber model, to experimental data. The goal of this paper is to assess precisely which information about $b$ can be extracted from data without any specific model of the collision. Under the sole assumption that the probability distribution of $n$ for a fixed $b$ is Gaussian, we show that the probability distribution of the impact parameter in a narrow centrality bin can be accurately reconstructed up to $5\%$ centrality. We apply our methodology to data from the Relativistic Heavy Ion Collider and the Large Hadron Collider. We propose a simple measure of the precision of the centrality determination, which can be used to compare different experiments.

  • Production of $HHH$ and $HHV(V=\gamma,Z)$ at the hadron colliders.- [PDF] - [Article] - [UPDATED]

    Pankaj Agrawal, Debashis Saha, Ambresh Shivaji

    We consider the production of two Higgs bosons in association with a gauge boson or another Higgs boson at the hadron colliders. We compute the cross sections and distributions for the processes $ p p \to H H H $ and $H H Z$ within the standard model. In particular, we compute the gluon-gluon fusion one-loop contributions mediated via heavy quarks in the loop. It is the leading order contribution to $ p p \to H H H $ process. To the process $ p p \to H H Z $, it is next-to-next-to-leading-order (NNLO) contribution in QCD coupling. We also compare this contribution to the next-to-leading-order (NLO) QCD contribution to this process. The NNLO contribution can be similar to NLO contribution at the Large Hadron Collider (LHC), and significantly more at higher center-of-mass energy machines. We also study new physics effects in these processes by considering $ttH, HHH, HHHH, HZZ$, and $HHZZ$ interactions as anomalous. The anomalous couplings can enhance the cross sections significantly. The $gg \to HHH$ process is specially sensitive to anomalous trilinear Higgs boson self-coupling. For the $gg \to HHZ$ process, there is some modest dependence on anomalous $HZZ$ couplings.

  • Energy density and path-length dependence of the fractional momentum loss in heavy-ion collisions at $\sqrt{s_{\rm NN}}$ from 62.4 to 5020 GeV.- [PDF] - [Article] - [UPDATED]

    Antonio Ortiz, Omar Vázquez

    In this work a study of the fractional momentum loss ($S_{\rm loss}$) as a function of the characteristic path-length ($L$) and the Bjorken energy density times the equilibration time ($\epsilon_{\rm Bj}\tau_{0}$) for heavy-ion collisions at different $\sqrt{s_{\rm NN}}$ is presented. The study has been conducted using inclusive charged particles from intermediate to large transverse momentum ($5<p_{\rm T}<20$ GeV/$c$). Within uncertainties and for all the transverse momentum values which were explored, the fractional momentum loss linearly increases with $({\epsilon_{\rm Bj}\tau_{0}})^{3/8}$$L$. The functional form of $S_{\rm loss}$ vs. $({\epsilon_{\rm Bj}\tau_{0}})^{3/8}$$L$ seems to be universal. Moreover, for identified charged hadrons a linear relationship between $S_{\rm loss}$ and $L$ is also observed. The behaviour of data could provide important information aimed to understand the parton energy loss mechanism in heavy-ion collisions and some insight into the expected effect for small systems.

  • Explaining Dark Matter and Neutrino Mass in the light of TYPE-II Seesaw Model.- [PDF] - [Article] - [UPDATED]

    Anirban Biswas, Avirup Shaw

    With the motivation of simultaneously explaining dark matter and neutrino masses, mixing angles, we have invoked the Type-II seesaw model extended by an extra $SU(2)$ doublet $\Phi$. Moreover, we have imposed a $\mathbb{Z}_2$ parity on $\Phi$ which remains unbroken as the vacuum expectation value of $\Phi$ is zero. Consequently, the lightest neutral component of $\Phi$ becomes naturally stable and can be a viable dark matter candidate. On the other hand, light Majorana masses for neutrinos have been generated following usual Type-II seesaw mechanism. Further in this framework, for the first time, we have derived the full set of vacuum stability and unitarity conditions, which must be satisfied to obtain a stable vacuum as well as to preserve the unitarity of the model respectively. Thereafter, we have performed extensive phenomenological studies of both dark matter and neutrino sectors considering all possible theoretical and current experimental constraints. Finally, we have also discussed a qualitative collider signatures of dark matter and associated odd particles at the 13 TeV Large Hadron Collider.

  • $Z$-boson decays to a vector quarkonium plus a photon.- [PDF] - [Article] - [UPDATED]

    Geoffrey T. Bodwin, Hee Sok Chung, June-Haak Ee, Jungil Lee

    We compute the decay rates for the processes $Z\to V+\gamma$, where $Z$ is the $Z$ boson, $\gamma$ is the photon, and $V$ is one of the vector quarkonia $J/\psi$ or $\Upsilon(nS)$, with $n=1$, $2$, or $3$. Our computations include corrections through relative orders $\alpha_s$ and $v^2$ and resummations of logarithms of $m_Z^2/m_Q^2$, to all orders in $\alpha_s$, at NLL accuracy. ($v$ is the velocity of the heavy quark $Q$ or the heavy antiquark $\bar{Q}$ in the quarkonium rest frame, and $m_Z$ and $m_Q$ are the masses of $Z$ and $Q$, respectively.) Our calculations are the first to include both the order-$\alpha_s$ correction to the light-cone distributions amplitude and the resummation of logarithms of $m_Z^2/m_Q^2$ and are the first calculations for the $\Upsilon(2S)$ and $\Upsilon(3S)$ final states. The resummations of logarithms of $m_Z^2/m_Q^2$ that are associated with the order-$\alpha_s$ and order-$v^2$ corrections are carried out by making use of the Abel-Pad\'e method. We confirm the analytic result for the order-$v^2$ correction that was presented in a previous publication, and we correct the relative sign of the direct and indirect amplitudes and some choices of scales in that publication. Our branching fractions for $Z\to J/\psi+\gamma$ and $Z\to \Upsilon(1S)+\gamma$ differ by $2.0\,\sigma$ and $-4.0\,\sigma$, respectively, from the branching fractions that are given in the most recent publication on this topic (in units of the uncertainties that are given in that publication). However, we argue that the uncertainties in the rates are underestimated in that publication.

  • Did TOTEM experiment discover the Odderon?.- [PDF] - [Article] - [UPDATED]

    Evgenij Martynov, Basarab Nicolescu

    The present study shows that the new TOTEM datum $\rho^{pp} = 0.098 \pm 0.01$ can be considered as the first experimental discovery of the Odderon, namely in its maximal form.

  • Low-Energy Effective Field Theory below the Electroweak Scale: Anomalous Dimensions.- [PDF] - [Article] - [UPDATED]

    Elizabeth E. Jenkins, Aneesh V. Manohar, Peter Stoffer

    We compute the one-loop anomalous dimensions of the low-energy effective Lagrangian below the electroweak scale, up to terms of dimension six. The theory has 70 dimension-five and 3631 dimension-six Hermitian operators that preserve baryon and lepton number, as well as additional operators that violate baryon number and lepton number. The renormalization group equations for the quark and lepton masses and the QCD and QED gauge couplings are modified by dimension-five and dimension-six operator contributions. We compute the renormalization group equations from one insertion of dimension-five and dimension-six operators, as well as two insertions of dimension-five operators, to all terms of dimension less than or equal to six. The use of the equations of motion to eliminate operators can be ambiguous, and we show how to resolve this ambiguity by a careful use of field redefinitions.

  • MagnetoHydrodynamics with chiral anomaly: phases of collective excitations and instabilities.- [PDF] - [Article] - [UPDATED]

    Koichi Hattori, Yuji Hirono, Ho-Ung Yee, Yi Yin

    We study the relativistic hydrodynamics with chiral anomaly and dynamical electromagnetic fields, namely Chiral MagnetoHydroDynamics (CMHD). We formulate the CMHD as a low-energy effective theory based on a derivative expansion. We demonstrate the modification of ordinary MagnetoHydroDynamics (MHD) due to chiral anomaly can be obtained from the second law of thermodynamics and is tied to chiral magnetic effect with the universal coefficient. When axial charge imbalance becomes larger than a critical value, a new type of collective gapless excitation in the CMHD appears, as a result of the interplay among magnetic field, flow velocity, and chiral anomaly; we call it "Chiral MagnetoHelical Mode" (CMHM). These modes carry definite magnetic and fluid helicities and will either grow exponentially or dissipate in time, depending on the relative sign between their helicity and axial charge density. The presence of exponentially growing CMHM indicates a hydrodynamic instability.

  • Baryon Chiral Perturbation Theory combined with the ${\mathbf{1/N_c}}$ Expansion in SU(3) I: Framework.- [PDF] - [Article] - [UPDATED]

    Ishara P. Fernando, Jose L. Goity

    Baryon Chiral Perturbation Theory combined with the $1/N_c$ expansion is implemented for three flavors. Baryon masses, vector charges and axial vector couplings are studied to one-loop and organized according to the $\xi$-expansion, in which the $1/N_c$ and the low energy power countings are linked according to $1/N_c={\cal{O}}(\xi)={\cal{O}}(p)$. The renormalization to ${\cal{O}}(\xi^3)$ necessary for the mentioned observables is provided, along with applications to the baryon masses and axial couplings as obtained in lattice QCD calculations.

  • Once More on Coulomb-Nuclear Interference.- [PDF] - [Article] - [UPDATED]

    Vladimir A. Petrov

    This is a critical reconsideration of the standard way of account for Coulomb-nuclear interference in elastic scattering amplitude.

  • Tachyon constant-roll inflation.- [PDF] - [Article] - [UPDATED]

    A. Mohammadi, Kh. Saaidi, T. Golanbari

    The constant-roll inflation is studied where the inflaton is taken as a tachyon field. Since in this approach the second slow-roll parameter is assumed to be of order one instead of being small, then the perturbation parameters will be considered again. The results are compared with observational data, and it is confirmed that the model could stand as a proper candidate for inflation.

  • Hall effect in the presence of rotation.- [PDF] - [Article] - [UPDATED]


    The rotating relativistic fermion system is considered. The consideration is based on the Dirac equation written in the laboratory (non - rotating) reference frame. Rotation in this approach gives rise to the effective magnetic and electric fields that act in the same way both on positive and negative electric charges. In the presence of external electric field in the given system the electric current appears orthogonal to both the electric field and the axis of rotation. The possible applications to the physics of quark - gluon plasma are discussed.


  • Scaling dimensions of Coulomb branch operators of 4d N=2 superconformal field theories.- [PDF] - [Article]

    Philip C. Argyres, Mario Martone

    Under reasonable assumptions about the complex structure of the set of singularities on the Coulomb branch of $\mathcal N=2$ superconformal field theories, we present a relatively simple and elementary argument showing that the scaling dimension, $\Delta$, of a Coulomb branch operator of a rank $r$ theory is allowed to take values in a finite set of rational numbers$\Delta\in \big[\frac{n}{m}\big|n,m\in\mathbb N, 0<m\le n, gcd(n,m)=1,\ \varphi(n)\le2r\big]$ where $\varphi(n)$ is the Euler totient function. The maximal dimension grows superlinearly with rank as $\Delta_\text{max} \sim r \ln\ln r$. This agrees with the recent result of Caorsi and Cecotti.

  • Phase transition for the system of small volume in the $\phi^4$ theory in the Tsallis nonextensive statistics.- [PDF] - [Article]

    Masamichi Ishihara

    We studied the effects of the nonextensivity on the phase transition for the system of small volume $V$ in the $\phi^4$ theory in the Tsallis nonextensive statistics of entropic parameter $q$ and temperature $T$, when the deviation from the Boltzmann-Gibbs statistics, $|q-1|$, is small. We calculated the condensate and the mass to the order $q-1$ with the normalized $q$-expectation value under the massless free particle approximation. The following facts were found. The condensate $\Phi$ divided by $v$, $\Phi/v$, at $q$ is smaller than that at $q'$ for $q>q'$ as a function of $T_{\mathrm{ph}}/v$ which is the physical temperature $T_{\mathrm{ph}}$ divided by $v$, where $T_{\mathrm{ph}}$ at $q=1$ coincides with $T$ and $v$ is the value of the condensate at $T=0$. The mass decreases, reaches minimum, and increases after that, as $T_{\mathrm{ph}}$ increases. The mass at $q>1$ is lighter than the mass at $q=1$ at low physical temperature and heavier than the mass at $q=1$ at high physical temperature. The effects of the nonentensivity on the physical quantity as a function of $T_{\mathrm{ph}}$ become strong as $|q-1|$ increases. The results indicate the significance of the definition of the expectation value, the definition of the physical temperature, and the constraints for the density operator, when the terms including the volume of the system are not negligible.

  • N=4 Super-Schwarzian Theory on the Coadoint Orbit and PSU(1,1|2).- [PDF] - [Article]

    Shogo Aoyama, Yuco Honda

    An N=4 super-Schwarzian theory is formulated by the coadjoint orbit method. It is discovered that the action has a hidden symmetry under PSU(1,1|2).

  • $R^4 $ terms in supergravities via T-duality constraint.- [PDF] - [Article]

    Hamid Razaghian, Mohammad R. Garousi

    It has been speculated in the literature that the effective actions of string theories at any order of $\alpha'$ should be invariant under the Buscher rules plus their higher covariant derivative corrections. This may be used as a constraint to find effective actions at any order of $\alpha'$, in particular, the metric, the B-field and the dilaton couplings in supergravities at order $\alpha'^3$ up to an overall factor. For the simple case of zero B-field and diagonal metric in which we have done the calculations explicitly, we have found that the constraint fixes almost all the seven independent Riemann curvature couplings. There is only one term which is not fixed, because when metric is diagonal, the reduction of two $R^4$ terms become identical. The Riemann curvature couplings that the T-duality constraint produces for both type II and Heterotic theories are fully consistent with the existing couplings in the literature which have been found by the S-matrix and by the sigma-model approaches.

  • Casimir squared correction to the standard rotator Hamiltonian for the O($n$) sigma-model in the delta-regime.- [PDF] - [Article]

    Ferenc Niedermayer, Peter Weisz

    In a previous paper we found that the isospin susceptibility of the O($n$) sigma-model calculated in the standard rotator approximation differs from the next-to-next to leading order chiral perturbation theory result in terms vanishing like $1/\ell\,,$ for $\ell=L_t/L\to\infty$ and further showed that this deviation could be described by a correction to the rotator spectrum proportional to the square of the quadratic Casimir invariant. Here we confront this expectation with analytic nonperturbative results on the spectrum in 2 dimensions, by Balog and Heged\"us for $n=3,4$ and by Gromov, Kazakov and Vieira for $n=4$. We also consider the case of 3 dimensions.

  • On large $q$ expansion in the Sachdev-Ye-Kitaev model.- [PDF] - [Article]

    Grigory Tarnopolsky

    We consider the Sachdev-Ye-Kitaev (SYK) model where interaction involves $q$ fermions at a time. We find the next order correction to the thermal two-point function in the large $q$ expansion. Using this result we find the next order correction to the SYK free energy.

  • The $T\overline T$ deformation of quantum field theory as a stochastic process.- [PDF] - [Article]

    John Cardy

    We revisit the results of Zamolodchikov and others on the deformation of two-dimensional quantum field theory by the determinant $\det T$ of the stress tensor, commonly referred to as $T\overline T$. Infinitesimally this is equivalent to a random coordinate transformation, with a local action which is, however, a total derivative and therefore gives a contribution only from boundaries or nontrivial topology. We discuss in detail the examples of a torus, a finite cylinder, a disk, and a truncated cone. In all cases the partition function evolves according to a linear diffusion-type equation, and the deformation may be viewed as a kind of random walk in moduli space in which domains shrink and become more symmetrical. The truncated cone allows access to information about the behavior of correlations, and of entanglement entropies, under the deformation. We also suggest a generalization of the whole formalism to higher dimensions.

  • Holographic superconductor with nonlinear arcsin-electrodynamics.- [PDF] - [Article]

    S. I. Kruglov

    We investigate holographic s-wave superconductors with nonlinear arcsin-electrodynamics in the background of Schwarzschild anti-de Sitter black holes. The analytical Sturm-Liouville eigenvalue problem is explored and we imply that the scalar and electromagnetic fields do not influence on the background metric (the probe limit). The critical temperatures of phase transitions depending on the parameter of the model is obtained. We show that in our case the condensation formation becomes easier compared to Born-Infeld nonlinear electrodynamics. The critical exponent near the critical temperature is calculated which is 1/2.

  • Spin Geometry and Some Applications.- [PDF] - [Article]

    Ümit Ertem

    In this review, basic definitions of spin geometry are given and some of its applications to supersymmetry, supergravity and condensed matter physics are summarized. Clifford algebras and spinors are defined and the first-order differential operators on spinors which lead to the definitions of twistor and Killing spinors are discussed. Holonomy classification for manifolds admitting parallel and Killing spinors are given. Killing-Yano and conformal Killing-Yano forms resulting from the spinor bilinears of Killing and twistor spinors are introduced and the symmetry operators of special spinor equations are constructed in terms of them. Spinor bilinears and symmetry operators are used for constructing the extended superalgebras from twistor and Killing spinors. A method to obtain harmonic spinors from twistor spinors and potential forms is given and its implications on finding solutions of the Seiberg-Witten equations are discussed. Supergravity Killing spinors defined in bosonic supergravity theories are considered and possible Lie algebra structures satisfied by their spinor bilinears are examined. Spin raising and lowering operators for massless field equations with different spins are constructed and the case for Rarita-Schwinger fields is investigated. The derivation of the periodic table of topological insulators and superconductors in terms of Clifford chessboard and index of Dirac operators is summarized.

  • A fermionic code related to the exceptional group $E_8$.- [PDF] - [Article]

    Péter Lévay, Frédéric Holweck

    In this paper we study the Hamming-like fermionic code encoding three-qubits into sixteen Majorana modes recently introduced by Hastings. We show that although this fermionic code cannot be obtained from a single qubit stabilizer code via the usual procedure however, it can be obtained from two, qubit stabilizer ones via a glueing procedure combining both single and double occupancy embeddings of qubits into fermionic Fock space. This technique identifies the code subspace as a Cartan subspace of the largest exceptional group $E_8$. In arriving at these results we develop a general formalism for implementing this glueing procedure via the use of intertwiners between different subsectors of the Fock space realizing embedded qubits.

  • Bootstrapping hypercubic and hypertetrahedral theories in three dimensions.- [PDF] - [Article]

    Andreas Stergiou

    There are three generalizations of the Platonic solids that exist in all dimensions, namely the hypertetrahedron, the hypercube, and the hyperoctahedron, with the latter two being dual. Conformal field theories with the associated symmetry groups as global symmetries can be argued to exist in $d=3$ spacetime dimensions if the $\varepsilon=4-d$ expansion is valid when $\varepsilon\to1$. In this paper hypercubic and hypertetrahedral theories are studied with the non-perturbative numerical conformal bootstrap. In the $N=3$ cubic case it is found that a bound with a kink is saturated by a solution with properties that cannot be reconciled with the $\varepsilon$ expansion of the cubic theory. Possible implications for cubic magnets and structural phase transitions are discussed. For the hypertetrahedral theory evidence is found that the non-conformal window that is seen with the $\varepsilon$ expansion exists in $d=3$ as well, and a rough estimate of its extent is given.

  • Scale-invariant Feature Extraction of Neural Network and Renormalization Group Flow.- [PDF] - [Article]

    Satoshi Iso, Shotaro Shiba, Sumito Yokoo

    Theoretical understanding of how deep neural network (DNN) extracts features from input images is still unclear, but it is widely believed that the extraction is performed hierarchically through a process of coarse-graining. It reminds us of the basic concept of renormalization group (RG) in statistical physics. In order to explore possible relations between DNN and RG, we use the Restricted Boltzmann machine (RBM) applied to Ising model and construct a flow of model parameters (in particular, temperature) generated by the RBM. We show that the unsupervised RBM trained by spin configurations at various temperatures from $T=0$ to $T=6$ generates a flow along which the temperature approaches the critical value $T_c=2.27$. This behavior is opposite to the typical RG flow of the Ising model. By analyzing various properties of the weight matrices of the trained RBM, we discuss why it flows towards $T_c$ and how the RBM learns to extract features of spin configurations.

  • Polyadic systems, representations and quantum groups.- [PDF] - [Article] - [UPDATED]

    Steven Duplij

    Polyadic systems and their representations are reviewed and a classification of general polyadic systems is presented. A new multiplace generalization of associativity preserving homomorphisms, a 'heteromorphism' which connects polyadic systems having unequal arities, is introduced via an explicit formula, together with related definitions for multiplace representations and multiactions. Concrete examples of matrix representations for some ternary groups are then reviewed. Ternary algebras and Hopf algebras are defined, and their properties are studied. At the end some ternary generalizations of quantum groups and the Yang-Baxter equation are presented.

  • Chiral algebras in Landau-Ginzburg models.- [PDF] - [Article] - [UPDATED]

    Mykola Dedushenko

    Chiral algebras in the cohomology of the $\overline{Q}_+$ supercharge of two-dimensional $\mathcal{N}=(0,2)$ theories on flat spacetime are discussed. Using the supercurrent multiplet, we show that the answer is renormalization group invariant for theories with an R-symmetry. For $\mathcal{N}=(0,2)$ Landau-Ginzburg models, the chiral algebra is determined by the operator equations of motion, which preserve their classical form, and quantum renormalization of composite operators. We study these theories and then specialize to the $\mathcal{N}=(2,2)$ models and consider some examples.

  • Stable spherically symmetric monopole field background in a pure QCD.- [PDF] - [Article] - [UPDATED]

    Youngman Kim, Bum-Hoon Lee, D.G. Pak, Takuya Tsukioka

    We consider a stationary spherically symmetric monopole like solution with a finite energy density in a pure quantum chromodynamics (QCD). The solution can be treated as a static Wu-Yang monopole dressed in time dependent field corresponding to off-diagonal gluons. We have proved that such a stationary monopole field represents a background vacuum field of the QCD effective action which is stable against quantum gluon fluctuations. This resolves a long-standing problem of existence of a stable vacuum field in QCD and opens a new avenue towards microscopic theory of the vacuum.

  • The Global Gauge Group Structure of F-theory Compactification with U(1)s.- [PDF] - [Article] - [UPDATED]

    Mirjam Cvetic, Ling Lin

    We show that F-theory compactifications with abelian gauge factors generally exhibit a non-trivial global gauge group structure. The geometric origin of this structure lies with the Shioda map of the Mordell--Weil generators. This results in constraints on the U(1) charges of non-abelian matter consistent with observations made throughout the literature. In particular, we find that F-theory models featuring the Standard Model algebra actually realise the precise gauge group [SU(3)xSU(2)xU(1)]/Z6. Furthermore, we explore the relationship between the gauge group structure and geometric (un-)higgsing. In an explicit class of models, we show that, depending on the global group structure, an SU(2)xU(1) gauge theory can either unhiggs into an SU(2)xSU(2) or an SU(3)xSU(2) theory. We also study implications of the charge constraints as a criterion for the F-theory 'swampland'.

  • Edge insulating topological phases in a two-dimensional long-range superconductor.- [PDF] - [Article] - [UPDATED]

    L. Lepori, D. Giuliano, S. Paganelli

    We study the zero-temperature phase diagram of a two dimensional square lattice loaded by spinless fermions, with nearest neighbor hopping and algebraically decaying pairing. We find that for sufficiently long-range pairing, new phases, not continuously connected with any short-range phase, occur, signaled by the violation of the area law for the Von Neumann entropy, by semi-integer Chern numbers, and by edge modes with nonzero mass. The latter feature results in the absence of single-fermion edge conductivity, present instead in the short- range limit. The definition of a topology in the bulk and the presence of a bulk-boundary correspondence is still suggested for the long-range phases. Recent experimental proposals and advances open the stimulating possibility to probe the described long-range effects in next-future realistic set-ups.

  • Black hole entropy in massive Type IIA.- [PDF] - [Article] - [UPDATED]

    Francesco Benini, Hrachya Khachatryan, Paolo Milan

    We study the entropy of static dyonic BPS black holes in AdS$_4$ in 4d $\mathcal{N}=2$ gauged supergravities with vector and hyper multiplets, and how the entropy can be reproduced with a microscopic counting of states in the AdS/CFT dual field theory. We focus on the particular example of BPS black holes in AdS$_4 \times S^6$ in massive Type IIA, whose dual three-dimensional boundary description is known and simple. To count the states in field theory we employ a supersymmetric topologically twisted index, which can be computed exactly with localization techniques. We find perfect match at leading order.

  • Modified Wigner equations and continuous spin gauge field.- [PDF] - [Article] - [UPDATED]

    Mojtaba Najafizadeh

    In this paper, we first propose the bosonic (fermionic) modified Wigner equations for continuous spin particle (CSP). Secondly, starting from the (Fang-)Fronsdal-like equation, we will reach to the modified action of bosonic (fermionic) continuous spin gauge field in flat spacetime, presented recently by Metsaev in A(dS) spacetime. We shall also explain how to obtain the proposed modified Wigner equations from the gauge-fixed equations of motion. Finally, we will consider the massive bosonic (fermionic) higher-spin action and, by taking the infinite spin limit, we will arrive at the modified bosonic (fermionic) CSP action.

  • Conformal Bootstrap Analysis for Single and Branched Polymers.- [PDF] - [Article] - [UPDATED]

    S. Hikami

    The conformal bootstrap theory is studied by the determinantal method for the self-avoiding walk, which is equivalent to a dilute polymer in a solvent. The equivalence of the branched polymer in D dimensions to Yang-Lee edge singularity in D-2 dimensions is discussed by the determinantal method with the use of the N=0 limit in O(N) vector model.

  • Fermionic spinon theory of square lattice spin liquids near the N\'eel state.- [PDF] - [Article] - [UPDATED]

    Alex Thomson, Subir Sachdev

    Quantum fluctuations of the N\'eel state of the square lattice antiferromagnet are usually described by a $\mathbb{CP}^1$ theory of bosonic spinons coupled to a U(1) gauge field, and with a global SU(2) spin rotation symmetry. Such a theory also has a confining phase with valence bond solid (VBS) order, and upon including spin-singlet charge 2 Higgs fields, deconfined phases with $\mathbb{Z}_2$ topological order possibly intertwined with discrete broken global symmetries. We present dual theories of the same phases starting from a mean-field theory of fermionic spinons moving in $\pi$-flux in each square lattice plaquette. Fluctuations about this $\pi$-flux state are described by 2+1 dimensional quantum chromodynamics (QCD$_3$) with a SU(2) gauge group and $N_f=2$ flavors of massless Dirac fermions. It has recently been argued by Wang et al. (arXiv:1703.02426) that this QCD$_3$ theory describes the N\'eel-VBS quantum phase transition. We introduce adjoint Higgs fields in QCD$_3$, and obtain fermionic dual descriptions of the phases with $\mathbb{Z}_2$ topological order obtained earlier using the bosonic $\mathbb{CP}^1$ theory. We also present a fermionic spinon derivation of the monopole Berry phases in the U(1) gauge theory of the VBS state. The global phase diagram of these phases contains multi-critical points, and our results imply new boson-fermion dualities between critical gauge theories of these points.

  • Black hole elasticity and gapped transverse phonons in holography.- [PDF] - [Article] - [UPDATED]

    Lasma Alberte, Martin Ammon, Matteo Baggioli, Amadeo Jiménez, Oriol Pujolàs

    We study the elastic response of planar black hole (BH) solutions in a simple class of holographic models with broken translational invariance. We compute the transverse quasi-normal mode spectrum and the propagation speed of the lowest energy mode. We find that the speed of the lowest mode relates to the BH rigidity modulus as dictated by elasticity theory. This allows to identify these modes as transverse phonons---the pseudo Goldstone bosons of spontaneously broken translational invariance. In addition, we show that these modes have a mass gap controlled by an explicit source of the translational symmetry breaking. These results provide a new confirmation that the BHs in these models do exhibit solid properties that become more manifest at low temperatures. Also, by the AdS/CFT correspondence, this allows to extend the standard results from the effective field theory for solids to quantum-critical materials.

  • Quantum Energy Teleportation in Two-dimensional Conformal Field Theories.- [PDF] - [Article] - [UPDATED]

    Wu-Zhong Guo, Feng-Li Lin

    We construct a set of quasi-local measurement operators in 2D CFT, and then use them to proceed the quantum energy teleportation (QET) protocol and show it is viable. These measurement operators are constructed out of the projectors constructed from shadow operators, but further acting on the product of two spatially separated primary fields. They are equivalently the OPE blocks in the large central charge limit up to some UV-cutoff dependent normalization. However, we show that the probabilities of their measurement outcomes are UV-cutoff independent. Furthermore, we also demonstrate that despite of their quasi-locality, the OPE blocks do satisfy the causality constraints. To show the essence of quantum entanglement for the viability of QET, we prove a no-go theorem if taking the long time limit $T\to \infty$, where $T$ is the time duration between Alice's and Bob's operation. Beyond this limit we find the QET can be successfully realized. In contrast, we find that these measurement operators cannot violate CHSH inequality.

  • T-duality invariant effective actions at orders $ \alpha', \alpha'^2$.- [PDF] - [Article] - [UPDATED]

    Hamid Razaghian, Mohammad R. Garousi

    We use compatibility of the $D$-dimensional effective actions for diagonal metric and for dilaton with the T-duality when theory is compactified on a circle, to find the the $D$-dimensional couplings of curvatures and dilaton as well as the higher derivative corrections to the $(D-1)$-dimensional Buscher rules at orders $ \alpha' $ and $\alpha'^2$. We observe that the T-duality constraint on the effective actions fixes the covariant effective actions at each order of $\alpha'$ up to field redefinitions and up to an overall factor. Inspired by these results, we speculate that the $D$-dimensional effective actions at any order of $\alpha'$ must be consistent with the standard Buscher rules provided that one uses covariant field redefinitions in the corresponding reduced $(D-1)$-dimensional effective actions. This constraint may be used to find effective actions at all higher orders of $\alpha'$.

  • Simplifying large spin bootstrap in Mellin space.- [PDF] - [Article] - [UPDATED]

    Parijat Dey, Kausik Ghosh, Aninda Sinha

    We set up the conventional conformal bootstrap equations in Mellin space and analyse the anomalous dimensions and OPE coefficients of large spin double trace operators. By decomposing the equations in terms of continuous Hahn polynomials, we derive explicit expressions as an asymptotic expansion in inverse conformal spin to any order, reproducing the contribution of any primary operator and its descendants in the crossed channel. The expressions are in terms of known mathematical functions and involve generalized Bernoulli (Norlund) polynomials and the Mack polynomials and enable us to derive certain universal properties. Comparing with the recently introduced reformulated equations in terms of crossing symmetric tree level exchange Witten diagrams, we show that to leading order in anomalous dimension but to all orders in inverse conformal spin, the equations are the same as in the conventional formulation. At the next order, the polynomial ambiguity in the Witten diagram basis is needed for the equivalence and we derive the necessary constraints for the same.

  • Chiral Higher Spin Theories and Self-Duality.- [PDF] - [Article] - [UPDATED]

    Dmitry Ponomarev

    We study recently proposed chiral higher spin theories - cubic theories of interacting massless higher spin fields in four-dimensional flat space. We show that they are naturally associated with gauge algebras, which manifest themselves in several related ways. Firstly, the chiral higher spin equations of motion can be reformulated as the self-dual Yang-Mills equations with the associated gauge algebras instead of the usual colour gauge algebra. We also demonstrate that the chiral higher spin field equations, similarly to the self-dual Yang-Mills equations, feature an infinite algebra of hidden symmetries, which ensures their integrability. Secondly, we show that off-shell amplitudes in chiral higher spin theories satisfy the generalised BCJ relations with the usual colour structure constants replaced by the structure constants of higher spin gauge algebras. We also propose generalised double copy procedures featuring higher spin theory amplitudes. Finally, using the light-cone deformation procedure we prove that the structure of the Lagrangian that leads to all these properties is universal and follows from Lorentz invariance.

  • A Note on (Non)-Locality in Holographic Higher Spin Theories.- [PDF] - [Article] - [UPDATED]

    Dmitry Ponomarev

    It was argued recently that the holographic higher spin theory features non-local interactions. We further elaborate on these results using the Mellin representation. The main difficulty previously encountered on this way is that the Mellin amplitude for the free theory correlator is ill-defined. To resolve this problem, instead of literally applying the standard definition, we propose to define this amplitude by linearity using decompositions, where each term has the associated Mellin amplitude well-defined. Up to a sign, the resulting amplitude is equal to the Mellin amplitude for the singular part of the quartic vertex in the bulk theory and, hence, can be used to analyze bulk locality. From this analysis we find that the scalar quartic self-interaction vertex in the holographic higher spin theory has a singularity of a special form, which can be distinguished from generic bulk exchanges. We briefly discuss the physical interpretation of such singularities and their relation to the Noether procedure.

  • Spheres, Charges, Instantons, and Bootstrap: A Five-Dimensional Odyssey.- [PDF] - [Article] - [UPDATED]

    Chi-Ming Chang, Martin Fluder, Ying-Hsuan Lin, Yifan Wang

    We combine supersymmetric localization and the conformal bootstrap to study five-dimensional superconformal field theories. To begin, we classify the admissible counter-terms and derive a general relation between the five-sphere partition function and the conformal and flavor central charges. Along the way, we discover a new superconformal anomaly in five dimensions. We then propose a precise triple factorization formula for the five-sphere partition function, that incorporates instantons and is consistent with flavor symmetry enhancement. We numerically evaluate the central charges for the rank-one Seiberg and Morrison-Seiberg theories, and find strong evidence for their saturation of bootstrap bounds, thereby determining the spectra of long multiplets in these theories. Lastly, our results provide new evidence for the $F$-theorem and possibly a $C$-theorem in five-dimensional superconformal theories.

  • Asymmetric hermitian matrix models and fuzzy field theory.- [PDF] - [Article] - [UPDATED]

    Juraj Tekel

    We analyze two types of hermitian matrix models with asymmetric solutions. One type breaks the symmetry explicitly with an asymmetric quartic potential. We give the phase diagram of this model with two different phase transitions between the one cut and two cut solutions. The second type, describing real scalar field theory on fuzzy spaces, breaks the symmetry spontaneously with multitrace terms. We present two methods to study this model, one direct and one using a connection with the first type of models. We analyze the model for the fuzzy sphere and obtain a phase diagram with a refined location of the triple point, which is in a good agreement with the most recent numerical simulations.

  • Lifshitz entanglement entropy from holographic cMERA.- [PDF] - [Article] - [UPDATED]

    Simon A. Gentle, Stefan Vandoren

    We study entanglement entropy in free Lifshitz scalar field theories holographically by employing the metrics proposed by Nozaki, Ryu and Takayanagi in \cite{Nozaki:2012zj} obtained from a continuous multi-scale entanglement renormalisation ansatz (cMERA). In these geometries we compute the minimal surface areas governing the entanglement entropy as functions of the dynamical exponent $z$ and we exhibit a transition from an area law to a volume law analytically in the limit of large $z$. We move on to explore the effects of a massive deformation, obtaining results for any $z$ in arbitrary dimension. We then trigger a renormalisation group flow between a Lifshitz theory and a conformal theory and observe a monotonic decrease in entanglement entropy along this flow. We focus on strip regions but also consider a disc in the undeformed theory.

  • Three-dimensional dualities with bosons and fermions.- [PDF] - [Article] - [UPDATED]

    Francesco Benini

    We propose new infinite families of non-supersymmetric IR dualities in three space-time dimensions, between Chern-Simons gauge theories (with classical gauge groups) with both scalars and fermions in the fundamental representation. In all cases we study the phase diagram as we vary two relevant couplings, finding interesting lines of phase transitions. In various cases the dualities lead to predictions about multi-critical fixed points and the emergence of IR quantum symmetries. For unitary groups we also discuss the coupling to background gauge fields and the map of simple monopole operators.

  • Romans Supergravity from Five-Dimensional Holograms.- [PDF] - [Article] - [UPDATED]

    Chi-Ming Chang, Martin Fluder, Ying-Hsuan Lin, Yifan Wang

    We study five-dimensional superconformal field theories and their holographic dual, matter-coupled Romans supergravity. On the one hand, some recently derived formulae allow us to extract the central charges from deformations of the supersymmetric five-sphere partition function, whose large N expansion can be computed using matrix model techniques. On the other hand, the conformal and flavor central charges can be extracted from the six-dimensional supergravity action, by carefully analyzing its embedding into type I' string theory. The results match on the two sides of the holographic duality. Our results also provide analytic evidence for the symmetry enhancement in five-dimensional superconformal field theories.

  • Generalised global symmetries in states with dynamical defects: the case of the transverse sound in field theory and holography.- [PDF] - [Article] - [UPDATED]

    Sašo Grozdanov, Napat Poovuttikul

    In this work, we show how states with conserved numbers of dynamical defects (strings, domain walls, etc.) can be understood as possessing generalised global symmetries even when the microscopic origins of these symmetries are unknown. Using this philosophy, we build an effective theory of a $2+1$-dimensional fluid state with two perpendicular sets of immersed elastic line defects. When the number of defects is independently conserved in each set, then the state possesses two one-form symmetries. Normally, such viscoelastic states are described as fluids coupled to Goldstone bosons associated with spontaneous breaking of translational symmetry caused by the underlying microscopic structure---the principle feature of which is a transverse sound mode. At the linear, non-dissipative level, we verify that our theory, based entirely on symmetry principles, is equivalent to a viscoelastic theory. We then build a simple holographic dual of such a state containing dynamical gravity and two two-form gauge fields, and use it to study its hydrodynamic and higher-energy spectral properties characterised by non-hydrodynamic, gapped modes. Based on the holographic analysis of transverse two-point functions, we study consistency between low-energy predictions of the bulk theory and the effective boundary theory. Various new features of the holographic dictionary are explained in theories with higher-form symmetries, such as the mixed-boundary-condition modification of the quasinormal mode prescription that depends on the running coupling of the boundary double-trace deformations. Furthermore, we examine details of low- and high-energy parts of the spectrum that depend on temperature, line defect densities and the renormalisation group scale (dimensional transmutation).

  • Thermoelectric DC conductivities in hyperscaling violating Lifshitz theories.- [PDF] - [Article] - [UPDATED]

    Sera Cremonini, Mirjam Cvetič, Ioannis Papadimitriou

    We analytically compute the thermoelectric conductivities at zero frequency (DC) in the holographic dual of a four dimensional Einstein-Maxwell-Axion-Dilaton theory that admits a class of asymptotically hyperscaling violating Lifshitz backgrounds with a dynamical exponent $z$ and hyperscaling violating parameter $\theta$. We show that the heat current in the dual Lifshitz theory involves the energy flux, which is an irrelevant operator for $z>1$. The linearized fluctuations relevant for computing the thermoelectric conductivities turn on a source for this irrelevant operator, leading to several novel and non-trivial aspects in the holographic renormalization procedure and the identification of the physical observables in the dual theory. Moreover, imposing Dirichlet or Neumann boundary conditions on the spatial components of one of the two Maxwell fields present leads to different thermoelectric conductivities. Dirichlet boundary conditions reproduce the thermoelectric DC conductivities obtained from the near horizon analysis of Donos and Gauntlett, while Neumann boundary conditions result in a new set of DC conductivities. We make preliminary analytical estimates for the temperature behavior of the thermoelectric matrix in appropriate regions of parameter space. In particular, at large temperatures we find that the only case which could lead to a linear resistivity $\rho \sim T$ corresponds to $z=4/3$.


  • Continuous-variable gate decomposition for the Bose-Hubbard model.- [PDF] - [Article]

    Timjan Kalajdzievski, Christian Weedbrook, Patrick Rebentrost

    In this work, we decompose the time-evolution of the Bose-Hubbard model into a sequence of logic gates that can be implemented on a continuous-variable photonic quantum computer. We examine the structure of the circuit that represents this time-evolution for one-dimensional and two-dimensional lattices. The elementary gates needed for the implementation are counted as a function of lattice size. We also include the contribution of the leading dipole interaction term which may be added to the Hamiltonian, and its corresponding circuit.

  • Towards practical high-speed high dimensional quantum key distribution using partial mutual unbiased basis of photon's orbital angular momentum.- [PDF] - [Article]

    Fumin Wang, Pei Zeng, Xiaoli Wang, Hong Gao, Fuli Li, Pei Zhang

    Quantum Key Distribution (QKD) guarantees the security of communication with quantum physics. Most of widely adopted QKD protocols currently encode the key information with binary signal format---qubit, such as the polarization states. Therefore the transmitted information efficiency of the quantum key is intrinsically upper bounded by 1 bit per photon. High dimensional quantum system is a potential candidate for increasing the capacity of single photon. However, due to the difficulty in manipulating and measuring high dimensional quantum systems, the experimental high dimensional QKD is still at its infancy. Here we propose a sort of practical high-speed high dimensional QKD using partial mutual unbiased basis (PMUB) of photon's orbital angular momentum (OAM). Different from the previous OAM encoding, the high dimensional Hilbert space we used is expanded by the OAM states with same mode order, which can be extended to considerably high dimensions and implemented under current state of the art. Because all the OAM states are in the same mode order, the coherence will be well kept after long-distance propagation, and the detection can be achieved by using passive linear optical elements with very high speed. We show that our protocol has high key generation rate and analyze the anti-noise ability under atmospheric turbulence. Furthermore, the security of our protocol based on PMUB is rigorously proved. Our protocol paves a brand new way for the application of photon's OAM in high dimensional QKD field, which can be a breakthrough for high efficiency quantum communications.

  • Attaining the quantum limit of super resolution in imaging an object's length via pre-detection spatial mode sorting.- [PDF] - [Article]

    Zachary Dutton, Ronan Kerviche, Amit Ashok, Saikat Guha

    Recent work considered the ultimate (quantum) limit of the precision of estimating the distance between two point objects. It was shown that the performance gap between the quantum limit and that of ideal continuum image-plane direct detection is the largest for highly sub-Rayleigh separation of the objects, and that a pre-detection mode sorting could attain the quantum limit. Here we extend this to a more general problem of estimating the length of an incoherently radiating extended (line) object. We find, as expected by the Rayleigh criterion, the Fisher information (FI) per integrated photon vanishes in the limit of small length for ideal image plane direct detection. Conversely, for a Hermite-Gaussian (HG) pre-detection mode sorter, this normalized FI does not decrease with decreasing object length, similar to the two point object case. However, unlike in the two-object problem, the FI per photon of both detection strategies gradually decreases as the object length greatly exceeds the Rayleigh limit, due to the relative inefficiency of information provided by photons emanating from near the center of the object about its length. We evaluate the quantum Fisher information per unit integrated photons and find that the HG mode sorter exactly achieves this limit at all values of the object length. Further, a simple binary mode sorter maintains the advantage of the full mode sorter at highly sub-Rayleigh length. In addition to this FI analysis, we quantify improvement in terms of the actual mean squared error of the length estimate. Finally, we consider the effect of imperfect mode sorting, and show that the performance improvement over direct detection is robust over a range of sub-Rayleigh lengths.

  • Strain-tunable GaAs quantum dot: An on-demand source of nearly-maximally entangled photon pairs.- [PDF] - [Article]

    Daniel Huber, Marcus Reindl, Saimon Filipe Covre da Silva, Christian Schimpf, Javier Martin-Sanchez, Giovanni Piredda, Johannes Edlinger, Armando Rastelli, Rinaldo Trotta

    Entangled photon generation from semiconductor quantum dots via the biexciton-exciton cascade underlies various decoherence mechanisms related to the solid-state nature of the quantum emitters. So far, this has prevented the demonstration of nearly-maximally entangled photons without the aid of inefficient and complex post-selection techniques that are hardly suitable for quantum communication technologies. Here, we tackle this challenge using strain-tunable GaAs quantum dots driven under two-photon resonant excitation and with strictly-degenerate exciton states. We demonstrate experimentally that our on-demand source generates polarization-entangled photons with fidelity of 0.978(5) and concurrence of 0.97(1) without resorting to post-selection techniques. Moreover, we show that the remaining decoherence mechanisms can be overcome using a modest Purcell enhancement so as to achieve a degree of entanglement >0.99. Our results highlight that GaAs quantum dots can be readily used in advanced communication protocols relying on the non-local properties of quantum entanglement.

  • Orbital state manipulation of a diamond nitrogen-vacancy center using a mechanical resonator.- [PDF] - [Article]

    H.Y. Chen, E. R. MacQuarrie, G. D. Fuchs

    We study the resonant optical transitions of a single nitrogen-vacancy (NV) center that is coherently dressed by a strong mechanical drive. Using a gigahertz-frequency diamond mechanical resonator that is strain-coupled to an NV center's orbital states, we demonstrate coherent Raman sidebands out to the ninth order and orbital-phonon interactions that mix the two excited-state orbital branches. These interactions are spectroscopically revealed through a multi-phonon Rabi splitting of the orbital branches which scales as a function of resonator driving amplitude, and is successfully reproduced in a quantum model. Finally, we discuss the application of mechanical driving to engineering NV center orbital states.

  • $\mathcal {PT}$-symmetric circuit-QED.- [PDF] - [Article]

    Fernando Quijandría, Uta Naether, Sahin K. Özdemir, Franco Nori, David Zueco

    The Hermiticity axiom of quantum mechanics guarantees that the energy spectrum is real and the time evolution is unitary (probability-preserving). Nevertheless, non-Hermitian but $\mathcal{PT}$-symmetric Hamiltonians may also have real eigenvalues. Systems described by such effective $\mathcal {PT}$-symmetric Hamiltonians have been realized in experiments using coupled systems with balanced loss (dissipation) and gain (amplification), and their corresponding classical dynamics has been studied. A $\mathcal {PT}$-symmetric system emerging from a quantum dynamics is highly desirable, in order to understand what $\mathcal {PT}$-symmetry and the powerful mathematical and physical concepts around it will bring to the next generation of quantum technologies. Here, we address this need by proposing and studying a circuit-QED architecture that consists of two coupled resonators and two qubits (each coupled to one resonator). By means of external driving fields on the qubits, we are able to tune gain and losses in the resonators. Starting with the quantum dynamics of this system, we show the emergence of the $\mathcal {PT}$-symmetry via the selection of both driving amplitudes and frequencies. We engineer the system such that a non-number conserving dipole-dipole interaction emerges, introducing an instability at large coupling strengths. The $\mathcal {PT}$-symmetry and its breaking, as well as the predicted instability in this circuit-QED system can be observed in a transmission experiment.

  • One way quantum repeaters with quantum Reed-Solomon codes.- [PDF] - [Article]

    Sreraman Muralidharan, Chang-Ling Zou, Linshu Li, Liang Jiang

    We show that quantum Reed-Solomon codes constructed from classical Reed-Solomon codes can approach the capacity on the quantum erasure channel of $d$-level systems for large dimension $d$. We study the performance of one-way quantum repeaters with these codes and obtain a significant improvement in key generation rate compared to previously investigated encoding schemes with quantum parity codes and quantum polynomial codes. We also compare the three generation of quantum repeaters using quantum Reed-Solomon codes and identify parameter regimes where each generation performs the best.

  • Entanglement between total intensity and polarization for pair coherent states.- [PDF] - [Article]

    Carlos Sanchidrián-Vaca, Alfredo Luis

    We examine entanglement for number-polarization, or number and relative phase, in pair coherent states and two-mode squeezed vacuum via linear entropy and covariance criteria. We show that variable-like entanglement as measured by covariance criteria is isomorphic to particle-like entanglement. We consider the embedding of the two-mode Hilbert space in a larger space to get a well-defined factorization of the number-phase variables revealing proper entanglement for the coherent states.

  • Universal Origin for Environment-Assisted Quantum Transport in Exciton Transfer Networks.- [PDF] - [Article]

    Elinor Zerah-Harush, Yonatan Dubi

    Environment-assisted quantum transport (ENAQT) is the possibility of an external environment to enhance transport efficiency of quantum particles. This idea has generated much excitement over recent years, especially due to the experimentally-motivated possibility of ENAQT in photo-synthetic exciton transfer complexes. Many theoretical calculations have shown ENAQT, but the explanations for its origin differ, and a universal explanation has been elusive. Here we demonstrate a universal origin for ENAQT in quantum networks with a dephasing environment, based on a relation between exciton current and occupation within a Markovian open quantum system approach. We show that ENAQT appears due to two competing processes, namely the tendency of dephasing to make the exciton population uniform, and the formation of an exciton density gradient, defined by the source and the sink. Furthermore, we find a geometric condition on the network for the appearance of ENAQT, relevant to natural and artificial systems.

  • Direct observation of atom-ion non-equilibrium sympathetic cooling.- [PDF] - [Article]

    Ziv Meir, Meirav Pinkas, Tomas Sikorsky, Ruti Ben-shlomi, Nitzan Akerman, Roee Ozeri

    Sympathetic cooling is the process of energy exchange between a system and a colder bath. We investigate this fundamental process in an atom-ion experiment where the system is composed of a single ion, trapped in a radio-frequency Paul trap, and prepared in a coherent state of ~200 K and the bath is an ultracold cloud of atoms at {\mu}K temperature. We directly observe the sympathetic cooling dynamics with single-shot energy measurements during one, to several, collisions in two distinct regimes. In one, collisions predominantly cool the system with very efficient momentum transfer leading to cooling in only a few collisions. In the other, collisions can both cool and heat the system due to the non-equilibrium dynamics of the atom-ion collisions in the presence of the ion-trap's oscillating electric fields. While the bulk of our observations agree well with a molecular dynamics simulation of hard-sphere (Langevin) collisions, a measurement of the scattering angle distribution reveals forward-scattering (glancing) collisions which are beyond the Langevin model. This work paves the way for further non-equilibrium and collision dynamics studies using the well-controlled atom-ion system.

  • Bulk Heating Effects as Tests for Collapse Models.- [PDF] - [Article]

    Stephen L. Adler, Andrea Vinante

    We discuss limits on the noise strength parameter in wave function collapse models implied by bulk heating effects, and examine the role of the noise power spectrum in comparing experiments of different types. We suggest possible new bulk heating experiments that can be performed subject to limits placed by natural heating from radioactivity and cosmic rays. The proposed experiments exploit the vanishing of thermal transport in the low temperature limit.

  • Two-photon processes based on quantum commutators.- [PDF] - [Article]

    Filippo Fratini, Laleh Safari, Pedro Amaro, José-Paulo Santos

    We developed a new method to calculate two-photon processes in quantum mechanics that replaces the infinite summation over the intermediate states by a perturbation expansion. This latter consists of a series of commutators that involve position, momentum and hamiltonian quantum operators. We analyzed several single- and many-particle cases for which a closed form solution to the perturbation expansion exists, as well as more complicated cases for which a solution is found by convergence. Throughout the article, Rayleigh and Raman scattering are taken as examples of two-photon processes. The present method provides a clear distinction between the Thomson scattering, regarded as classical scattering, and quantum contributions. Such a distinction let us derive general results concerning light scattering. Finally, possible extensions to the developed formalism are discussed.

  • Quantum fluctuation theorem to benchmark quantum annealers.- [PDF] - [Article]

    Bartłomiej Gardas, Sebastian Deffner

    Near term quantum hardware promises unprecedented computational advantage. Crucial in its development is the characterization and minimization of computational errors. We propose the use of the quantum fluctuation theorem to benchmark the performance of quantum annealers. This versatile tool provides simple means to determine whether the quantum dynamics are unital, unitary, and adiabatic, or whether the system is prone to thermal noise. Our proposal is experimentally tested on two generations of the D-Wave machine, which illustrates the sensitivity of the fluctuation theorem to the smallest aberrations from ideal annealing.

  • Multiplexed Quantum Random Number Generation.- [PDF] - [Article]

    Ben Haylock, Daniel Peace, Francesco Lenzini, Christian Weedbrook, Mirko Lobino

    Fast secure random number generation is essential for high-speed encrypted communication, and is the backbone of information security. Generation of truly random numbers depends on the intrinsic randomness of the process used and is usually limited by electronic bandwidth and signal processing data rates. Here we use a multiplexing scheme to create a fast quantum random number generator structurally tailored to encryption for distributed computing, and high bit-rate data transfer. We use vacuum fluctuations measured by seven homodyne detectors as quantum randomness sources, multiplexed using a single integrated optical device. We obtain a random number generation rate of 3.08 Gbit/s, from only 27.5 MHz of sampled detector bandwidth. Furthermore, we take advantage of the multiplexed nature of our system to demonstrate an unseeded strong extractor with a generation rate of 26 Mbit/s.

  • Totally Destructive Many-Particle Interference.- [PDF] - [Article]

    Christoph Dittel, Gabriel Dufour, Mattia Walschaers, Gregor Weihs, Andreas Buchleitner, Robert Keil

    In a general, multi-mode scattering setup, we show how the permutation symmetry of a many-particle input state determines those scattering unitaries which exhibit strictly suppressed many-particle transition events. We formulate purely algebraic suppression laws that identify these events and show that the many-particle interference at their origin is robust under weak disorder and imperfect indistinguishability of the interfering particles. Finally, we demonstrate that all suppression laws so far described in the literature are embedded in the general framework that we here introduce.

  • Totally Destructive Interference for Permutation-Symmetric Many-Particle States.- [PDF] - [Article]

    Christoph Dittel, Gabriel Dufour, Mattia Walschaers, Gregor Weihs, Andreas Buchleitner, Robert Keil

    Several distinct classes of unitary mode transformations have been known to exhibit the strict suppression of a large set of transmission events, as a consequence of totally destructive many-particle interference. In [Dittel et al., Totally Destructive Many-Particle Interference] we unite these cases by identifying a general class of unitary matrices which exhibit such interferences. Here, we provide a detailed theoretical analysis that substantially expands on all aspects of this generalisation: We prove the suppression laws put forward in [Dittel et al., Totally Destructive Many-Particle Interference], establish how they interrelate with forbidden single-particle transitions, show how all suppression laws hitherto known can be retrieved from our general formalism, and discuss striking differences between bosons and fermions. Furthermore, beyond many-particle Fock states on input, we consider arbitrary pure initial states and derive suppression laws which stem from the wave function's permutation symmetry alone. Finally, we identify conditions for totally destructive interference to persist when the involved particles become partially distinguishable.

  • Real-Time Dynamics of Typical and Untypical States in Non-Integrable Systems.- [PDF] - [Article]

    Jonas Richter, Fengping Jin, Hans De Raedt, Kristel Michielsen, Jochen Gemmer, Robin Steinigeweg

    For a class of typical states, the real-time and real-space dynamics of non-equilibrium density profiles has been recently studied for integrable models, i.e. the spin-1/2 XXZ chain [PRB 95, 035155 (2017)] and the Fermi-Hubbard chain [PRE 96, 020105 (2017)]. It has been found that the non-equilibrium dynamics agrees with linear response theory. Moreover, in the regime of strong interactions, clear signatures of diffusion have been observed. However, this diffusive behavior strongly depends on the choice of the initial state and disappears for untypical states without internal randomness. In the present work, we address the question whether or not the above findings persist for non-integrable models. As a first step, we study the spin-1/2 XXZ chain, where integrability can be broken due to an additional next-nearest neighbor interaction. Furthermore, we analyze the differences of typical and untypical initial states on the basis of their entanglement and their local density of states.

  • Transversality and lattice surgery: exploring realistic routes towards coupled logical qubits with trapped-ion quantum processors.- [PDF] - [Article]

    M. Gutiérrez, M. Müller, A. Bermudez

    Active quantum error correction has been identified as a crucial ingredient of future quantum computers, motivating the recent experimental efforts to encode logical quantum bits using small topological codes. In addition to the demonstration of the beneficial role of the encoding, a break-even point in the progress towards large-scale quantum computers will be the implementation of a universal set of gates. This mid-term challenge will soon be faced by various quantum technologies, which urges the need of realistic assessments of their prospects. In this work, we pursue this goal by assessing the capability of current trapped-ion architectures in facing one of the most demanding parts of this quest: the implementation of an entangling CNOT gate between encoded logical qubits. We present a detailed comparative study of two alternative strategies for trapped-ion topological color codes, either a transversal or a lattice-surgery approach, characterized by a detailed microscopic modeling of both current technological capabilities and experimental sources of noise afflicting the different operations. Our careful fault-tolerant design, together with a low-resource optimization, allows us to determine via exhaustive numerical simulations the experimental regimes where each of the approaches becomes favorable. We hope that our study thereby contributes to guiding the future development of trapped-ion quantum computers.

  • Entanglement entropy in the Long-Range Kitaev chain.- [PDF] - [Article]

    F. Ares, J. G. Esteve, F. Falceto, A. R. de Queiroz

    In this paper we complete the study on the asymptotic behaviour of the entanglement entropy for Kitaev chains with long range pairing. We discover that when the couplings decay with the distance with a critical exponent new properties for the asymptotic growth of the entropy appear. The coefficient of the leading term is not universal any more and the connection with conformal field theories is lost. We perform a numerical and analytical approach to the problem showing a perfect agreement. In order to carry out the analytical study, a new technique for computing the asymptotic behaviour of block Toeplitz determinants with discontinuous symbols has been developed.

  • Dynamics of Entanglement and Uncertainty relation in Coupled Harmonic Oscillator System : Exact Results.- [PDF] - [Article]

    DaeKil Park

    The dynamics of entanglement and uncertainty relation is explored by solving the time-dependent Schr\"{o}dinger equation of the coupled harmonic oscillator system when the angular frequencies and coupling constant are arbitrarily time-dependent. We derive analytically the spectral and Schmidt decompositions for the vacuum solution. Using the decompositions we derive the analytical expressions for von Neumann and R\'{e}nyi entropies. Making use of Wigner function, we derive also the position-momentum uncertainty relations. To show the dynamics of entanglement and uncertainty relation graphically we introduce two toy models and one realistic quenched model. While the dynamics can be conjectured by simple consideration in the toy models, the dynamics in the realistic quenched model is somewhat different from those in the toy models. In particular, the dynamics of entanglement exhibits similar pattern to dynamics of uncertainty parameter in the realistic quenched model.

  • Information Theoretical Analysis of Quantum Metrology.- [PDF] - [Article]

    Yi Peng, Heng Fan

    We establish a direct connection between the recently proposed information theoretic picture of quantum metrology and its conventional root-mean-square-error (RMSE) picture. A complement is conceived of the information-theoretic quantum metrology by showing that any estimation procedure achieves Heisenberg limit in RMSE picture also have the information-theoretic Heisenberg limit for which entangled measurement is not necessary. We explicitly present a Quantum-Classical Parallel strategy of quantum metrology which employs a separable measurement and saturates the Heisenberg limit in both pictures.

  • Mixed Quantum-Classical Electrodynamics: Understanding Spontaneous Decay and Zero Point Energy.- [PDF] - [Article]

    Tao E. Li, Abraham Nitzan, Maxim Sukharev, Todd Martinez, Hsing-Ta Chen, Joseph E. Subotnik

    The dynamics of an electronic two-level system coupled to an electromagnetic field are simulated explicitly for one and three dimensional systems through semiclassical propagation of the Maxwell-Liouville equations. We consider three flavors of mixed quantum-classical dynamics: the classical path approximation (CPA), Ehrenfest dynamics, and symmetrical quantum-classical (SQC) dynamics. The CPA fails to recover a consistent description of spontaneous emission. A consistent "spontaneous" emission can be obtained from Ehrenfest dynamics--provided that one starts in an electronic superposition state. Spontaneous emission is always obtained using SQC dynamics. Using the SQC and Ehrenfest frameworks, we further calculate the dynamics following an incoming pulse, but here we find very different responses: SQC and Ehrenfest dynamics deviate sometimes strongly in the calculated rate of decay of the transient excited state. Nevertheless, our work confirms the earlier observations by W. Miller [J. Chem. Phys. 69, 2188-2195, 1978] that Ehrenfest dynamics can effectively describe some aspects of spontaneous emission and highlights new possibilities for studying light-matter interactions with semiclassical mechanics.

  • Multimode-fiber-based high-dimensional quantum secure communication.- [PDF] - [Article]

    Lyubov V. Amitonova, Tristan B. H. Tentrup, Ivo M. Vellekoop, Pepijn W. H. Pinkse

    Quantum communication aims to provide absolutely secure transmission of secret information. Existing methods encode symbols into single photons or coherent light with much less than one photon on average. Here we propose and demonstrate an original method that is fundamentally secure with weak coherent light even when several photons per symbol are used. Our method does not require a change of measurement basis and works with a high-dimensional alphabet in a simple practical setup. Moreover, it sends information in a deterministic way, allowing direct decoding at the receiver end. This feature makes the method suitable for both quantum key distribution (QKD) as well as quantum secure direct communication (QSDC). The key element of our method is the combination of wavefront shaping with a multimode fiber channel. Since it is based on an optical fiber, our method allows to naturally extend secure communication to larger distances.

  • Combined metallic nano-rings and solid-immersion lenses for bright emission from single InAs/GaAs quantum dots.- [PDF] - [Article]

    Oliver Joe Trojak, Christopher Woodhead, Suk-In Park, Jin Dong Song, Robert James Young, Luca Sapienza

    Solid-state single-photon emitters are key components for integrated quantum photonic devices. However, they can suffer from poor extraction efficiencies, caused by the large refractive index contrast between the bulk material they are embedded in and air: this results in a small fraction (that can be as low as <1%) of the emitted photons reaching free-space collection optics. To overcome this issue, we present a device that combines a metallic nano-ring, positioned on the sample surface and centered around the emitter, and an epoxy-based super-solid immersion lens, deterministically deposited above the ring devices. We show that the combined broadband lensing effect of the nano-ring and of the super-solid immersion lens significantly increases the extraction of light emitted by single InAs/GaAs quantum dots into free space: we observe enhancements in the emitted intensity by the nano-ring of up to a factor 20 and by the super-solid immersion lens of up to a factor 10. Such cumulative enhancements allow us to measure photon fluxes approaching 1 million counts per second, from a single InAs/GaAs quantum dot in bulk. The combined broad-band enhancement in the extraction of light can be implemented with any kind of classical and quantum solid-state emitter and opens the path to the realisation of scalable bright devices. The same approach can also be implemented to improve the absorption of light, for instance for small-area broadband photo-detectors.

  • Enhancement of the photon parametric decay in quasi-two-dimensional subwavelength cavities.- [PDF] - [Article]

    Mikhail Tokman, Zhongqu Long, Sultan AlMutairi, Yongrui Wang, Valery Vdovin, Mikhail Belkin, Alexey Belyanin

    Ultracompact nonlinear optical devices utilizing two-dimensional (2D) semiconductor nanostructures are becoming an integral part of optoelectronic and photonic circuits. Integration of the nonlinear material into a subwavelength cavity or waveguide leads to a strong enhancement of the nonlinear processes and compensates for a small interaction volume. The generic feature of such devices which makes them especially challenging for analysis is strong dissipation of both the nonlinear polarization and highly confined modes of a subwavelength cavity. Here we solve a quantum-electrodynamic problem of the spontaneous and stimulated parametric decay in a nonlinear quasi-2D waveguide or cavity. We develop a rigorous Heisenberg-Langevin approach which includes dissipation and fluctuations in the electron ensemble and in the electromagnetic field of a cavity on equal footing. Our approach does not depend on any particular model of a dissipative reservoir and can be applied to any dissipation mechanism. Moreover, we derive closed-form analytic results for all relevant quantities such as the threshold for parametric instability and the parametric signal power. We find a strong reduction in the parametric instability threshold for quantum wells and other 2D nonlinear materials in a subwavelength cavity.

  • Precisely controlling the reflection phase of a photon via a strongly-coupled ancilla dressed qubit.- [PDF] - [Article]

    Felix Motzoi, Klaus Mølmer

    We propose that Rydberg dressing of a single qubit atom can be used to control a surrounding ensemble of three-level atoms and hereby the phase of light reflected by an optical cavity. Our scheme employs an ensemble dark resonance that is perturbed by the qubit state of a single atom to yield a single-atom single-photon gate. We show here that off-resonant Rydberg dressing of the qubit offers experimentally-viable regimes of operation that drastically reduce error compared to schemes using shelved Rydberg population. Such low errors (in the $10^{-3}$ range) are a necessary condition for fault-tolerant optical-photon, gate-based quantum computation. We also demonstrate the technique for microwave circuit-QED, where a strongly-coupled ancilla superconducting qubit can be used in the place of the atomic ensemble to provide high-fidelity coupling to microwave photons.

  • Lifting randomized query complexity to randomized communication complexity.- [PDF] - [Article] - [UPDATED]

    Anurag Anshu, Naresh B. Goud, Rahul Jain, Srijita Kundu, Priyanka Mukhopadhyay

    We show that for a relation $f\subseteq \{0,1\}^n\times \mathcal{O}$ and a function $g:\{0,1\}^{m}\times \{0,1\}^{m} \rightarrow \{0,1\}$ (with $m= O(\log n)$), $$\mathrm{R}_{1/3}(f\circ g^n) = \Omega\left(\mathrm{R}_{1/3}(f) \cdot \left(\log\frac{1}{\mathrm{disc}(M_g)} - O(\log n)\right)\right),$$ where $f\circ g^n$ represents the composition of $f$ and $g^n$, $M_g$ is the sign matrix for $g$, $\mathrm{disc}(M_g)$ is the discrepancy of $M_g$ under the uniform distribution and $\mathrm{R}_{1/3}(f)$ ($\mathrm{R}_{1/3}(f\circ g^n)$) denotes the randomized query complexity of $f$ (randomized communication complexity of $f\circ g^n$) with worst case error $\frac{1}{3}$. In particular, this implies that for a relation $f\subseteq \{0,1\}^n\times \mathcal{O}$, $$\mathrm{R}_{1/3}(f\circ \mathrm{IP}_m^n) = \Omega\left(\mathrm{R}_{1/3}(f) \cdot m\right),$$ where $\mathrm{IP}_m:\{0,1\}^m\times \{0,1\}^m\rightarrow \{0,1\}$ is the Inner Product (modulo $2$) function and $m= O(\log(n))$.

  • Simulating Open Quantum Systems with Hamiltonian Ensembles and the Nonclassicality of the Dynamics.- [PDF] - [Article] - [UPDATED]

    Hong-Bin Chen, Clemens Gneiting, Ping-Yuan Lo, Yueh-Nan Chen, Franco Nori

    The incoherent dynamical properties of open quantum systems are generically attributed to an ongoing correlation between the system and its environment. Here, we propose a novel way to assess the nature of these system-environment correlations by examining the system dynamics alone. Our approach is based on the possibility or impossibility to simulate open-system dynamics with Hamiltonian ensembles. As we show, such (im)possibility to simulate is closely linked to the system-environment correlations. We thus define the nonclassicality of open-system dynamics in terms of the nonexistence of a Hamiltonian-ensemble simulation. This classifies any nonunital open-system dynamics as nonclassical. We give examples for open-system dynamics that are unital and classical, as well as unital and nonclassical.

  • High-Fidelity Preservation of Quantum Information During Trapped-Ion Transport.- [PDF] - [Article] - [UPDATED]

    Peter Kaufmann, Timm F. Gloger, Delia Kaufmann, Michael Johanning, Christof Wunderlich

    A promising scheme for building scalable quantum simulators and computers is the synthesis of a scalable system using interconnected subsystems. A prerequisite for this approach is the ability to faithfully transfer quantum information between subsystems. With trapped atomic ions, this can be realized by transporting ions with quantum information encoded into their internal states. Here, we measure with high precision the fidelity of quantum information encoded into hyperfine states of a 171Yb+ ion during ion transport in a microstructured Paul trap. Ramsey spectroscopy of the ion's internal state is interleaved with up to 4000 transport operations over a distance of 280 {\mu}m each taking 12.8 {\mu}s. We obtain a state fidelity of 99.9994(+6/-7)per ion transport.

  • Long-range big quantum-data transmission.- [PDF] - [Article] - [UPDATED]

    M. Zwerger, A. Pirker, V. Dunjko, H. J. Briegel, W. Dür

    We introduce an alternative type of quantum repeater for long-range quantum communication with improved scaling with the distance. We show that by employing hashing, a deterministic entanglement distillation protocol with one-way communication, one obtains a scalable scheme that allows one to reach arbitrary distances, with constant overhead in resources per repeater station, and ultrahigh rates. In practical terms, we show that also with moderate resources of a few hundred qubits at each repeater station, one can reach intercontinental distances. At the same time, a measurement-based implementation allows one to tolerate high loss, but also operational and memory errors of the order of several percent per qubit. This opens the way for long-distance communication of big quantum data.

  • Derivation of the statistics of quantum measurements from the action of unitary dynamics.- [PDF] - [Article] - [UPDATED]

    Keito Hibino, Kazuya Fujiwara, Jun-Yi Wu, Masataka Iinuma, Holger F. Hofmann

    Quantum statistics is defined by Hilbert space products between the eigenstates associated with state preparation and measurement. The same Hilbert space products also describe the dynamics generated by a Hamiltonian when one of the states is an eigenstate of energy E and the other represents an observable B. In this paper, we investigate this relation between the observable time evolution of quantum systems and the coherence of Hilbert space products in detail. It is shown that the times of arrival for a specific value of B observed with states that have finite energy uncertainties can be used to derive the Hilbert space product between eigenstates of energy E and eigenstates of the dynamical variable B. In these Hilbert space products, quantum phases and interference effects appear in the form of an action that relates energy to time in the experimentally observable dynamics of localized states. Quantum effects emerge in the measurement statistics when the precise control of energy in quantum state preparation results in a coherent randomization of the dynamics, such that two different arrival times contribute to the quantum statistics of the same measurement outcome B. The non-classical features associated with quantum interference can thus be explained as a consequence of quantum dynamics and its role in state preparation and measurement, indicating that the apparent randomness of control described by the energy-time uncertainties is not merely a technical problem but rather originates from the fundamental nature of interactions between physical systems.

  • Cooperative Effects in Closely Packed Quantum Emitters with Collective Dephasing.- [PDF] - [Article] - [UPDATED]

    B. Prasanna Venkatesh, M. L. Juan, O. Romero-Isart

    In a closely packed ensemble of quantum emitters, cooperative effects are typically suppressed due to the dephasing induced by the dipole-dipole interactions. Here, we show that by adding sufficiently strong collective dephasing cooperative effects can be restored. In particular, we show that the dipole force on a closely packed ensemble of strongly driven two-level quantum emitters, which collectively dephase, is enhanced in comparison to the dipole force on an independent non-interacting ensemble. Our results are relevant to solid state systems with embedded quantum emitters such as colour centers in diamond and superconducting qubits in microwave cavities and waveguides.

  • An Atom Interferometer inside a Hollow-core Photonic Crystal Fiber.- [PDF] - [Article] - [UPDATED]

    Mingjie Xin, Wui Seng Leong, Zilong Chen, Shau-Yu Lan

    Coherent interactions between electromagnetic and matter waves lie at the heart of quantum science and technology. However, the diffraction nature of light has limited the scalability of many atom-light based quantum systems. Here, we use the optical fields in a hollow-core photonic crystal fiber to spatially split, reflect, and recombine a coherent superposition state of free-falling 85Rb atoms to realize an inertia-sensitive atom interferometer. The interferometer operates over a diffraction-free distance, and the contrasts and phase shifts at different distances agree within one standard error. The integration of phase coherent photonic and quantum systems here shows great promise to advance the capability of atom interferometers in the field of precision measurement and quantum sensing with miniature design of apparatus and high efficiency of laser power consumption.

  • Essentiality of Entanglement in a Quantum Algorithm.- [PDF] - [Article] - [UPDATED]

    Ashutosh K. Goswami, Prasanta K. Panigrahi

    Quantum algorithms could efficiently solve certain classically intractable problems by exploiting quantum parallelism. To date, whether the quantum entanglement is useful or not for quantum computing is still a question of debate. Here, we present a new quantum algorithm to show that entanglement could help to gain advantage over classical algorithm and even the quantum algorithm without entanglement. Furthermore, we implement experiments to demonstrate our proposed algorithm using superconducting qubits. Our results show the viability of the algorithm and suggest that entanglement is essential in getting quantum speedup for certain problems in quantum computing, which provide a reliable and clear guidance for developing useful quantum algorithms in future.

  • Fracton topological phases from strongly coupled spin chains.- [PDF] - [Article] - [UPDATED]

    Gábor B. Halász, Timothy H. Hsieh, Leon Balents

    We provide a new perspective on fracton topological phases, a class of three-dimensional topologically ordered phases with unconventional fractionalized excitations that are either completely immobile or only mobile along particular lines or planes. We demonstrate that a wide range of these fracton phases can be constructed by strongly coupling mutually intersecting spin chains and explain via a concrete example how such a coupled-spin-chain construction illuminates the generic properties of a fracton phase. In particular, we describe a systematic translation from each coupled-spin-chain construction into a parton construction where the partons correspond to the excitations that are mobile along lines. Remarkably, our construction of fracton phases is inherently based on spin models involving only two-spin interactions and thus brings us closer to their experimental realization.

  • Entanglement verification protocols for distributed systems based on the Quantum Recursive Network Architecture.- [PDF] - [Article] - [UPDATED]

    Michele Amoretti, Stefano Carretta

    In distributed systems based on the Quantum Recursive Network Architecture, quantum channels and quantum memories are used to establish entangled quantum states between node pairs. Such systems are robust against attackers that interact with the quantum channels. Conversely, weaknesses emerge when an attacker takes full control of a node and alters the configuration of the local quantum memory, either to make a denial-of-service attack or to reprogram the node. In such a scenario, entanglement verification over quantum memories is a means for detecting the intruder. Usually, entanglement verification approaches focus either on untrusted sources of entangled qubits (photons, in most cases) or on eavesdroppers that interfere with the quantum channel while entangled qubits are transmitted. Instead, in this work we assume that the source of entanglement is trusted, but parties may be dishonest. Looking for efficient entanglement verification protocols that only require classical channels and local quantum operations to work, we thoroughly analyze the one proposed by Nagy and Akl, that we denote as NA2010 for simplicity, and we define and analyze two entanglement verification protocols based on teleportation (denoted as AC1 and AC2), characterized by increasing efficiency in terms of intrusion detection probability versus sacrificed quantum resources.

  • Topological characterization of chiral models through their long time dynamics.- [PDF] - [Article] - [UPDATED]

    Maria Maffei, Alexandre Dauphin, Filippo Cardano, Maciej Lewenstein, Pietro Massignan

    We study chiral models in one spatial dimension, both static and periodically driven. We demonstrate that their topological properties may be read out through the long time limit of a bulk observable, the mean chiral displacement. The derivation of this result is done in terms of spectral projectors, allowing for a detailed understanding of the physics. We show that the proposed detection converges rapidly and it can be implemented in a wide class of chiral systems. Furthermore, it can measure arbitrary winding numbers and topological boundaries, it applies to all non-interacting systems, independently of their quantum statistics, and it requires no additional elements, such as external fields, nor filled bands.

  • Bounding the energy-constrained quantum and private capacities of phase-insensitive Gaussian channels.- [PDF] - [Article] - [UPDATED]

    Kunal Sharma, Mark M. Wilde, Sushovit Adhikari, Masahiro Takeoka

    We establish several upper bounds on the energy-constrained quantum and private capacities of all phase-insensitive Gaussian channels. The first upper bound, which we call the "data-processing bound," is the simplest and is obtained by decomposing a phase-insensitive channel as a pure-loss channel followed by a quantum-limited amplifier channel. We prove that the data-processing bound can be at most 1.45 bits larger than a known lower bound on these capacities of the phase-insensitive Gaussian channel. The other two upper bounds, which we call the ``$\varepsilon$-degradable bound'' and the ``$\varepsilon$-close-degradable bound,'' are established using the notion of approximate degradability along with energy constraints. We find a strong limitation on any potential superadditivity of the coherent information of any phase-insensitive Gaussian channel in the low-noise regime, as the data-processing bound is very near to a known lower bound in such cases. We also find improved achievable rates of private communication through bosonic thermal channels, by employing coding schemes that make use of displaced thermal states. We end by proving that an optimal Gaussian input state for the energy-constrained, generalized channel divergence of two particular Gaussian channels is the two-mode squeezed vacuum state that saturates the energy constraint. What remains open for several interesting channel divergences, such as the diamond norm or the R\'enyi channel divergence, is to determine whether, among all input states, a Gaussian state is optimal.

  • Dissipative Phase Transition in the Open Quantum Rabi Model.- [PDF] - [Article] - [UPDATED]

    Myung-Joong Hwang, Peter Rabl, Martin B. Plenio

    We demonstrate that the open quantum Rabi model (QRM) exhibits a second-order dissipative phase transition (DPT) and propose a method to observe this transition with trapped ions. The interplay between the ultrastrong qubit-oscillator coupling and the oscillator damping brings the system into a steady-state with a diverging number of excitations, in which a DPT is allowed to occur even with a finite number of system components. The universality class of the open QRM, modified from the closed QRM by a Markovian bath, is identified by finding critical exponents and scaling functions using the Keldysh functional integral approach. We propose to realize the open QRM with two trapped ions where the coherent coupling and the rate of dissipation can be individually controlled and adjusted over a wide range. Thanks to this controllability, our work opens a possibility to investigate potentially rich dynamics associated with a dissipative phase transition.

  • Ultimate entanglement robustness of two-qubit states against general local noises.- [PDF] - [Article] - [UPDATED]

    Sergey N. Filippov, Vladimir V. Frizen, Daria V. Kolobova

    We study the problem of optimal preparation of a bipartite entangled state, which remains entangled the longest time under action of local qubit noises. We show that for unital noises such a state is always maximally entangled, whereas for nonunital noises, it is not. We develop a decomposition technique relating nonunital and unital qubit channels, based on which we find the explicit form of the ultimately robust state for general local noises. We illustrate our findings by amplitude damping processes at finite temperature, for which the ultimately robust state remains entangled up to two times longer than conventional maximally entangled states.

  • Charge response of the Majorana toric code.- [PDF] - [Article] - [UPDATED]

    Ananda Roy, Fabian Hassler

    At zero temperature, a two dimensional lattice of Majorana zero modes on mesoscopic superconducting islands has a topologically ordered toric code phase. Recently, a Landau field theory has been proposed for the system that captures its different phases and the associated phase-transitions. It was shown that with the increase of Josephson tunneling between the islands, a continuous symmetry-breaking 3D-XY transition gets transformed into a discrete symmetry-breaking 3D-Ising transition through a couple of tricritical points and first order transitions. Using the proposed field theory, we analyze the charge-response of the system at the different continuous phase-transitions. We calculate the universal conductivity at the 3D-XY transitions and the change in the superconducting density at the Ising transition using 1/N expansion. Furthermore, by computing a one-loop correction to the field theory, we show that an additional tricritical point is likely to be present in the phase-diagram. Finally, we provide a mean-field calculation that supports the earlier proposed field theory.

  • Quantum chaos of dark matter in the Solar System.- [PDF] - [Article] - [UPDATED]


    We perform time-dependent analysis of quantum dynamics of dark matter particles in the Solar System. It is shown that this problem has similarities with a microwave ionization of Rydberg atoms studied previously experimentally and analytically. On this basis it is shown that the quantum effects for chaotic dark matter dynamics become significant for dark matter mass ratio to electron mass being smaller than $2 \times 10^{-15}$. Below this border multiphoton diffusion over Rydberg states of dark matter atom becomes exponentially localized in analogy with the Anderson localization in disordered solids. The life time of dark matter in the Solar System is determined in dependence on mass ratio in the localized phase and a few photon ionization regime. The quantum effects for dark matter captured by other binary systems are also discussed.

  • Zero energy mode for a spin-1/2 charge particle in a two-dimensional magnetic field with the constant asymptotics.- [PDF] - [Article] - [UPDATED]

    Juan Sebastian Ardenghi, Lucas Sourrouille

    We study the influence of a two-dimensional transversal magnetic field with the asymptotics $B(r\to \infty)= B_0$ in a spin 1/2 charge particle. It is shown that the zero-energy solutions can exist only for one spin direction, depending on the sign of the magnetic field in the infinite boundary. This, shows that zero-energy level is robust with respect to possible inhomogeneities of the magnetic field. In addition, we show that the number of the states with zero energy for one spin projection is infinity.

  • X-Cube Fracton Model on Generic Lattices: Phases and Geometric Order.- [PDF] - [Article] - [UPDATED]

    Kevin Slagle, Yong Baek Kim

    Fracton order is a new kind of quantum order characterized by topological excitations which exhibit remarkable mobility restrictions and a robust ground state degeneracy (GSD) which can increase exponentially with system size. In this manuscript, we present a generic lattice construction (in three dimensions) for a generalized X-cube model of fracton order, where the mobility restrictions of the subdimensional particles inherit the geometry of the lattice. This helps explain a previous result that lattice curvature can produce a robust GSD, even on a manifold with trivial topology. We provide explicit examples to show that the (zero temperature) phase of matter is sensitive to the lattice geometry. In one example, the lattice geometry confines the dimension-1 particles to small loops, which allows the fractons to be fully mobile charges, and the resulting phase is equivalent to 3+1D toric code. However, the phase is sensitive to more than just lattice curvature; different lattices without curvature (e.g. cubic or stacked kagome lattices) also result in different phases of matter, which are separated by phase transitions. Unintuitively however, according to a previous definition of phase [Chen, Gu, Wen 2010], even just a rotated or rescaled cubic results in different phases of matter, which motivates us to propose a new and coarser definition of phase for gapped ground states and fracton topological order. The new equivalence relation between ground states is given by the composition of a local unitary transformation and a quasi-isometry (which can rotate and rescale the lattice); equivalently, ground states are in the same phase if they can be adiabatically connected by varying both the Hamiltonian and the positions of the degrees of freedom (via a quasi-isometry).In light of the importance of geometry, we further propose that fracton orders should be regarded as a geometric order.

  • Synthesis of antisymmetric spin exchange interaction and entanglement generation with chiral spin states in a superconducting circuit.- [PDF] - [Article] - [UPDATED]

    Da-Wei Wang, Chao Song, Wei Feng, Han Cai, Da Xu, Hui Deng, Dongning Zheng, Xiaobo Zhu, H. Wang, Shiyao Zhu, Marlan O. Scully

    We have synthesized the anti-symmetric spin exchange interaction (ASI), which is also called the Dzyaloshinskii-Moriya interaction, in a superconducting circuit containing five superconducting qubits connected to a bus resonator, by periodically modulating the transition frequencies of the qubits with different modulation phases. This allows us to show the chiral spin dynamics in three-, four- and five-spin clusters. We also demonstrate a three-spin chiral logic gate and entangle up to five qubits in Greenberger-Horne-Zeilinger states. Our results pave the way for quantum simulation of magnetism with ASI and quantum computation with chiral spin states.

  • Simulation of low-depth quantum circuits as complex undirected graphical models.- [PDF] - [Article] - [UPDATED]

    Sergio Boixo, Sergei V. Isakov, Vadim N. Smelyanskiy, Hartmut Neven

    Near term quantum computers with a high quantity (around 50) and quality (around 0.995 fidelity for two-qubit gates) of qubits will approximately sample from certain probability distributions beyond the capabilities of known classical algorithms on state-of-the-art computers, achieving the first milestone of so-called quantum supremacy. This has stimulated recent progress in classical algorithms to simulate quantum circuits. Classical simulations are also necessary to approximate the fidelity of multiqubit quantum computers using cross entropy benchmarking. Here we present numerical results of a classical simulation algorithm to sample universal random circuits, on a single workstation, with more qubits and depth than previously reported. For example, circuits with $5 \times 9$ qubits of depth 37, $7 \times 8$ qubits of depth 27, and $10 \times (\kappa > 10)$) qubits of depth 19 are all easy to sample. We also show up to what depth the sampling, or estimation of observables, is trivially parallelizable. The algorithm is related to the "Feynmann path" method to simulate quantum circuits. For low-depth circuits, the algorithm scales exponentially in the depth times the smaller lateral dimension, or the treewidth, as explained in Boixo et. al., and therefore confirms the bounds in that paper. In particular, circuits with $7 \times 7$ qubits and depth 40 remain currently out of reach. Follow up work on a supercomputer environment will tighten this bound.

  • Higher-Order Interactions in Quantum Optomechanics: Application of Operator Method.- [PDF] - [Article] - [UPDATED]

    Georg Arnold, Sina Khorasani

    We demonstrate the application of higher-order operator bases to the solution of standard optomechanics. It has been shown that there exists higher-order effects at high intracavity photon occupations, including inequivalency of red and blue side-band frequencies. Similarly, a higher-order resonance shift exists which primarily appears as changes in the optical resonance frequency, while the mechanical frequency should also be affected. As a result of optomechanical interactions with the zero-point field, the mechanical frequency undergoes a temperature-dependent shift even in the absence of external optical drive, which can be analyzed using the introduced method. We also have calculated corrections to the optomechanical spring effect due to higher-order interactions, and shown that these corrections can be quite important at low cavity photon numbers. This has been verified experimentally and we are able to show a reasonably good fit to a set of measurements. It is shown that there exists non-unique and various choices for the higher-order operators to solve the optomechanical interaction with different multiplicative noise terms, among which a minimal basis with higher-order operators offers exactly linear Langevin equations. Furthermore, the use of minimal basis fully decouples one of the Langevin equations, leaving the whole standard optomechanical problem exactly solvable by explicit expressions. Similar approach can be used outside the domain of standard optomechanics to quadratic and all other types of nonlinear interactions in quantum physics.

  • How does parity-time symmetry break? -- pseudo-Hermiticity and resonance between positive- and negative-action modes.- [PDF] - [Article] - [UPDATED]

    Ruili Zhang, Hong Qin, Jianyuan Xiao, Jian Liu

    It is generally believed that Parity-Time (PT)-symmetry breaks at exceptional points (EPs) where eigenvalues coincide. However, we prove that eigenvalue coalescence is a necessary but not sufficient condition for PT-symmetry breaking, and that coalescence of both eigenvalues and eigenvectors is a sufficient but not necessary condition. Instead, we show that PT-symmetry breaks at EPs when and only when a positive-action mode resonates with a negative-action mode. This is accomplished by proving a remarkable fact that in finite dimensions, a PT-symmetric Hamiltonian is necessarily pseduo-Hermitian, regardless whether it is diagonalizable or not.

  • Non-Locality distillation in tripartite NLBs.- [PDF] - [Article] - [UPDATED]

    Talha Lateef

    In quantum mechanics some spatially separated sub-systems behave as if they are part of a single system, the superposition of states of this single system cannot be written as products of states of individual sub-systems,we say that the state of such system is entangled, such systems give rise to non-local correlations between outcomes of measurements. The non-local correlations are conditional probability distributions of some measurement outcomes given some measurement settings and cannot be explained by shared information.These correlations can be studied using a non-local box(NLB) which can be viewed as a quantum systema. A NLB is an abstract object which has number of inputs(measurement settings) and number of outputs(outcomes), such NLBs can be both quantum and super-quantum. The correlations are of use in quantum information theory, the stronger the correlations the more useful they are, hence we study protocols that have multiple weaker non-local systems, application of these protocols to weaker systems may result in stronger non-local correlations, we call such protocols non-locality distillation protocols. In our work here we present non-locality distillation protocols for tripartite NLBs specifically GHZ box and class 44,45 and 46 of no-signalling polytope.

  • Additivity of entropic uncertainty relations.- [PDF] - [Article] - [UPDATED]

    Rene Schwonnek

    We consider the uncertainty between two pairs of local projective measurements performed on a multipartite system. We show that the optimal bound in any linear uncertainty relation, formulated in terms of the Shannon entropy, is additive. This directly implies, against naive intuition, that the minimal entropic uncertainty can always be realized by fully separable states. Hence, in contradiction to proposals by other authors, no entanglement witness can be constructed solely by comparing the attainable uncertainties of entangled and separable states. However, our result gives rise to a huge simplification for computing global uncertainty bounds as they now can be deduced from local ones. Furthermore, we provide the natural generalization of the Maassen and Uffink inequality for linear uncertainty relations with arbitrary positive coefficients.

  • Coupling Two Spin Qubits with a High-Impedance Resonator.- [PDF] - [Article] - [UPDATED]

    S.P. Harvey, C.G.L. Bøttcher, L.A. Orona, S.D. Bartlett, A.C. Doherty, A. Yacoby

    Fast, high-fidelity single and two-qubit gates are essential to building a viable quantum information processor, but achieving both in the same system has proved challenging for spin qubits. We propose and analyze an approach to perform a long-distance two-qubit controlled phase (CPHASE) gate between two singlet-triplet qubits using an electromagnetic resonator to mediate their interaction. The qubits couple longitudinally to the resonator, and by driving the qubits near the resonator's frequency they can be made to acquire a state-dependent geometric phase that leads to a CPHASE gate independent of the initial state of the resonator. Using high impedance resonators enables gate times of order 10 ns while maintaining long coherence times. Simulations show average gate fidelities of over 96% using currently achievable experimental parameters and over 99% using state-of-the-art resonator technology. After optimizing the gate fidelity in terms of parameters tuneable in-situ, we find it takes a simple power-law form in terms of the resonator's impedance and quality and the qubits' noise bath.

  • Information is not a thermodynamic resource.- [PDF] - [Article] - [UPDATED]

    Robert Alicki

    The so-called information-thermodynamics link has been created in a series of works starting from Maxwell demon and established by the idea of transforming information into work in the though experiment of Szilard which then evolved into the vast field of research. The aim of this note is firstly to present two new models of the Szilard engine containing arbitrary number of molecules which show irrelevance of acquiring information for work extraction. Secondly, the difference between the definition of entropy for ergodic systems and systems with ergodicity breaking constraints is emphasized. The role of nonergodic systems as information carriers and the thermodynamic cost of stability and accuracy of information encoding and processing is briefly discussed.


  • Measurement of the the liquid argon energy response to nuclear and electronic recoils.- [PDF] - [Article]

    P. Agnes, J. Dawson, S. De Cecco, A. Fan, G. Fiorillo, D. Franco, C. Galbiati, C. Giganti, T. N. Johnson, G. Korga, D. Kryn, M. Lebois, A. Mandarano, C. J. Martoff, A. Navrer-Agasson, E. Pantic, L. Qi, A. Razeto, A. L. Renshaw, Q. Riffard, B. Rossi, C. Savarese, B. Schlitzer, A. Tonazzo, H. Wang, Y. Wang, A. W. Watson, J. N. Wilson

    A liquid argon time projection chamber, constructed for the Argon Response to Ionization and Scintillation (ARIS) experiment, has been exposed to the highly collimated and quasi-monoenergetic LICORNE neutron beam at the Institute de Physique Nuclaire Orsay in order to study the scintillation response to nuclear and electronic recoils. An array of liquid scintillator detectors, arranged around the apparatus, tag scattered neutrons and select nuclear recoil energies in the [7, 120] keV energy range. The relative scintillation efficiency of nuclear recoils was measured to high precision at null field, and the ion-electron recombination probability was extracted for a range of applied electric fields. Single Compton scattered electrons, produced by gammas emitted from the de-excitation of $^7$Li* in coincidence with the beam pulse, along with calibration gamma sources, are used to extract the recombination probability as a function of energy and electron drift field. The ARIS results have been compared with three recombination probability parameterizations (Thomas-Imel, Doke-Birks, and PARIS), allowing for the definition of a fully comprehensive model of the liquid argon response to nuclear and electronic recoils in the energy range of interest for dark matter searches.

  • A search for high-mass resonances decaying to $\tau\nu$ in $pp$ collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector.- [PDF] - [Article]

    ATLAS Collaboration

    A search for high-mass resonances decaying to $\tau\nu$ using proton-proton collisions at $\sqrt{s}$ = 13 TeV produced by the Large Hadron Collider is presented. Only $\tau$-lepton decays with hadrons in the final state are considered. The data were recorded with the ATLAS detector and correspond to an integrated luminosity of 36.1 fb$^{-1}$. No statistically significant excess above the Standard Model expectation is observed; model-independent upper limits are set on the visible $\tau\nu$ production cross section. Heavy $W^{\prime}$ bosons with masses less than 3.7 TeV in the Sequential Standard Model and masses less than 2.2-3.8 TeV depending on the coupling in the non-universal G(221) model are excluded at the 95% credibility level.

  • Neutral pion and $\eta$ meson production in p-Pb collisions at $\mathbf{\sqrt{s_{\rm NN}}} = 5.02$ TeV.- [PDF] - [Article]

    ALICE Collaboration

    Neutral pion and $\eta$ meson invariant differential yields were measured in non-single diffractive p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV with the ALICE experiment at the CERN LHC. The analysis combines results from three complementary photon measurements, utilizing the PHOS and EMCal calorimeters and the Photon Conversion Method. The invariant differential yields of $\pi^0$ and $\eta$ meson inclusive production are measured near mid-rapidity in a broad transverse momentum range of $0.3<p_{\rm T}< 20$ GeV/$c$ and $0.7<p_{\rm T}<20$ GeV/$c$, respectively. The measured $\eta$/$\pi^{0}$ ratio increases with $p_{\rm T}$ and saturates for $p_{\rm T} > 4$ GeV/$c$ at $0.483\pm 0.015_{\rm stat}\pm 0.015_{\rm sys}$. A deviation from $m_{\rm T}$ scaling is observed for $p_{\rm T}<2$ GeV/$c$. The measured $\eta$/$\pi^{0}$ ratio is consistent with previous measurements from proton-nucleus and pp collisions over the full $p_{\rm T}$ range. The measured $\eta$/$\pi^{0}$ ratio at high $p_{\rm T}$ also agrees within uncertainties with measurements from nucleus-nucleus collisions. The $\pi^0$ and $\eta$ yields in p-Pb relative to the scaled pp interpolated reference, $R_{\rm pPb}$, are presented for $0.3<p_{\rm T}<20$ GeV/$c$ and $0.7<p_{\rm T}< 20$ GeV/$c$, respectively. The results are compared with theoretical model calculations. The values of $R_{\rm pPb}$ are consistent with unity for transverse momenta above 2 GeV/$c$. These results support the interpretation that the suppressed yield of neutral mesons measured in Pb-Pb collisions at LHC energies is due to parton energy loss in the hot QCD medium.

  • Relativistic effects in ab-initio electron-nucleus scattering.- [PDF] - [Article]

    Noemi Rocco, Winfried Leidemann, Alessandro Lovato, Giuseppina Orlandini

    The electromagnetic responses obtained from Green's function Monte Carlo (GFMC) calculations are based on realistic treatments of nuclear interactions and currents. The main limitations of this method comes from its nonrelativistic nature and its computational cost, the latter hampering the direct evaluation of the inclusive cross sections as measured by experiments. We extend the applicability of GFMC in the quasielastic region to intermediate momentum transfers by performing the calculations in a reference frame that minimizes nucleon momenta. Additional relativistic effects in the kinematics are accounted for employing the two-fragment model. In addition, we developed a novel algorithm, based on the concept of first-kind scaling, to compute the inclusive electromagnetic cross section of $^4$He through an accurate and reliable interpolation of the response functions. A very good agreement is obtained between theoretical and experimental cross sections for a variety of kinematical setups. This offers a promising prospect for the data analysis of neutrino-oscillation experiments that requires an accurate description of nuclear dynamics in which relativistic effects are fully accounted for.

  • ROPPERI - A TPC readout with GEMs, pads and Timepix.- [PDF] - [Article]

    Ulrich Einhaus, Jochen Kaminksi, Michele Caselle

    The concept of a hybrid readout of a time projection chamber is presented. It combines a GEM-based amplification and a pad-based anode plane with a pixel chip as readout electronics. This way, a high granularity enabling to identify electron clusters from the primary ionisation is achieved as well as flexibility and large anode coverage. The benefits of this high granularity, in particular for dE/dx measurements, are outlined and results of a simulation-based performance study are given. The structure of the first prototype board is discussed, including adaptions based on a very preliminary first measurement for a second production towards a proof-of-principle.

  • Improved tuning methods for Monte Carlo generators.- [PDF] - [Article]

    Fabian Klimpel

    The Monte Carlo event generators (MC) are used for the simulation of different processes in high energy physics. To achieve the best description of the data, the parameters of simulations are adjusted (tuned) with different methods. In this thesis extensions of the Professor MC tuning system were developed and tested. The extensions improve the optimization algorithm for the search of the MC parameters that provide the best description of data. The first extension enables a Bayesian approach in the optimization procedure and the second implements a new adaptive interpolation algorithm for a search of the optimum in the MC parameter space. The performance of the developed extensions was studied with a tuning of the Pythia8 MC event generator and visible improvements in the stability of the results were found in comparison to the results delivered by the standard approach.

  • Search for dark matter and unparticles in events with a Z boson and missing transverse momentum in proton-proton collisions at sqrt(s) = 13 TeV.- [PDF] - [Article] - [UPDATED]

    CMS Collaboration

    A search for dark matter and unparticle production at the LHC has been performed using events containing two charged leptons (electrons or muons), consistent with the decay of a Z boson, and large missing transverse momentum. This study is based on data collected with the CMS detector in 2015, corresponding to an integrated luminosity of 2.3 inverse femtobarns of proton-proton collisions at the LHC, at a center-of-mass energy of 13 TeV. No excess over the standard model expectation is observed. Compared to previous searches in this topology, which exclusively relied on effective field theories, the results are interpreted in terms of a simplified model of dark matter production for both vector and axial vector couplings between a mediator and dark matter particles. The first study of this class of models using CMS data at sqrt(s) = 13 TeV is presented. Additionally, effective field theories of dark matter and unparticle production are used to interpret the data.

  • Determination of the strong coupling constant $\alpha_s$ from transverse energy-energy correlations in multijet events at $\sqrt{s} = 8$ TeV using the ATLAS detector.- [PDF] - [Article] - [UPDATED]

    ATLAS Collaboration

    Measurements of transverse energy-energy correlations and their associated asymmetries in multi-jet events using the ATLAS detector at the LHC are presented. The data used correspond to $\sqrt{s} = 8$ TeV proton-proton collisions with an integrated luminosity of 20.2 fb$^{-1}$. The results are presented in bins of the scalar sum of the transverse momenta of the two leading jets, unfolded to the particle level and compared to the predictions from Monte Carlo simulations. A comparison with next-to-leading-order perturbative QCD is also performed, showing excellent agreement within the uncertainties. From this comparison, the value of the strong coupling constant is extracted for different energy regimes, thus testing the running of $\alpha_s(\mu)$ predicted in QCD up to scales over 1 TeV. A global fit to the transverse energy-energy correlation distributions yields $\alpha_s(m_Z) = 0.1162 \pm 0.0011 \mbox{ (exp.)}^{+0.0084}_{-0.0070} \mbox{ (theo.)}$, while a global fit to the asymmetry distributions yields a value of $\alpha_s(m_Z) = 0.1196 \pm 0.0013 \mbox{ (exp.)}^{+0.0075}_{-0.0045} \mbox{ (theo.)}$.

  • The STAR MAPS-based PiXeL detector.- [PDF] - [Article] - [UPDATED]

    Giacomo Contin, Leo Greiner, Joachim Schambach, Michal Szelezniak, Eric Anderssen, Jacque Bell, Mario Cepeda, Thomas Johnson, Hao Qiu, Hans-Georg Ritter, Joseph Silber, Thorsten Stezelberger, Xiangming Sun, Co Tran, Chinh Vu, Howard Wieman, Kenneth Wilson, Rhonda Witharm, Samuel Woodmansee, John Wolf

    The PiXeL detector (PXL) for the Heavy Flavor Tracker (HFT) of the STAR experiment at RHIC is the first application of the state-of-the-art thin Monolithic Active Pixel Sensors (MAPS) technology in a collider environment. Custom built pixel sensors, their readout electronics and the detector mechanical structure are described in detail. Selected detector design aspects and production steps are presented. The detector operations during the three years of data taking (2014-2016) and the overall performance exceeding the design specifications are discussed in the conclusive sections of this paper.


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