Papers for Friday, Dec 29 2023

We present results from the search for astrometric accelerations of stars in $\omega$ Centauri using 13 years of regularly-scheduled {\it Hubble Space Telescope} WFC3/UVIS calibration observations in the cluster core. The high-precision astrometry of $\sim$160\,000 sources was searched for significant deviations from linear proper motion. This led to the discovery of four cluster members and one foreground field star with compelling acceleration patterns. We interpret them as the result of the gravitational pull by an invisible companion and determined preliminary Keplerian orbit parameters, including the companion's mass. {For the cluster members} our analysis suggests periods ranging from 8.8 to 19+ years and dark companions in the mass range of $\sim$0.7 to $\sim$1.4$M_\mathrm{sun}$. At least one companion could exceed the upper mass-boundary of white dwarfs and can be classified as a neutron-star candidate.

Context: Episodic accretion plays an important role during the early phases of star-formation. The main processes responsible for the episodic accretion events remain, however, unclear. Aims: Our main objective is to investigate the properties of FUors and EXors by analysing observational data, along with numerical hydrodynamics simulations of protostellar disks, stellar evolution models of outbursting stars and thermo-chemical models of star-disk systems in the outburst state. Our goal is to get a better understanding of the outburst processes and their respective origin. Methods: We used the radiation thermo-chemical code ProDiMo (PROtoplanetary DIsk MOdel) to match the dust emission and gas emission lines originating from the environment surrounding the FUor star Re 50 N IRS 1. Our model focusses on the observational data obtained by Herschel and Spitzer while we use archival photometry to complete the spectral energy distribution. Results: The modelling shows that the object is composed of a complex combination of several heating sources with different spatial distribution. Our model uses a massive envelope with an mass infall rate of 1.35 $\times 10^{-5}$ M$_{sun}$ yr$^{-1}$ to explain the continuum emission in the (sub-)mm regime. At the same time we fit the CO and $^{13}$CO ladders from 60 \textmu m to 650 \textmu m along with the two [\ion{O}{i}] lines centered at 63.18 and 145.53 \textmu m. To explain the strong CO emission at shorter wavelengths and the oxygen lines, we require a very warm disk due to a high disk accretion rate reaching 6 $\times 10^{-4}$ M$_{sun}$ yr$^{-1}$ and an additional UV field of 3\% of the overall emission to heat the disk.

We present microscopic Molecular Dynamics simulations including the efficient Ewald sum procedure to study warm and dense stellar plasmas consisting of finite-size ion charges immerse in a relativistic neutralizing electron gas. For densities typical of Supernova matter and crust in a proto-neutron star, we select a representative single ion composition and obtain the virialized equation of state (vEoS). We scrutinize the finite-size and screening corrections to the Coulomb potential appearing in the virial coefficients $B_2, B_3$ and $B_4$ as a function of temperature. In addition, we study the thermal heat capacity at constant volume, $C_V$, and the generalized Mayer's relation i.e. the difference $C_P-C_V$ with $C_P$ being the heat capacity at constant pressure, obtaining clear features signaling the onset of the liquid-gas phase transition. Our findings show that microscopic simulations reproduce the discontinuity in $C_V$, whose value lies between that of idealized gas and crystallized configurations. We study the pressure isotherms marking the boundary of the metastable region before the gaseous transition takes place. The resulting vEoS displays a behaviour where effective virial coefficients include extra density dependence showing a generalized density-temperature form. As an application we parametrize pressure as a function of density and temperature under the form of an artificial neural network showing the potential of machine learning for future regression analysis in more refined multicomponent approaches. This is of interest to size the importance of these corrections in the liquid-gas phase transition in warm and dense plasma phases contributing to the cooling behaviour of early Supernova phases and proto-neutron stars.

Gamma-ray bursts (GRBs) are fascinating sources studied in modern astronomy. They are extremely luminous electromagnetic explosions in the Universe observed from cosmological distances. These unique characteristics provide a marvellous chance to study the evolution of massive stars and probe the rarely explored early Universe. In addition, the central source's compactness and the high bulk Lorentz factor in GRB's ultra-relativistic jets make them efficient laboratories for studying high-energy astrophysics. GRBs are the only astrophysical sources observed in two distinct signals: gravitational and electromagnetic waves. GRBs are believed to be produced from a "fireball" moving at a relativistic speed, launched by a fast-rotating black hole or magnetar. GRBs emit radiation in two phases: the initial gamma/hard X-rays prompt emission, the duration of which ranges from a few seconds to hours, followed by the multi-wavelength and long-lived afterglow phase. Based on the observed time frame of GRB prompt emission, astronomers have generally categorized GRBs into two groups: long (> 2 s) and short (< 2 s) bursts. Despite the discovery of GRBs in the late 1960s, their origin is still a great mystery. There are several open questions related to GRBs, such as: What powers the GRBs jets/central engine? What are the possible progenitors? What is the jet composition? What is the underlying emission process that gives rise to observed radiation? Where and how does the energy dissipation occur in the outflow? How to solve the radiative efficiency problem? What are the possible causes of Dark GRBs and orphan afterglows? How to investigate the local environment of GRBs? etc. In this thesis, we explored some of these open enigmas (progenitor, emission mechanisms, jet composition and environment) using multi-wavelength observations obtained using space and ground-based facilities.

Core-collapse supernovae (CCSNe) are catastrophic astrophysical phenomena that occur during the last evolutionary stages of massive stars having initial masses of around 8 M$_{\odot}$ or more. These calamitous events play a pivotal role in enriching our Universe with heavy elements and are also responsible for the birth of Neutron stars and stellar mass Black holes. Knowledge of the possible progenitors of CCSNe is fundamental to understanding these transient events. Additionally, the underlying circumstellar environment around possible progenitors and the physical mechanism powering the light curves of these catastrophic CCSN events also require careful investigations to unveil their nature. The research work within the context of the present thesis is an attempt to investigate the possible progenitors, ambient media around the progenitors, and powering mechanisms behind the light curve of CCSNe.

We present a new subgrid model for neutrino quantum kinetics, which is primarily designed to incorporate effects of collective neutrino oscillations into neutrino-radiation-hydrodynamic simulations for core-collapse supernovae and mergers of compact objects. We approximate the neutrino oscillation term in quantum kinetic equation by Bhatnagar-Gross-Krook (BGK) relaxation-time prescription, and the transport equation is directly applicable for classical neutrino transport schemes. The BGK model is motivated by recent theoretical indications that non-linear phases of collective neutrino oscillations settle into quasi-steady structures. We explicitly provide basic equations of the BGK subgrid model for both multi-angle and moment-based neutrino transport to facilitate the implementation of the subgrid model in the existing neutrino transport schemes. We also show the capability of our BGK subgrid model by comparing to fully quantum kinetic simulations for fast neutrino-flavor conversion. We find that the overall properties can be well reproduced in the subgrid model; the error of angular-averaged survival probability of neutrinos is within $\sim 20 \%$. By identifying the source of error, we also discuss perspectives to improve the accuracy of the subgrid model.

Spatial variations in survey properties due to selection effects generate substantial systematic errors in large-scale structure measurements in optical galaxy surveys on very large scales. On such scales, the statistical sensitivity of optical surveys is also limited by their finite sky coverage. By contrast, gravitational wave (GW) sources appear to be relatively free of these issues, provided the angular sensitivity of GW experiments can be accurately characterized. We quantify the expected cosmological information gain from combining the forecast LSST 3$\times$2pt analysis (combination of three 2-point correlations of galaxy density and weak lensing shear fields) with the large-scale auto-correlation of GW sources from proposed next-generation GW experiments. We find that in $\Lambda$CDM and $w$CDM models, there is no significant improvement in cosmological constraints from combining GW with LSST 3$\times$2pt over LSST alone, due to the large shot noise for the former; however, this combination does enable a $\sim6\%$ constraint on the linear galaxy bias of GW sources. More interestingly, the optical-GW data combination provides tight constraints on models with primordial non-Gaussianity (PNG), due to the predicted scale-dependent bias in PNG models on large scales. Assuming that the largest angular scales that LSST will probe are comparable to those in Stage III surveys ($\ell_{\rm min}\sim50$), the inclusion of next-generation GW measurements could improve constraints on the PNG parameter $f_{\rm NL}$ by up to a factor of $\simeq6.6$ compared to LSST alone, yielding $\sigma(f_{\rm NL})=8.5$. These results assume the expected capability of a network of Einstein Telescope-like GW observatories, with a detection rate of $10^6$ events/year. We investigate the sensitivity of our results to different assumptions about future GW detectors as well as different LSST analysis choices.

Gravitational waves (GWs) provide a new avenue to test Einstein's General Relativity (GR) using the ongoing and upcoming GW detectors by measuring the redshift evolution of the effective Planck mass proposed by several modified theories of gravity. We propose a model-independent, data-driven approach to measure any deviation from GR in the GW propagation effect by combining multi-messenger observations of GW sources accompanied by EM counterparts, commonly known as bright sirens (Binary Neutron Star(BNS) and Neutron Star Black Hole systems(NSBH)). We show that by combining the GW luminosity distance measurements from bright sirens with the Baryon Acoustic Oscillation (BAO) measurements derived from galaxy clustering, and the sound horizon measurements from the Cosmic Microwave Background (CMB), we can make a data-driven reconstruction of deviation of the variation of the effective Planck mass (jointly with the Hubble constant) as a function of cosmic redshift. Using this technique, we achieve a precise measurement of GR with redshift (z) with a precision of approximately $7.9\%$ for BNSs at redshift $z=0.075$ and $10\%$ for NSBHs at redshift $z=0.225$ with 5 years of observation from LVK network of detectors. Employing $CE\&ET$ for just 1 year yields the best precision of about $1.62\%$ for BNSs and $2\%$ for NSBHs at redshift $z=0.5$ on the evolution of the frictional term, and a similar precision up to $z=1$. This measurement can discover potential deviation from any kind of model that impacts GW propagation with ongoing and upcoming observations.

Gravitational waves (GW) from the inspiral of binary compact objects offers a one-step measurement of the luminosity distance to the event, which is essential for the measurement of the Hubble constant, $H_0$, that characterizes the expansion rate of the Universe. However, unlike binary neutron stars, the inspiral of binary black holes is not expected to be accompanied by electromagnetic radiation and a subsequent determination of its redshift. Consequently, independent redshift measurements of such GW events are necessary to measure $H_0$. In this study, we present a novel Bayesian approach to infer $H_0$ from the cross-correlation between galaxies with known redshifts and individual binary black hole merger events. We demonstrate the efficacy of our method with $250$ simulated GW events distributed within $1$ Gpc in colored Gaussian noise of Advanced LIGO and Advanced Virgo detectors operating at O4 sensitivity. We show that such measurements can constrain the Hubble constant with a precision of $\lesssim 15 \%$ ($90\%$ highest density interval). We highlight the potential improvements that need to be accounted for in further studies before the method can be applied to real data.

Primordial magnetic fields (PMFs) are one of the plausible candidates for the origin of the observed large-scale magnetic fields. While many proposals have been made for the generation mechanism of PMFs by earlier studies, it remains a subject of debate. In this paper, to obtain new insights into PMFs, we focus on the intrinsic alignments (IAs) of galaxies induced by the vector and tensor modes of the anisotropic stress of PMFs. The long-wavelength vector and tensor modes locally induce the tidal gravitational fields, leading to the characteristic distortions of the intrinsic ellipticity of galaxies. We investigate the shear E- and B-mode power spectra induced by the magnetic vector and tensor modes in the three-dimensional space, assuming the combination of galaxy imaging and galaxy redshift surveys. We find that the magnetic tensor mode dominates both the E- and B-mode spectra. In particular, the B-mode spectrum induced by the magnetic tensor mode plays a crucial role in constraining the amplitude of PMFs, even in the presence of the non-magnetic scalar contribution to the B-mode spectrum arising from the one-loop effect. In future galaxy redshift surveys, such as Euclid and Square Kilometre Array, the minimum detectable value reaches $\sim 30 \, \rm nG$, which can potentially get even smaller in proportion to the number of observed galaxies and reach $\sim \mathcal{O}(1 \, {\rm nG})$. Measuring the IAs of galaxies would be a potential probe for PMFs in future galaxy surveys.

Currently, 6 out of 30 known magnetars had pulsed radio emission detected. In this work, we evaluated the possibility of detecting radio transient events from magnetars with the telescopes of the Instituto Argentino de Radioastronom\'ia (IAR). To this aim, we made daily observations of the magnetar XTE~J1810$-$197 from 02-Sep-22 to 30-Nov-22. We analysed the observations by applying ephemeris folding and single pulse searches. We fitted a timing model to our observations and were able to detect the magnetar on 6 of the 36 observing sessions with signal-to-noise ratios at the limit of detectability, $3.3\leq \mathrm{S/N} \leq4.1$. We searched for individual pulses in one of these 6 days and found 7 individual pulses with $8.5\leq \mathrm{S/N} \leq18.8$. The dispersion measure changed slightly between pulses within a range of $178 \leq \textrm{DM} \,[\mathrm{pc\, cm^{-3}}] \leq 182$. The pulse with $\mathrm{S/N}=18.8$ has an associated $\textrm{DM}$ of $180\,\mathrm{pc\, cm^{-3}}$. We confirmed that we can detect pulsed radio emission in the band of $1400-1456\, \mathrm{MHz}$ from magnetars with a time resolution of $146\,\mu s$, being able to detect both integrated pulse profiles and individual pulses.

Iron K$\alpha$ (Fe K$\alpha$) emission is observed ubiquitously in AGN, and it is a powerful probe of their circumnuclear environment. Examinations of the emission line play a pivotal role in understanding the disk geometry surrounding the black hole. It has been suggested that the torus and the broad line region (BLR) are the origins of emission. However, there is no universal location for the emitting region relative to the BLR. Here, we present an analysis of the narrow component of the Fe K$\alpha$ line in the Seyfert AGN MCG-5-23-16, one of the brightest AGN in X-rays and in Fe K$\alpha$ emission, to localize the emitting region. Spectra derived from Chandra/HETGS observations show asymmetry in the narrow Fe K$\alpha$ line, which has only been confirmed before in the AGN NGC 4151. Models including relativistic Doppler broadening and gravitational redshifts are preferred over simple Gaussians and measure radii consistent with $R \simeq$ 200-650 r$_g$. These results are consistent with those of NGC 4151 and indicate that the narrow Fe K$\alpha$ line in MCG-5-23-16 is primarily excited in the innermost part of the optical broad line region (BLR), or X-ray BLR. Characterizing the properties of the narrow Fe K$\alpha$ line is essential for studying the disk geometries of the AGN population and mapping their innermost regions.

Pulsar detection has become an active research topic in radio astronomy recently. One of the essential procedures for pulsar detection is pulsar candidate sifting (PCS), a procedure of finding out the potential pulsar signals in a survey. However, pulsar candidates are always class-imbalanced, as most candidates are non-pulsars such as RFI and only a tiny part of them are from real pulsars. Class imbalance has greatly damaged the performance of machine learning (ML) models, resulting in a heavy cost as some real pulsars are misjudged. To deal with the problem, techniques of choosing relevant features to discriminate pulsars from non-pulsars are focused on, which is known as {\itshape feature selection}. Feature selection is a process of selecting a subset of the most relevant features from a feature pool. The distinguishing features between pulsars and non-pulsars can significantly improve the performance of the classifier even if the data are highly imbalanced.In this work, an algorithm of feature selection called {\itshape K-fold Relief-Greedy} algorithm (KFRG) is designed. KFRG is a two-stage algorithm. In the first stage, it filters out some irrelevant features according to their K-fold Relief scores, while in the second stage, it removes the redundant features and selects the most relevant features by a forward greedy search strategy. Experiments on the dataset of the High Time Resolution Universe survey verified that ML models based on KFRG are capable for PCS, correctly separating pulsars from non-pulsars even if the candidates are highly class-imbalanced.

A previously unremarkable star near the Canis Major OB1/R1 association underwent an episode of multiple deep brightness minima. Light curves based on archival Gaia, ZTF, NEOWISE data and additional observations from LCO and UKIRT show that the star was not variable prior to 2019 Aug 18 (MJD 58700), and on that date started showing brightness dips of up to 3 magnitudes in the Gaia G and ZTF r bandpasses. After MJD 59500, ~800 days after the onset of these dipping events, the star returned to its previous brightness, and no significant dipping events have been recorded since. Compared to the stable phase, NEOWISE infrared photometry in the W1 and W2 bands indicates a generally redder color, and both decreases and increases in brightness at different times during the dipping episode. The spectrum of Gaia21bcv taken after the end of the dipping episode shows several neutral and ionized metal absorption lines, including Li, indicating a spectral type of ~ K5. Variable emission from [OI] was observed. The H alpha absorption in Gaia21bcv is too faint and irregular for this spectral type, indicating that the line is partly filled in by variable emission, a signature of weak episodic accretion. Gaia21bcv lies above the zero-age main sequence, but is much fainter than typical R CrB stars. We interpret the light curve of Gaia21bcv as being similar to the occultation events in Epsilon Aurigae, i.e., occultation by a disk around a companion object orbiting the primary star.

High precision mapping of H2O megamaser emissions from active galaxies have revealed more than a dozen of Keplerian H2O aser disks that enable a ~4% Hubble constant measurement and provide accurate black hole masses. The maser disks that allow for these important astrophysical applications usually display clear inner and outer edges at sub-parsec scales. It is still unclear what causes these boundaries and how their radii are determined. To understand whether the physical conditions favorable for population inversion of H2O molecules can determine the inner and outer radii of a maser disk, we examine the distributions of gas density and X-ray heating rate in a warped molecular disk described by power-law surface density profile. With a suitable choice of the disk mass, we find that the outer radius R_out of the maser disk predicted from our model can match the observed value, with R_out mainly determined by the maximum heating rate or the minimum density for efficient maser action, depending on the combination of the Eddington ratio, black hole mass and disk mass. Our analysis also suggests that the inner edge of a maser disk often lie close to the dust sublimation radius, suggesting that the physical conditions of the dusts may play a role in defining inner boundary of the disk. Finally, our model predicts that H2O "gigamaser" disks could possibly exist at the center of high-z quasars, with disk size of >~10-30 pc.

System parameters are re-determined: $M_1=0.86\pm0.18M\odot$, $M_2=0.103\pm0.022M\odot$, $A=1.508\pm 0.100\times 10^{10}$cm, and $i=69\pm3^{\circ}$. The secondary component is a semi-degenerate helium star loosing mass at a rate $\dot M=4.93\pm 1.65\times10^{-9}M\odot/yr$. The accretion disk is sufficiently hot to avoid thermal instability. The orbital light curve recovered from observations made in 1962 shows minimum shifted to phase $\phi=0.50$, corresponding to $O-C=0.0060$d. Together with mimima observed in 1992-99 this implies that the orbital period is increasing at a rate $dP/dt\approx 8.5 \times 10^{-13}$ consistent with predictions involving the emission of gravitational waves.

We investigate the relation between turbulence and magnetic field switchbacks in the inner heliosphere below 0.5 AU in a distance and scale dependent manner. The analysis is performed by studying the evolution of the magnetic field vector increments and the corresponding rotation distributions, which contain the switchbacks. We find that the rotation distributions evolve in a scale dependent fashion, having the same shape at small scales independent of the radial distance, contrary to at larger scales where the shape evolves with distance. The increments are shown to evolve towards a log-normal shape with increasing radial distance, even though the log-normal fit works quite well at all distances especially at small scales. The rotation distributions are shown to evolve towards the Zhdankin et al. (2012) rotation model moving away from the Sun. The magnetic switchbacks do not appear at any distance as a clear separate population. Our results suggest a scenario in which the evolution of the rotation distributions, including switchbacks, is primarily the result of the expansion driven growth of the fluctuations, which are reshaped into a log-normal distribution by the solar wind turbulence.

The correlation between the X-ray and UV luminosities observed in quasars, spanning a wide redshift range and holding true for several decades in both spectral bands, suggests the presence of a universal mechanism governing the transfer of energy from the accretion disc to the hot corona. In this study, we leverage X-ray spectroscopic data extracted from the Chandra Source Catalog 2.0 for a sample of over $2000$ quasars from the Sloan Digital Sky Survey Data Release 14 (SDSS DR14). Our analysis reveals a reduced intrinsic dispersion in the $L_{\rm{X}}-L_{\rm{UV}}$ relation at higher redshifts ($\delta < 0.2$ dex) compared to previous studies relying on photometric data from catalogs. Additionally, our findings confirm the stability of this relation up to redshifts of approximately $4.5$. The $L_{\rm{X}}-L_{\rm{UV}}$ relation can also serve as a tool to investigate the physics of accretion by identifying outliers - sources that exhibit a different state of the accretion disc-hot corona system compared to the average population. For instance, X-ray-weak quasars are sources with reduced X-ray emissions due to a radiatively inefficient state of the corona, and their optical properties suggest the presence of a powerful accretion disc wind. The wealth of spectroscopic data available in the CSC 2.0-SDSS catalogs opens up the opportunity for a more comprehensive exploration of the central engine in AGN.

We investigate the relationship between the baryonic angular momentum and mass for a sample of 36 isolated disc galaxies with resolved HI kinematics and infrared WISE photometry drawn from -- and representative in terms of morphologies, stellar masses and HI-to-star fraction of -- the carefully-constructed AMIGA sample of isolated galaxies. Similarly to previous studies performed on non-isolated galaxies, we find that the relation is well described by a power law $j_{bar} \propto M_{bar}^\alpha$. We also find a slope of $\alpha = 0.54 \pm 0.08$ for the AMIGA galaxies, in line with previous studies in the literature; however, we find that the specific angular momenta of the AMIGA galaxies are on average higher than those of non-isolated galaxies in the literature. This is consistent with theories stipulating that environmental processes involving galaxy-galaxy interaction are able to impact the angular momentum content of galaxies. However, no correlation was found between the angular momentum and the degree of isolation, suggesting that there may exist a threshold local number density beyond which the effects of the environment on the angular momentum become important.

Radiation flow through an inhomogeneous medium is critical in a wide range of physics and astronomy applications from transport across cloud layers on the earth to the propagation of supernova blast-waves producing UV and X-ray emission in supernovae. This paper reviews the current state of the art in the modeling of inhomogeneous radiation transport, subgrid models developed to capture this often-unresolved physics, and the experiments designed to improve our understanding of these models. We present a series of detailed simulations (both single-clump and multi-clump conditions) probing the dependence on the physical properties of the radiation front (e.g. radiation energy) and material characteristics (specific heat, opacity, clump densities). Unless the radiation pressure is high, the clumps will heat and then expand, effectively cutting off the radiation flow. The expanding winds can also produce shocks that generates high energy emission. We compare our detailed simulations with some of the current subgrid prescriptions, identifying some of the limitations of these current models.

The Far Ultraviolet (FUV: hereafter 900-1150 A) is a spectral range which contains many of the ground state transitions of common elements but has had limited observational capabilities due to the unique technological requirements to operate in this waveband. Conceptual designs are presented, for high resolution (R > 50,000) echelle spectrographs for CubeSat, SMEX and MIDEX missions, along with comparisons of their performance to past instruments.

The Vera C. Rubin Observatory is slated to observe nearly 20 billion galaxies during its decade-long Legacy Survey of Space and Time. The rich imaging data it collects will be an invaluable resource for probing galaxy evolution across cosmic time, characterizing the host galaxies of transient phenomena, and identifying novel populations of anomalous systems. To facilitate these studies, we introduce a convolutional variational autoencoder trained to estimate the redshift, stellar mass, and star-formation rates of galaxies from multi-band imaging data. We train and test our physics-informed CVAE on a spectroscopic sample of $\sim$26,000 galaxies within $z<1$ imaged through the Dark Energy Camera Legacy Survey. We show that our model can infer redshift and stellar mass more accurately than the latest image-based self-supervised learning approaches, and is >100x faster than more computationally-intensive SED-fitting techniques. Using a small sample of Green Pea and Red Spiral galaxies reported in the literature, we further demonstrate how this CVAE can be used to rapidly identify rare galaxy populations and interpret what makes them unique.

Recent JWST surveys reveal a striking abundance of massive galaxies at cosmic dawn, earlier than predicted by $\Lambda$CDM. The implied speed-up in galaxy formation by gravitational collapse is reminiscent of short-period galaxy dynamics described by the baryonic Tully-Fisher relation. This may originate in weak gravitation tracking the de Sitter scale of acceleration $a_{dS}=cH$, where $c$ is the velocity of light and $H(z)\propto \left(1+z\right)^{3/2}$ is the Hubble parameter with redshift $z$. With no free parameters, this produces a speed-up in early galaxy formation by an order of magnitude with essentially no change in initial galaxy mass function. It predicts a deceleration parameter $q_0=1-\left( 2\pi/GAa_{dS}\right)^2 = -0.98\pm 0.5$, where $G$ is Newton's constant and $A=(47\pm6)M_\odot$\,(km/s)$^{-4}$ is the baryonic Tully-Fisher coefficient (McGaugh 2012). At $3\sigma$ significance, it identifies dynamical dark energy alleviating $H_0$-tension when combined with independent $q_0$ estimates in the Local Distance Ladder. Conclusive determination of $q_0=d\log(\theta(z)H(z))/dz\left|_{z=0}\right.$ is expected from BAO angle $\theta(z)$ observations by the recently launched {\em Euclid} mission.

Star-forming galaxies (SFGs) adhere to a surprisingly tight scaling relation of dust attenuation parameterized by the infrared excess (IRX=$L_{\rm IR}/L_{\rm UV}$), being jointly determined by the star formation rate (SFR), galaxy size ($R_{\rm e}$), metallicity ($Z$/Z$_\odot$) and axial ratio ($b/a$). We examine how these galaxy parameters determine the effective dust attenuation and give rise to the universal IRX relation, utilizing a simple two-component star-dust geometry model in which dust in the dense and diffuse interstellar medium (ISM) follows exponential mass density profiles, connected with but not necessarily identical to the stellar mass profiles. Meanwhile, empirical relations are adopted to link galaxy properties, including the gas--star formation relation, the dust-to-stellar size relation, as well as the dust-to-gas ratio versus metallicity relation. By fitting a large sample of local SFGs with the model, we obtain the best-fitting model parameters as a function of metallicity, showing that the two-component geometry model is able to successfully reproduce the dependence of IRX on SFR, $R_{\rm e}$, $b/a$ at given $Z$/Z$_\odot$, as well as the dependence of power-law indices on metallicity. Moreover, we also retrieve constraints on the model geometry parameters, including the optical depth of birth clouds (BCs), BC-to-total dust mass fraction, BC covering factor of UV-emitting stars, and star-to-total dust disc radius ratio, which all evolve with galaxy metallicity. Finally, a consistent picture of how the star-dust geometry in SFGs evolves with galaxy metallicity is discussed.

The discovery in 2014 of the pulsation from the ultra-luminous X-ray source (ULX) M82 X-2 in 2014 has changed our view of ULXs. Because of the relatively short baseline over which pulsations have been detected so far, M82 X-2's spin state had been assumed to be in an equilibrium state. Using \cha and \xmm archive data, we are able to investigate the pulsation of M82 X-2 back to 2005 and 2001. The newly determined spin frequencies clearly show a long-term spin-down trend. If this trend is caused by magnetic threading, we infer a dipolar magnetic field of $\sim1.2\times10^{13}$ G and that a mild beaming factor ($\sim4$) is needed to match the braking torque with the mass accretion torque. On the other hand, there are \nus observations showing instantaneous spin-down behaviours, which might favour a variable prograde/retrograde flow scenario for M82 X-2.

Since the commencement of the first SETI observation in 2019, China's Search for Extraterrestrial Intelligence program has garnered momentum through domestic support and international collaborations. Several observations targeting exoplanets and nearby stars have been conducted with the FAST. In 2023, the introduction of the Far Neighbour Project(FNP) marks a substantial leap forward, driven by the remarkable sensitivity of the FAST telescope and some of the novel observational techniques. The FNP seeks to methodically detect technosignatures from celestial bodies, including nearby stars, exoplanetary systems, Milky Way globular clusters, and more. This paper provides an overview of the progress achieved by SETI in China and offers insights into the distinct phases comprising the FNP. Additionally, it underscores the significance of this project's advancement and its potential contributions to the field.

We present the structure of a low angular momentum accretion flows around rotating compact objects incorporating relativistic corrections up to the leading post-Newtonian order. To begin with, we formulate the governing post-Newtonian hydrodynamic equations for the mass and energy-momentum flux without imposing any symmetries. However, for the sake of simplicity, we consider the flow to be stationary, axisymmetric, and inviscid. Toward this, we adapt the polytropic equation of state (EoS) and analyze the geometrically thin accretion flow confined to the equatorial plane. The spin-orbit effects manifest themselves in the disk structure. This is a relativistic interaction between the body's spin and the motion of fluid elements inside the gravitational potential of the body. In the present analysis, we focus on global transonic accretion solutions, where a subsonic flow enters far away from the compact object and gradually gains radial velocity as it moves inwards. Thus, the flow becomes supersonic after reaching a certain radius, known as the critical point. For a better understanding of the transonic solutions, we classify the post-Newtonian equations into semi-relativistic (SR), semi-Newtonian (SN), and non-relativistic (NR) limits and compare the accretion solutions and their corresponding flow variables. With these, we find that SR and SN flow are in good agreement all throughout, although they deviate largely from the NR ones. Interestingly, the density profile seems to follow the profile $\rho \propto r^{-3/2}$ in the post-Newtonian regime. The present study has the potential to connect Newtonian and GR descriptions of accretion disks.

We present three-dimensional (3D) maps of Jupiter's atmospheric circulation at cloud-top level from Doppler-imaging data obtained in the visible domain with JIVE, the second node of the JOVIAL network, which is mounted on the Dunn Solar Telescope at Sunspot, New Mexico. We report on 12 nights of observations between May 4 and May 30, 2018, representing a total of about 80 hours. Firstly, the average zonal wind profile derived from our data is compatible with that derived from cloud-tracking measurements performed on Hubble Space Telescope images obtained in April 2018 from the Outer Planet Atmospheres Legacy (OPAL) program. Secondly, we present the first ever two-dimensional maps of Jupiter's atmospheric circulation from Doppler measurements. The zonal velocity map highlights well-known atmospheric features, such as the equatorial hot spots and the Great Red Spot (GRS). In addition to zonal winds, we derive meridional and vertical velocity fields from the Doppler data. The motions attributed to vertical flows are mainly located at the boundary between the equatorial belts and tropical zones, which could indicate active motion in theses regions. Qualitatively, these results compare well to recent Juno data that have unveiled the three-dimensional structure of Jupiter's wind field. To the contrary, the motions attributed to meridional circulation are very different from what is obtained by cloud tracking, except at the GRS. Because of limitations with data resolution and processing techniques, we acknowledge that our measurement of vertical or meridional flows of Jupiter are still to be confirmed.

Novae, explosive events in binary star systems involving a white dwarf and a companion star, offer profound insights into extreme astrophysical conditions. During the eruption of a nova, material accreted onto the white dwarf's surface undergoes a thermonuclear runaway reaction resulting in the ejection of matter into space and the formation of a luminous shell. The classical V5668 Sgr (Nova Sagittarii) was the second and brighter of the two novae in the southern constellation of Sagittarius. It was discovered by John Seach of Chatsworth Island, Australia, on March 15, 2015. In this paper, drawing on data from Karl G. Jansky Very Large Array, the US-based radio astronomy observatory, on V5668 Sgr as well as from research that aggregates data from a range of sources including telescope archives, this study used the Uniform Slab Model and statistical techniques to plot the nova's light and frequency curves and estimate its ejected shell mass and the brightness temperature. These characteristics help us better understand the nova's formation and eruption. The paper presents the light curves in a machine-readable format and provides insight into the behaviour of ionised gas clouds.

The angular momentum of molecular cloud cores plays a key role in the star formation process. However, the evolution of the angular momentum of molecular cloud cores formed in magnetized molecular filaments is still unclear. In this paper, we perform three-dimensional magnetohydrodynamics simulations to reveal the effect of the magnetic field on the evolution of the angular momentum of molecular cloud cores formed through filament fragmentation. As a result, we find that the angular momentum decreases by 30% and 50% at the mass scale of 1Msun in the case of weak and strong magnetic field, respectively. By analyzing the torques exerted on fluid elements, we identify the magnetic tension as the dominant process for angular momentum transfer for mass scales < 3Msun for the strong magnetic field case. This critical mass scale can be understood semi-analytically as the timescale of magnetic braking. We show that the anisotropy of the angular momentum transfer due to the presence of strong magnetic field changes the resultant angular momentum of the core only by a factor of two. We also find that the distribution of the angle between the rotation axis and the magnetic field does not show strong alignment even just before the first core formation. Our results also indicate that the variety of the angular momentum of the cores are inherited from the difference of the phase of the initial turbulent velocity field. The variety could contribute to the diversity in size and other properties of protoplanetary disks recently reported by observations.

Young transiting exoplanets offer a unique opportunity to characterize the atmospheres of fresh and evolving products of planet formation. We present the transmission spectrum of V1298 Tau b; a 23 Myr old warm Jovian sized planet orbiting a pre-main sequence star. We detect a primordial atmosphere with an exceptionally large atmospheric scale height and a water vapour absorption at 5$\sigma$ level of significance. We estimate a mass and density upper limit (24$\pm$5$M_{\oplus}$, 0.12gm/$cm^{3}$ respectively). V1298 Tau b is one of the lowest density planets discovered till date. We retrieve a low atmospheric metallicity (logZ=$-0.1^{+0.66}_{-0.72}$ solar), consistent with solar/sub-solar values. Our findings challenge the expected mass-metallicity from core-accretion theory. Our observations can be explained by in-situ formation via pebble accretion together with ongoing evolutionary mechanisms. We do not detect methane, which hints towards a hotter than expected interior from just the formation entropy of this planet. Our observations suggest that V1298 Tau b is likely to evolve into a Neptune/sub-Neptune type of planet.

We report timing and spectral studies of the high mass X-ray binary 4U 1700-37 using Insight-HXMT observations carried out in 2020 during its out-of-eclipse state. We found significant variations in flux on a time-scale of kilo-seconds, while the hardness (count rate ratio between 10-30 keV and 2-10 keV) remains relatively stable. No evident pulsations were found over a frequency range of $10^{-3}$-2000 Hz. During the spectral analysis, for the first time we took the configuration of different Insight-HXMT detectors' orientations into account, which allows us obtaining reliable results even if a stable contamination exists in the field-of-view. We found that the spectrum could be well described by some phenomenological models that commonly used in accreting pulsars (e.g., a power law with a high energy cutoff) in the energy range of 2-100 keV. We found hints of cyclotron absorption features around ~ 16 keV or/and ~ 50 keV.

X-ray binary systems consist of a companion star and a compact object in close orbit. Thanks to their copious X-ray emission, these objects have been studied in detail using X-ray spectroscopy and timing. The inclination of these systems is a major uncertainty in the determination of the mass of the compact object using optical spectroscopic methods. In this paper, we present a new method to constrain the inclination of X-ray binaries, which is based on the modeling of the polarization of X-rays photons produced by a compact source and scattered off the companion star. We describe our method and explore the potential of this technique in the specific case of the low mass X-ray binary GS 1826-238 observed by the Imaging X-ray Polarimetry Explorer (IXPE) observatory.

Supermassive black holes (SMBHs) play an important role in galaxy evolution. Binary and triple SMBHs can form after galaxy mergers. A third SMBH may accelerate the SMBH merging process, possibly through the Kozai mechanism. We use N -body simulations to analyze oscillations in the orbital elements of hierarchical triple SMBHs with surrounding star clusters in galaxy centers. We find that SMBH triples spend only a small fraction of time in the hierarchical merger phase (i.e., a binary SMBH with a distant third SMBH perturber). Most of the time, the enclosed stellar mass within the orbits of the innermost or the outermost SMBH is comparable to the SMBH masses, indicating that the influence of the surrounding stellar population cannot be ignored. We search for Eccentric Kozai-Lidov (EKL) oscillations for which (i) the eccentricity of the inner binary and inclination are both oscillate and are anti-phase or in-phase and (ii) the oscillation period is consistent with EKL timescale. We find that EKL oscillations are short-lived and rare: the triple SMBH spends around 3% of its time in this phase over the ensemble of simulations, reaching around 8% in the best-case scenario. This suggests that the role of the EKL mechanism in accelerating the SMBH merger process may have been overestimated in previous studies. We follow-up with three-body simulations, using initial conditions extracted from the simulation, and the result can to some extent repeat the observed EKL-like oscillations. This comparison provides clues about why those EKL oscillations with perturbing stars are short-lived.

Modal noise appears due to the non-uniform and unstable distribution of light intensity among the finite number of modes in multimode fibres. It is an important limiting factor in measuring radial velocity precisely by fibre-fed high-resolution spectrographs. The problem can become particularly severe as the fibre's core become smaller and the number of modes that can propagate reduces. Thus, mitigating modal noise in relatively small core fibres still remains a challenge. We present here a novel technique to suppress modal noise. Two movable mirrors in the form of a galvanometer reimage the mode-pattern of an input fibre to an output fibre. The mixing of modes coupled to the output fibre can be controlled by the movement of mirrors applying two sinusoidal signals through a voltage generator. We test the technique for four multimode circular fibres: 10 and 50 micron step-index, 50 micron graded-index, and a combination of 50 micron graded-index and 5:1 tapered fibres (GI50t). We present the results of mode suppression both in terms of the direct image of the output fibre and spectrum of white light obtained with the high-resolution spectrograph. We found that the galvanometer mitigated modal noise in all the tested fibres, but was most useful for smaller core fibres. However, there is a trade-off between the modal noise reduction and light-loss. The GI50t provides the best result with about 60% mitigation of modal noise at a cost of about 5% output light-loss. Our solution is easy to use and can be implemented in fibre-fed spectrographs.

I review the use of Type Ia supernovae (SNe Ia) in the 1998 discovery of the accelerating expansion of the Universe, as well as the subsequent use of SNe Ia to study the expansion history in more detail, determine the equation-of-state parameter w, and measure the current value of the Hubble constant. This is the lightly edited transcript of a lecture given at the Standard Model at 50 Symposium held at Case Western University, June 1-4, 2018, and thus corresponds to the state of the field in mid-2018; however, a few post-symposium updates were included in 2019. Also, this version includes at the end a brief update (December 2023) on the early-time vs. late-time Hubble tension, which has now reached a level of 5 sigma based on SNe Ia alone and is supported by several other low-redshift determinations of the Hubble constant.

We propose a mechanism for the excitation of large-scale quasi-periodic fast-propagating magnetoacoustic (QFP) waves observed on both sides of the coronal mass ejection (CME). Through a series of numerical experiments, we successfully simulated the quasi-static evolution of the equilibrium locations of the magnetic flux rope in response to the change of the background magnetic field, as well as the consequent loss of the equilibrium that eventually gives rise to the eruption. During the eruption, we identified QFP waves propagating radially outwards the flux rope, and tracing their origin reveals that they result from the disturbance within the flux rope. Acting as an imperfect waveguide, the flux rope allows the internal disturbance to escape to the outside successively via its surface, invoking the observed QFP waves. Furthermore, we synthesized the images of QFP waves on the basis of the data given by our simulations, and found the consistence with observations. This indicates that the leakage of the disturbance outside the flux rope could be a reasonable mechanism of QFP waves.

(Abridged) Planets are surrounded by fractal surfaces (traditionally called Hill spheres), separating the inner zones of long-term stable orbital motion of their satellites from the outer space where the gravitational pull from the Sun takes over. Through this surface, external minor bodies in trajectories loosely co-orbital to a planet can be stochastically captured by the planet without any assistance from external perturbative forces, and can become moons chaotically orbiting the planet for extended periods of time. Using state-of-the-art orbital integrators, we simulate such capture events for Venus, resulting in long-term attachment phases by reversing the forward integration of a moon initially attached to the planet and escaping it after an extended period of time. Although the probability of a long-term chaotic capture from a single encounter is generally low, the high density of co-orbital bodies in the primordial protoplanetary disk makes this outcome possible, if not probable. The early Venus was surrounded by a dusty gaseous disk of its own, which, coupled with the tidal dissipation of the kinetic energy in the moon and the planet, could shrink the initial orbit and stabilize the captured body within the Hill surface. The tidal torque from the moon, for which we use the historical name Neith, gradually brakes the prograde rotation of Venus, and then reverses it, while the orbit continues to decay. Neith eventually reaches the Roche radius and disintegrates, probably depositing most of its material on Venus' surface. Our calculations show that surface density values of about 0.06 kg m$^{-2}$ for the debris disk may be sufficient to stabilize the initial chaotic orbit of Neith and to bring it down within several radii of Venus, where tidal dissipation becomes more efficient.

We use galaxy-galaxy lensing data to test general relativity and $f(T)$ gravity at galaxies scales. We consider an exact spherically symmetric solution of $f(T)$ theory which is obtained from an approximate quadratic correction, and thus it is expected to hold for every realistic deviation from general relativity. Quantifying the deviation by a single parameter $Q$, and following the post-Newtonian approximation, we obtain the corresponding deviation in the gravitational potential, shear component, and effective surface density (ESD) profile. We used five stellar mass samples and divided them into blue and red to test the model dependence on galaxy color, and we modeled ESD profiles using Navarro-Frenk-White (NFW) profiles. Based on the group catalog from the Sloan Digital Sky Survey Data Release 7 (SDSS DR7) we finally extract $Q=2.138^{+0.952}_{-0.516}\times 10^{-5}\,$Mpc$^{-2}$ at $1\sigma$ confidence. This result indicates that $f(T)$ corrections on top of general relativity are favored. Finally, we apply information criteria, such as the AIC and BIC ones, and although the dependence of $f(T)$ gravity on the off-center effect implies that its optimality needs to be carefully studied, our analysis shows that $f(T)$ gravity is more efficient in fitting the data comparing to general relativity and $\Lambda$CDM paradigm, and thus it offers a challenge to the latter.

The Multipurpose Interferometer Array Pathfinder (MIA), developed from the Argentine Institute of Radio Astronomy (IAR), is a radio astronomical instrument based on interferometry techniques, designed for the detection of radio emission from astronomical sources. Phase one consists of 16 antennas of 5 meters in diameter, with the possibility of increasing their number. In addition, it is equipped with a dual polarization receiver with a bandwidth of 250 MHz, centered at 1325 MHz, and a digitizer and processor for the correlation functions. For the development of this instrument, a three antenna pathfinder is currently being built with its positioning control, radio frequency systems, acquisition and processing stages. This paper will describe the concept design and their current progress for each stage.

To investigate the environment effects on size growth of galaxies, we study the size-mass relation across a broad range of environment with a vast sample of approximately 32 million galaxies at z < 0.5 from the DESI Legacy Imaging Surveys. This sample is divided into 3 subsamples representing galaxies within three different environments: brightest cluster galaxies (BCGs), other cluster galaxies, and field galaxies. The BCGs in our large sample are dominated by quiescent galaxies (QGs), while only a minority (~13%) of BCGs are star-forming galaxies (SFGs). To demonstrate the influence of environment on size growth, we attempt to observe the difference in size-mass relation for these three subsamples. In general, the slope differences between QGs and SFGs within various environments are significant, and tend to be greater at higher redshifts. For the mass-complete subsamples at z < 0.5, BCGs are found to have the highest slope of size-mass relation, and no difference in size-mass relation is found between cluster members and field galaxies. To assess whether the observed slope differences stem from the variations in environment or mass distribution, we construct the mass-matched subsamples for QGs and SFGs. As a result, both QGs and SFGs show negligible difference in slope of size-mass relation among the galaxies within three distinct environments, indicating that stellar mass is the most fundamental factor driving the size evolution at z < 0.5, though the mass growth mode for QGs and SFGs may have been affected by galaxy environment.

These lectures address the effects of Cosmic Rays over macro-instabilities which develop in the interstellar medium and the micro-instabilities the particles are able to trigger themselves. The lectures are centered on the derivation of linear growth rates but also discuss some numerical simulations addressing the issue of magnetic field saturation. A particular emphasis is made on the streaming instability, an instability driven by anisotropic cosmic-ray distributions.

Primordial black holes (PBHs) remain a viable dark matter candidate in the asteroid-mass range. We point out that in this scenario, the PBH abundance would be large enough for at least one object to cross through the inner Solar System per decade. Since Solar System ephemerides are modeled and measured to extremely high precision, such close encounters could produce detectable perturbations to orbital trajectories with characteristic features. We evaluate this possibility with a suite of simple Solar System simulations, and we argue that the abundance of asteroid-mass PBHs can plausibly be probed by existing and near-future data.

We present high-resolution spectra and spectroastrometric (SA) measurements of fundamental rovibrational CO emission from nine nearby ($\lesssim$300 pc) protoplanetary disks where large inner dust cavities have been observed. The emission line profiles and SA signals are fit with a slab disk model that allows the eccentricity of the disk and intensity of the emission to vary as power laws. Six of the sources are well fit with our model, and three of these sources show asymmetric line profiles that can be fit by adopting a non-zero eccentricity. The three other sources have components in either their line profile or SA signal that are not captured by our disk model. Two of these sources (V892 Tau, CQ Tau) have multi-epoch observations that reveal significant variability. CQ Tau and AB Aur have CO line profiles with centrally-peaked components that are similar to line profiles that have been interpreted as evidence of molecular gas arising from a wide-angle disk wind. Alternatively, emission from a circumplanetary disk (CPD) could also account for this component. The interpretations of these results can be clarified in the future with additional epochs that will test the variability timescale of these SA signals. We discuss the utility of using high-resolution spectroscopy for probing the dynamics of gas in the disk and the scenarios that can give rise to profiles that are not fit with a simple disk model.

The spectra of several galaxies, including extremely metal-poor galaxies (EMPGs) from the EMPRESS survey, have shown that the abundances of some Si-group elements differ from "spherical" explosion models of massive stars. This leads to the speculation that these galaxies have experienced supernova explosions with high asphericity, where mixing and fallback of the inner ejecta with the outer material leads to the distinctive chemical compositions. In this article, we consider the jet-driven supernova models by direct two-dimensional hydrodynamics simulations using progenitors about 20 -- 25 $M_{\odot}$ at zero metallicity. We investigate how the abundance patterns depend on the progenitor mass, mass cut and the asphericity of the explosion. We compare the observable with available supernova and galaxy catalogs based on $^{56}$Ni, ejecta mass, and individual element ratios. The proximity of our results with the observational data signifies the importance of aspherical supernova explosions in chemical evolution of these galaxies. Our models will provide the theoretical counterpart for understanding the chemical abundances of high-z galaxies measured by the James Webb Space Telescope.

Multiwavelength observations have revealed that dense, confined circumstellar material (CCSM) commonly exists in the vicinity of supernova (SN) progenitors, suggesting enhanced mass losses years to centuries before their core collapse. Interacting SNe, which are powered or aided by interaction with the CCSM, are considered to be promising high-energy multimessenger transient sources. We present detailed results of broadband electromagnetic emission, following the time-dependent model proposed in the previous work on high-energy SN neutrinos [Murase, Phys. Rev. D 97, 081301(R) (2018)]. We investigate electromagnetic cascades in the presence of Coulomb losses, including inverse-Compton and synchrotron components that significantly contribute to MeV and high-frequency radio bands, respectively. We also discuss the application to SN 2023ixf.

For most writers the science is either an exotic setting or a source of thrilling conflict that would drive the story forward. For a communicator it is the other way around - the science is neatly wrapped in a package of literary tools that make it "invisible" while it remains tangible and most importantly - it can be conveyed to the reader in understandable terms. There are many examples showing how these seemingly contradicting goals can complement each other successfully. I will review how the science was communicated by mainstream and genre writers of yesterday and today, and in different (not necessarily anglophone) cultures. I will bring forward the best and the worst examples that illuminate various astronomical concepts. Finally, I will discuss how we can use them both in outreach and education. Contrary to many similar summaries I will concentrate on some often overlooked mainstream literary examples, including the plays The Physisists by Friedrich D\"urrenmatt and Copenhagen by Michael Frayn, the novel White Garments by Vl. Dudintsev and even an episode of the Inspector Morse TV show, featuring scientists. I will also mention in passing a few less well known genre books.

In this work we consider the realization of a variant emergent Universe scenario in the context of $f(R)$ gravity. We use well-known reconstruction techniques existing in the literature, and we find the approximate form of the vacuum $f(R)$ that reproduces the specific variant emergent Universe scale factor in the large curvature approximation. As we show, in the variant emergent Universe scenario, the Hubble horizon shrinks primordially and the Universe undergoes in an accelerated expansion era. In a perturbation theory approach, the scalar and tensor curvature perturbations can be expressed in terms of the phenomenological indices $\epsilon_i , i=1,3,4$, usually used for inflationary phenomenology, and we extract the spectral indices for the scalar and tensor perturbations, along with the tensor-to-scalar ratio expressed in terms of the perturbation indices. Using a powerful genetic algorithm we investigate in depth the parameter space of the model, quantified by several free parameters, in order to study the viability of the model when this is compared with the Planck 2018 data. We also investigate the implications of the vacuum $f(R)$ gravity we found on the Big Bang nucleosynthesis.

In this paper, we investigate quasinormal modes of scalar and electromagnetic fields in the background of Einstein--scalar--Gauss--Bonnet (EsGB) black holes. Using the scalar and electromagnetic field equations in the vicinity of the EsGB black hole, we study nature of the effective potentials. The dependence of real and imaginary parts of the fundamental quasinormal modes on parameter $p$ (which is related to the Gauss--Bonnet coupling parameter $\alpha$) for different values of multipole numbers $l$ are studied. We analyzed the effects of massive scalar fields on the EsGB black hole, which tells us the existence of quasi--resonances. In the eikonal regime, we find the analytical expression for the quasinormal frequency and show that the correspondence between the eikonal quasinormal modes and null geodesics is valid in the EsGB theory for the test fields. Finally, we study grey-body factors of the electromagnetic fields for different multipole numbers $l$, which deviates from Schwarzschild's black hole.

Neutron stars are known to have strong magnetic fields reaching as high as $10^{15}$ Gauss, besides having strongly curved interior spacetime. So for computing an equation of state for neutron-star matter, the effect of magnetic field as well as curved spacetime should be taken into account. In this article, we compute the equation of state for an ensemble of degenerate fermions in the curved spacetime of a neutron star in presence of a magnetic field. We show that the effect of curved spacetime on the equation of state is relatively stronger than the effect of observed strengths of magnetic field. Besides, a thin layer containing only spin-up neutrons is shown to form at the boundary of a degenerate neutron star.

The GECAM series of satellites utilize LaBr3(Ce), LaBr3(Ce,Sr), and NaI(Tl) crystals as sensitive materials for gamma-ray detectors (GRDs). To investigate the non-linearity in the detection of low-energy gamma rays and address errors in the E-C relationship calibration, comprehensive tests and comparative studies of the non-linearity of these three crystals were conducted using Compton electrons, radioactive sources, and mono-energetic X-rays. The non-linearity test results for Compton electrons and X-rays displayed substantial differences, with all three crystals showing higher non-linearity for X-rays and gamma-rays than for Compton electrons. Despite LaBr3(Ce) and LaBr3(Ce,Sr) crystals having higher absolute light yields, they exhibited a noticeable non-linear decrease in light yield, especially at energies below 400 keV. The NaI(Tl) crystal demonstrated excess light output in the 6~200 keV range, reaching a maximum excess of 9.2% at 30 keV in X-ray testing and up to 15.5% at 14 keV during Compton electron testing, indicating a significant advantage in the detection of low-energy gamma rays. Furthermore, this paper explores the underlying causes of the observed non-linearity in these crystals. This study not only elucidates the detector responses of GECAM, but also marks the inaugural comprehensive investigation into the non-linearity of domestically produced lanthanum bromide and sodium iodide crystals.

The ADMX collaboration gathered data for its Run 1A axion dark matter search from January to June 2017, scanning with an axion haloscope over the frequency range 645-680 MHz (2.66-2.81 ueV in axion mass) at DFSZ sensitivity. The resulting axion search found no axion-like signals comprising all the dark matter in the form of a virialized galactic halo over the entire frequency range, implying lower bound exclusion limits at or below DFSZ coupling at the 90% confidence level. This paper presents expanded details of the axion search analysis of Run 1A, including review of relevant experimental systems, data-taking operations, preparation and interpretation of raw data, axion search methodology, candidate handling, and final axion limits.

In recent years the equations of relativistic first-order viscous hydrodynamics, that is, the relativistic version of Navier-Stokes, have been shown to be well posed and causal under appropriate field redefinitions, also known as hydrodynamic frames. We perform real-time evolutions of these equations for a conformal fluid and explore, quantitatively, the consequences of using different causal frames for different sets of initial data. By defining specific criteria, we make precise and provide evidence for the statement that the arbitrarily chosen frame does not affect the physics up to first order, as long as the system is in the effective field theory regime. Motivated by the physics of the quark-gluon plasma created in heavy-ion collisions we also explore systems which are marginally in the effective field theory regime, finding that even under these circumstances the first order physics is robust under field redefinitions.

Triaxial neutron stars can be sources of continuous gravitational radiation detectable by ground-based interferometers. The amplitude of the emitted gravitational wave can be greatly affected by the state of the hydrodynamical fluid flow inside the neutron star. In this work we examine the most triaxial models along two sequences of constant rest mass, confirming their dynamical stability. We also study the response of a triaxial figure of quasiequilibrium under a variety of perturbations that lead to different fluid flows. Starting from the general relativistic compressible analog of the Newtonian Jacobi ellipsoid, we perform simulations of Dedekind-type flows. We find that in some cases the triaxial neutron star resembles a Riemann-S-type ellipsoid with minor rotation and gravitational wave emission as it evolves towards axisymmetry. The present results highlight the importance of understanding the fluid flow in the interior of a neutron star in terms of its gravitational wave content.

In this work we present a new framework of the gravity sector by considering the extension $F(R,w)$, in which $R$ is the Ricci scalar and $w$ is the equation of state. Three different choices of function $F(R,w)$ are investigated under the Palatini formalism. The models appear equivalent to $F(R)$ models of gravity with effective momentum-energy tensors. For linear dependence of Ricci scalar in which $F(R,w)=k(w)R$, the model appears equivalent to Einstein-Hilbert action with effective momentum-energy tensor. Recovering the minimal coupling case of the last choice does not face Jordan-Einstein frame ambiguities and exhibits natural alignments with general relativity results in the matter\text{/} radiation dominated eras. We discuss some astrophysical implications of the model by considering scalar fields as dominant matter forms. We show that the Higgs inflation could be saved within the $F(R,w)$ model. We suggest some future investigations exemplified by constant-roll inflation and universe evolution for $F(R)=f(R)k(w)$ where $f(R)$ represents the Starobinsky gravitational form. Using the model and comparing it with pure $F(R)$ gravity, we provide preliminary indications of $F(R,w)$'s impact. As a final note, we suggest using the Polytropic equation of state in future works to investigate $F(R,w)$.

We thoroughly explore the cosmic gravitational focusing of cosmic neutrino fluid (C$\nu$F) by dark matter (DM) halo using both general relativity for a point source of gravitational potential and Boltzmann equations for continuous overdensities. Derived in the most general way for both relativistic and non-relativistic neutrinos, our results show that the effect has fourth power dependence on the neutrino mass and temperature. With nonlinear mass dependence which is different from the cosmic microwave background (CMB) and large scale structure (LSS) observations, the cosmic gravitational focusing can provide an independent cosmological way of measuring the neutrino mass and ordering. We take DESI as an example to illustrate that the projected sensitivity as well as its synergy with existing terrestrial neutrino oscillation experiments and other cosmological observations can significantly improve the neutrino mass measurement.

We investigate the effects of an early cosmological period, dominated by primordial 2-2-holes, on axion dark matter. 2-2-holes emerge in quadratic gravity, a candidate theory of quantum gravity, as a new family of classical solutions for ultracompact matter distributions. These objects have the black hole exterior without an event horizon and hence, as a probable endpoint of gravitational collapse, they do not suffer from the information loss problem. Thermal 2-2-holes exhibit Hawking-like classical radiation and satisfy the entropy-area law. Moreover, these objects, unlike BHs, have a minimum allowed mass and hence naturally give rise to stable remnants. In this paper, we consider the remnant contribution to dark matter (DM) small and adopt the axion DM scenario by the misalignment mechanism. We show that a 2-2-hole domination phase in the evolution of the universe changes the axion mass window from the dark matter abundance constraints. The biggest effect occurs when the remnants have the Planck mass, which is the case for a strongly coupled quantum gravity. The change in abundance constraints for the Planck mass 2-2-hole remnants amounts to that of the Primordial Black Hole (PBH) counterpart. Therefore; since we use the revised constraints on the initial fraction of 2-2-holes from GWs, the results here can also be considered as the updated version of the PBH case. As a result, the lower limit on the axion mass is found as $m_a \sim 10^{-9}$ eV. Furthermore, the domination scenario itself constrains the remnant mass $M_{\mathrm{min}}$ considerably. Given that we focus on the pre-BBN domination scenario in order not to interfere with BBN (Big Bang Nucleosynthesis) constraints, the remnant mass window becomes $m_{\mathrm{Pl}} \lesssim M_{\mathrm{min}} \lesssim 0.1\;\mathrm{g}$.

Large uncertainties in the determinations of the equation of state of dense stellar matter allow the intriguing possibility that the bulk quark matter in beta equilibrium might be the true ground state of the matter at zero pressure. And quarks will form Cooper pairs very readily since the dominant interaction between quarks is attractive in some channels. As a result, quark matter will generically exhibit color superconductivity, with the favored pairing pattern at intermediately high densities being two-flavor pairing. In the light of several possible candidates for such self-bound quark stars, including the very low-mass central compact object in supernova remnant HESS J1731-347 reported recently, we carry out one field-theoretic model, the Nambu-Jona-Lasinio model, of investigation on the stability of beta-stable two-flavor color superconducting (2SC) phase of quark matter, nevertheless find no physically-allowed parameter space for the existence of 2SC quark stars.

It is important to develop a unified theoretical framework to describe the nuclear experiments and astrophysical observations based on the same effective nuclear interactions. Based on the so-called Skyrme pseudopotential up to next-to-next-to-next-to-leading order, we construct a series of extended Skyrme interactions by modifying the density-dependent term and fitting the empirical nucleon optical potential up to above $1$ GeV, the empirical properties of isospin symmetric nuclear matter, the microscopic calculations of pure neutron matter and the properties of neutron stars from astrophysical observations. The modification of the density-dependent term in the extended Skyrme interactions follows the idea of Fermi momentum expansion and this leads to a highly flexible density behavior of the symmetry energy. In particular, the values of the density slope parameter $L$ of the symmetry energy for the new extended Skyrme interactions range from $L = -5$ MeV to $L = 125$ MeV by construction, to cover the large uncertainty of the density dependence of the symmetry energy. Furthermore, in order to consider the effects of isoscalar and isovector nucleon effective masses, we adjust the momentum dependency of the single-nucleon optical potential and the symmetry potential of these new extended Skyrme interactions and construct a parameter set family, by which we systematically study the impacts of the symmetry energy and the nucleon effective masses on the properties of nuclear matter and neutron stars. The new extended Skyrme interactions constructed in the present work will be useful to determine the equation of state of isospin asymmetric nuclear matter, especially the symmetry energy, as well as the nucleon effective masses and their isospin splitting, in transport model simulations for heavy-ion collisions, nuclear structure calculations and neutron star studies.

We further investigate novel features of the $T-$vacuum state, originally defined in the context of quantum field theory in a (1+1) dimensional radiation dominated universe [Modak, JHEP 12, 031 (2020)]. Here we extend the previous work to a realistic (3+1) dimensional set up and show that $T-$vacuum causes an \emph{anisotropic particle creation} in the radiation dominated early universe. Unlike the Hawking or Unruh effect, where the particle content is thermal and asymptotically defined, here it is non-thermal and time dependent. This novel example of particle creation is interesting because these particles are detected in the frame of physical/cosmological observers, who envision the $T-$vacuum as a particle excited state, and therefore may eventually be compared with observations.

Neutrinos are often considered as a portal to new physics beyond the Standard Model (SM) and might possess phenomenologically interesting interactions with dark matter (DM). This paper examines the cosmological imprints of DM that interacts with and is produced from SM neutrinos at temperatures below the MeV scale. We take a model-independent approach to compute the evolution of DM in this framework and present analytic results which agree well with numerical ones. Both freeze-in and freeze-out regimes are included in our analysis. Furthermore, we demonstrate that the thermal evolution of neutrinos might be substantially affected by their interaction with DM. We highlight two distinctive imprints of such DM on neutrinos: (i) a large, negative contribution to $N_{\rm eff}$, which is close to the current experimental limits and will readily be probed by future experiments; (ii) spectral distortion of the cosmic neutrino background (C$\nu$B) due to DM annihilating into neutrinos, a potentially important effect for the ongoing experimental efforts to detect C$\nu$B.

We study finite-coupling effects of QFT on a rigid de Sitter (dS) background taking the $O(N)$ vector model at large $N$ as a solvable example. Extending standard large $N$ techniques to the dS background, we analyze the phase structure and late-time four-point functions. Explicit computations reveal that the spontaneous breaking of continuous symmetries is prohibited due to strong IR effects, akin to flat two-dimensional space. Resumming loop diagrams, we compute the late-time four-point functions of vector fields at large $N$, demonstrating that their spectral density is meromorphic in the spectral plane and positive along the principal series. These results offer highly nontrivial checks of unitarity and analyticity for cosmological correlators.

Theories in which the dark matter (DM) candidate is a fermion transforming chirally under a gauge symmetry are attractive, as the gauge symmetry would protect the DM mass. In such theories, the universe would have undergone a phase transition at early times that generated the DM mass upon spontaneous breaking of the gauge symmetry. In this paper, we explore the gravitational wave signals of a simple such theory based on an $\mathrm{SU}(2)_\mathrm{D}$ dark sector with a dark isospin-$3/2$ fermion serving as the DM candidate. This is arguably the simplest chiral theory possible. The scalar sector consists of a dark isospin-$3$ multiplet which breaks the $\mathrm{SU}(2)_\mathrm{D}$ gauge symmetry and also generates the DM mass. We construct the full thermal potential of the model and identify regions of parameter space which lead to detectable gravitational wave signals, arising from a strong first-order $\mathrm{SU}(2)_\mathrm{D}$ phase transition, in various planned space-based interferometers, while also being consistent with dark matter relic abundance. Bulk of the parameter space exhibiting detectable gravitational wave signals in the model also has large WIMP-nucleon scattering cross sections, $\sigma_{\rm SI}$, which could be probed in upcoming direct detection experiments.

We study thermal corrections to a model of real scalar dark matter interacting feebly with a SM fermion and a gauge-charged vector-like fermion. We employ the Closed-Time-Path (CTP) formalism for our calculation and go beyond previous works by including the full dependence on the relevant mass scales as opposed to using (non)relativistic approximations. In particular, we use 1PI-resummed propagators without relying on the Hard-Thermal-Loop approximation. We conduct our analysis at leading order in the loop expansion of the 2PI effective action and compare our findings to commonly used approximation schemes, including the aforementioned Hard-Thermal-Loop approximation and results obtained from solving Boltzmann equations using thermal masses as a regulator for $t$-channel divergences. We find that the Boltzmann approach deviates between $-10\%$ and $+30\%$ from our calculation, where the size and sign strongly depends on the mass splitting between the DM candidate and the gauge-charged parent. The HTL-approximated result is more precise for small gauge couplings and is percent level accurate for large mass splittings, whereas it overestimates the relic density up to $25 \%$ for small mass splittings. Tree-level propagators lead to underabundant DM as they do not account for scattering contributions and can deviate up to $-100\%$ from the 1PI-resummed result.