RAS_WEB (Page 2,335)

Optimisation based algorithm for finding the action of cosmological phase transitions. (arXiv:2103.01985v2 [astro-ph.CO] UPDATED) <a href="http://arxiv.org/find/astro-ph/1/au:+Bardsley_M/0/1/0/all/0/1">Michael Bardsley</a> We present the OptiBounce algorithm, a new and fast method for finding the bounce action for cosmological phase transitions. This is done by direct solution of the “reduced” minimisation problem proposed by Coleman, Glaser, and Martin. By using a new formula for the action, our method avoids the rescaling step used in other algorithms based on this formulation. The bounce path is represented using a pseudo-spectral Gauss-Legendre collocation scheme leading to a non-linear optimisation problem over the collocation coefficients. Efficient solution of this problem is enabled by recentRead More →

Field linkage and magnetic helicity density. (arXiv:2102.11238v2 [astro-ph.SR] UPDATED) <a href="http://arxiv.org/find/astro-ph/1/au:+Lund_K/0/1/0/all/0/1">K. Lund</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Jardine_M/0/1/0/all/0/1">M. Jardine</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Russell_A/0/1/0/all/0/1">A. J. B. Russell</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Donati_J/0/1/0/all/0/1">J.-F. Donati</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fares_R/0/1/0/all/0/1">R. Fares</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Folsom_C/0/1/0/all/0/1">C. P. Folsom</a> The helicity of a magnetic field is a fundamental property that is conserved in ideal MHD. It can be explored in the stellar context by mapping large-scale magnetic fields across stellar surfaces using Zeeman-Doppler imaging. A recent study of 51 stars in the mass range 0.1-1.34 M$_odot$ showed that the photospheric magnetic helicity density follows a single power law when plotted against the toroidal field energy, but splits into two branches when plotted against theRead More →

Machine learning methods for constructing probabilistic Fermi-LAT catalogs. (arXiv:2102.07642v2 [astro-ph.HE] UPDATED) <a href="http://arxiv.org/find/astro-ph/1/au:+Bhat_A/0/1/0/all/0/1">Aakash Bhat</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Malyshev_D/0/1/0/all/0/1">Dmitry Malyshev</a> Classification of sources is one of the most important tasks in astronomy. Sources detected in one wavelength band, for example using gamma rays, may have several possible associations in other wavebands or there may be no plausible association candidates. In this work, we aim to determine probabilistic classification of unassociated sources in the third and the fourth data release 2 Fermi Large Area Telescope (LAT) point source catalogs (3FGL and 4FGL-DR2) into two classes (pulsars and active galactic nuclei (AGNs)) or three classes (pulsars, AGNs, and other sources).Read More →

Black Hole and Galaxy Coevolution in Moderately Luminous Active Galactic Nuclei at z~1.4 in SXDF. (arXiv:2101.11273v2 [astro-ph.GA] UPDATED) <a href="http://arxiv.org/find/astro-ph/1/au:+Setoguchi_K/0/1/0/all/0/1">Kenta Setoguchi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ueda_Y/0/1/0/all/0/1">Yoshihiro Ueda</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Toba_Y/0/1/0/all/0/1">Yoshiki Toba</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Akiyama_M/0/1/0/all/0/1">Masayuki Akiyama</a> We investigate the relation of black hole mass versus host stellar mass and that of mass accretion rate versus star formation rate (SFR) in moderately luminous ($log L_{rm bol} sim 44.5-46.5 {rm erg s^{-1}}$), X-ray selected broad-line active galactic nuclei (AGNs) at $z=1.18-1.68$ in the Subaru/XMM-Newton Deep Field. The far-infrared to far-ultraviolet spectral energy distributions of 85 AGNs are reproduced with the latest version of Code Investigating GALaxy Emission ({tt CIGALE}), where the AGN clumpyRead More →

The z–DM distribution of fast radio bursts. (arXiv:2101.08005v2 [astro-ph.HE] UPDATED) <a href="http://arxiv.org/find/astro-ph/1/au:+James_C/0/1/0/all/0/1">C.W. James</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Prochaska_J/0/1/0/all/0/1">J.X. Prochaska</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Macquart_J/0/1/0/all/0/1">J.-P. Macquart</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+North_Hickey_F/0/1/0/all/0/1">F. North-Hickey</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bannister_K/0/1/0/all/0/1">K.W. Bannister</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dunning_A/0/1/0/all/0/1">A. Dunning</a> We develop a sophisticated model of FRB observations, accounting for the intrinsic cosmological gas distribution and host galaxy contributions, and give the most detailed account yet of observational biases due to burst width, dispersion measure, and the exact telescope beamshape. Our results offer a significant increase in both accuracy and precision beyond those previously obtained. Using results from ASKAP and Parkes, we present our best-fit FRB population parameters in a companion paper. Here, we consider in detailRead More →

SPHINCS_BSSN: A general relativistic Smooth Particle Hydrodynamics code for dynamical spacetimes. (arXiv:2012.13954v2 [gr-qc] UPDATED) <a href="http://arxiv.org/find/gr-qc/1/au:+Rosswog_S/0/1/0/all/0/1">S. Rosswog</a>, <a href="http://arxiv.org/find/gr-qc/1/au:+Diener_P/0/1/0/all/0/1">P. Diener</a> We present a new methodology for simulating self-gravitating general-relativistic fluids. In our approach the fluid is modelled by means of Lagrangian particles in the framework of a general-relativistic (GR) Smooth Particle Hydrodynamics (SPH) formulation, while the spacetime is evolved on a mesh according to the BSSN formulation that is also frequently used in Eulerian GR-hydrodynamics. To the best of our knowledge this is the first Lagrangian fully general relativistic hydrodynamics code (all previous SPH approaches used approximations to GR-gravity). A core ingredient of our particle-meshRead More →

Cosmology of the string derived flipped $SU(5)$. (arXiv:2011.09396v2 [hep-th] UPDATED) <a href="http://arxiv.org/find/hep-th/1/au:+Antoniadis_I/0/1/0/all/0/1">Ignatios Antoniadis</a>, <a href="http://arxiv.org/find/hep-th/1/au:+Nanopoulos_D/0/1/0/all/0/1">Dimitri V. Nanopoulos</a>, <a href="http://arxiv.org/find/hep-th/1/au:+Rizos_J/0/1/0/all/0/1">John Rizos</a> We study the cosmology of a string derived supersymmetric flipped $SU(5)$ model in the context of free-fermionic heterotic constructions that allow full calculability of the effective supergravity in perturbation theory around the fermionic vacuum where all string moduli have fixed values. The model has 3 generations of chiral families and a Higgs sector leading to particle phenomenology consistent with low energy data, that has been extensively studied in the past. Here, we show that it can also accommodate a novel successful cosmology, based on theRead More →

Resonant Shattering Flares as Multimessenger Probes of the Nuclear Symmetry Energy. (arXiv:2012.10322v2 [astro-ph.HE] UPDATED) <a href="http://arxiv.org/find/astro-ph/1/au:+Neill_D/0/1/0/all/0/1">Duncan Neill</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Newton_W/0/1/0/all/0/1">William G. Newton</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tsang_D/0/1/0/all/0/1">David Tsang</a> The behaviour of the nuclear symmetry energy near saturation density is important for our understanding of dense nuclear matter. This density dependence can be parameterised by the nuclear symmetry energy and its derivatives evaluated at nuclear saturation density. In this work we show that the core-crust interface mode of a neutron star is sensitive to these parameters, through the (density-weighted) shear-speed within the crust, which is in turn dependent on the symmetry energy profile of dense matter. We calculate the frequencyRead More →

Bounds on warm dark matter from Schwarzschild primordial black holes. (arXiv:2012.09867v2 [hep-ph] UPDATED) <a href="http://arxiv.org/find/hep-ph/1/au:+Auffinger_J/0/1/0/all/0/1">J&#xe9;r&#xe9;my Auffinger</a>, <a href="http://arxiv.org/find/hep-ph/1/au:+Masina_I/0/1/0/all/0/1">Isabella Masina</a>, <a href="http://arxiv.org/find/hep-ph/1/au:+Orlando_G/0/1/0/all/0/1">Giorgio Orlando</a> We consider light dark matter candidates originated from the evaporation of Schwarzschild primordial black holes, with masses in the range $10^{-5}-10^9$ g. These candidates are beyond Standard Model particles with negligible couplings to the other particles, so that they interact only gravitationally. Belonging to the category of warm dark matter, they nevertheless spoil structure formation, with a softer impact for increasing values of the candidate spin. Requiring such candidates to fully account for the observed dark matter, we find that the scenario ofRead More →

Fast neutrino flavor conversions in one-dimensional core-collapse supernova models with and without muon creation. (arXiv:2012.08525v2 [astro-ph.HE] UPDATED) <a href="http://arxiv.org/find/astro-ph/1/au:+Capozzi_F/0/1/0/all/0/1">Francesco Capozzi</a> (MPP Munich and Virginia Tech), <a href="http://arxiv.org/find/astro-ph/1/au:+Abbar_S/0/1/0/all/0/1">Sajad Abbar</a> (MPP Munich), <a href="http://arxiv.org/find/astro-ph/1/au:+Bollig_R/0/1/0/all/0/1">Robert Bollig</a> (MPA Garching), <a href="http://arxiv.org/find/astro-ph/1/au:+Janka_H/0/1/0/all/0/1">H.-Thomas Janka</a> (MPA Garching) In very dense environments, neutrinos can undergo fast flavor conversions on scales as short as a few centimeters provided that the angular distribution of the neutrino lepton number crosses zero. This work presents the first attempt to establish whether the non-negligible abundance of muons and their interactions with neutrinos in the core of supernovae can affect the occurrence of such crossings. For this purpose weRead More →

New Evidence for Extended HeII Reionization at z>3.5 from HeII Lyman Alpha and Beta Transmission Spikes. (arXiv:2012.07876v2 [astro-ph.CO] UPDATED) <a href="http://arxiv.org/find/astro-ph/1/au:+Makan_K/0/1/0/all/0/1">Kirill Makan</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Worseck_G/0/1/0/all/0/1">G&#xe1;bor Worseck</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Davies_F/0/1/0/all/0/1">Frederick B. Davies</a> (2), <a href="http://arxiv.org/find/astro-ph/1/au:+Hennawi_J/0/1/0/all/0/1">Joseph F. Hennawi</a> (3), <a href="http://arxiv.org/find/astro-ph/1/au:+Prochaska_J/0/1/0/all/0/1">J. Xavier Prochaska</a> (4), <a href="http://arxiv.org/find/astro-ph/1/au:+Richter_P/0/1/0/all/0/1">Philipp Richter</a> (1) ((1) Universit&#xe4;t Potsdam, (2) Max-Planck-Institut f&#xfc;r Astronomie, (3) University of California Santa Barbara, (4) University of California Santa Cruz) We present new high-resolution (R~14,000) spectra of the two brightest HeII-transparent quasars in the far-UV (FUV) at z>3.5, HE2QSJ2311-1417 (z=3.70) and HE2QSJ1630+0435 (z=3.81), obtained with the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST). In the predominantly saturatedRead More →

Effective N-body models of composite collisionless stellar systems. (arXiv:2012.06600v2 [astro-ph.GA] UPDATED) <a href="http://arxiv.org/find/astro-ph/1/au:+Nipoti_C/0/1/0/all/0/1">Carlo Nipoti</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cherchi_G/0/1/0/all/0/1">Giacomo Cherchi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Iorio_G/0/1/0/all/0/1">Giuliano Iorio</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Calura_F/0/1/0/all/0/1">Francesco Calura</a> Gas-poor galaxies can be modelled as composite collisionless stellar systems, with a dark matter halo and one or more stellar components, representing different stellar populations. The dynamical evolution of such composite systems is often studied with numerical N-body simulations, whose initial conditions typically require realizations with particles of stationary galaxy models. We present a novel method to conceive these N-body realizations, which allows one to exploit at best a collisionless N-body simulation that follows their evolution. The method is based on theRead More →

Wave optics of quantum gravity for light and particles. (arXiv:2012.02288v2 [gr-qc] UPDATED) <a href="http://arxiv.org/find/gr-qc/1/au:+Cherkas_S/0/1/0/all/0/1">S.L. Cherkas</a>, <a href="http://arxiv.org/find/gr-qc/1/au:+Kalashnikov_V/0/1/0/all/0/1">V.L. Kalashnikov</a> Effects of the quantum gravity under Minkowsky space-time background are considered. It is shown that despite the absence of the full theory of quantum gravity, very concrete and definite predictions could be made for the influence of the quantum gravitational fluctuations on the propagation of the particles and light. It is shown that the operator of the gravitational potential in a vacuum has the correlator $<0|hat Phi({bf r})hat Phi({bf r}^prime)|0>sim delta({bf r}-{bf r}^prime)/M_p^3$. As a result, nonrelativistic massive particle waves lose their coherence at a distance proportionalRead More →

Impact of Helical Electromagnetic Fields on the Axion Window. (arXiv:2012.00896v2 [astro-ph.CO] UPDATED) <a href="http://arxiv.org/find/astro-ph/1/au:+Kobayashi_T/0/1/0/all/0/1">Takeshi Kobayashi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Jain_R/0/1/0/all/0/1">Rajeev Kumar Jain</a> Primordial electromagnetic fields can strongly affect the cosmic evolution of axions, and vice versa. We show that if helical electromagnetic fields are coherently produced in the early universe, their remnants source a field velocity to the coupled axions and enhance the relic abundance of axion dark matter. We discuss the implications for the QCD axion and axion-like particles that are coupled to the SM or hidden gauge groups. For a QCD axion coupled to hidden photons, we find that the conventional window for the axion decayRead More →

Stochastic gravitational-wave background in quantum gravity. (arXiv:2012.00170v2 [gr-qc] UPDATED) <a href="http://arxiv.org/find/gr-qc/1/au:+Calcagni_G/0/1/0/all/0/1">Gianluca Calcagni</a>, <a href="http://arxiv.org/find/gr-qc/1/au:+Kuroyanagi_S/0/1/0/all/0/1">Sachiko Kuroyanagi</a> Among all cosmological quantum-gravity or quantum-gravity-inspired scenarios, only very few predict a blue-tilted primordial tensor spectrum. We explore five of them and check whether they can generate a stochastic gravitational-wave background detectable by present and future interferometers: non-local quantum gravity, string-gas cosmology, new ekpyrotic scenario, Brandenberger-Ho non-commutative inflation and multi-fractional spacetimes. We show that non-local quantum gravity is unobservable, while all the other models can reach the strain sensitivity of DECIGO but not that of LIGO-Virgo-KAGRA, LISA or Einstein Telescope. Other quantum-gravity models with red-tilted spectra (most loop quantum cosmologies)Read More →

Use of Excess Power Method and Convolutional Neural Network in All-Sky Search for Continuous Gravitational Waves. (arXiv:2011.12522v2 [gr-qc] UPDATED) <a href="http://arxiv.org/find/gr-qc/1/au:+Yamamoto_T/0/1/0/all/0/1">Takahiro S. Yamamoto</a>, <a href="http://arxiv.org/find/gr-qc/1/au:+Tanaka_T/0/1/0/all/0/1">Takahiro Tanaka</a> The signal of continuous gravitational waves has a longer duration than the observation period. Even if the waveform in the source frame is monochromatic, we will observe the waveform with modulated frequencies due to the motion of the detector. If the source location is unknown, a lot of templates having different sky positions are required to demodulate the frequency, and the required huge computational cost restricts the applicable parameter region of coherent search. In this work, we propose andRead More →

Revisiting the structure function of PSR B0950+08 scintillations. (arXiv:2103.06811v1 [astro-ph.GA]) <a href="http://arxiv.org/find/astro-ph/1/au:+Goldman_I/0/1/0/all/0/1">Itzhak Goldman</a> The observational structure function of the scintillations of the radio pulsar PSR B0950+08, was fitted, a decade ago, with a power law with index $1 pm 0.01$. This was interpreted as an {em appreciable deviation} from the, commonly observed index of $5/3$, expected for Kolmogorov turbulence. In this paper it is suggested that the observations are consistent with a Kolmogorov turbulence and that the {em apparent} deviation is due to a turbulent region with an effective depth which is {em comparable} to the observed lateral scales on the plane of the sky,Read More →

Novel null tests for the spatial curvature and homogeneity of the Universe and their machine learning reconstructions. (arXiv:2103.06789v1 [astro-ph.CO]) <a href="http://arxiv.org/find/astro-ph/1/au:+Arjona_R/0/1/0/all/0/1">Rub&#xe9;n Arjona</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Nesseris_S/0/1/0/all/0/1">Savvas Nesseris</a> A plethora of observational data obtained over the last couple of decades has allowed cosmology to enter into a precision era and has led to the foundation of the standard cosmological constant and cold dark matter paradigm, known as the $Lambda$CDM model. Given the many possible extensions of this concordance model, we present here several novel consistency tests which could be used to probe for deviations from $Lambda$CDM. First, we derive a joint consistency test for the spatial curvature $Omega_{k,0}$Read More →

No Black Holes in NGC 6397. (arXiv:2103.06273v1 [astro-ph.GA]) <a href="http://arxiv.org/find/astro-ph/1/au:+Rui_N/0/1/0/all/0/1">Nicholas Z. Rui</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Weatherford_N/0/1/0/all/0/1">Newlin Weatherford</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kremer_K/0/1/0/all/0/1">Kyle Kremer</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chatterjee_S/0/1/0/all/0/1">Sourav Chatterjee</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fragione_G/0/1/0/all/0/1">Giacomo Fragione</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Rasio_F/0/1/0/all/0/1">Frederic A. Rasio</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Rodriguez_C/0/1/0/all/0/1">Carl L. Rodriguez</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ye_C/0/1/0/all/0/1">Claire S. Ye</a> Recently, citet{vitral2021does} detected a central concentration of dark objects in the core-collapsed globular cluster NGC 6397, which could be interpreted as a subcluster of stellar-mass black holes. However, it is well established theoretically that any significant number of black holes in the cluster would provide strong dynamical heating and is fundamentally inconsistent with this cluster’s core-collapsed profile. Claims of intermediate-mass black holes in core-collapsed clusters should similarly be treatedRead More →

Radio Observations of an Ordinary Outflow from the Tidal Disruption Event AT2019dsg. (arXiv:2103.06299v1 [astro-ph.HE]) <a href="http://arxiv.org/find/astro-ph/1/au:+Cendes_Y/0/1/0/all/0/1">Y. Cendes</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Alexander_K/0/1/0/all/0/1">K. D. Alexander</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Berger_E/0/1/0/all/0/1">E. Berger</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Eftekhari_T/0/1/0/all/0/1">T. Eftekhari</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Williams_P/0/1/0/all/0/1">P. K. G. Williams</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chornock_R/0/1/0/all/0/1">R. Chornock</a> We present detailed radio observations of the tidal disruption event (TDE) AT2019dsg, obtained with the Very Large Array (VLA) and the Atacama Large Millimeter/submillimeter Array (ALMA), and spanning $55-560$ days post-disruption. We find that the peak brightness of the radio emission increases until ~200 days and subsequently begins to decrease steadily. Using the standard equipartition analysis, including the effects of synchrotron cooling as determined by the joint VLA-ALMA spectral energyRead More →