The future space based gravitational wave detector Laser Interferometer Space Antenna will observe millions of Galactic binaries constantly present in the data stream. A small fraction of this population (of the order of several thousand) will be individually resolved. One of the challenging tasks from the data analysis point of view will be to estimate the parameters of resolvable galactic binaries while disentangling them from each other and from other gravitational wave sources present in the data. This problem is quite often referred to as a global fit in the field of Laser Interferometer Space Antenna data analysis. A Bayesian framework is often used to infer the parameters of the sources and their number. The efficiency of the sampling techniques strongly depends on the proposals, especially in the multidimensional parameter space. In this paper we demonstrate how we can use neural density estimators, and in particular normalizing flows, in order to build proposals which significantly improve the convergence of sampling. We also demonstrate how these methods could help in building priors based on physical models and provide an alternative way to represent the catalog of identified gravitational wave sources.

We construct the first-order perturbative Taub-Newman-Unti-Tamburino (Taub-NUT) black hole solutions in Einstein gravity extended with a cubic curvature invariant. The corrected thermodynamic quantities are then obtained by the standard method and the first law and Smarr relation are satisfied. We also study the perturbative correction to thermodynamics using the Reall-Santos (RS) method and verify that the method is still applicable even though the metrics are no longer asymptotic to Minkowski spacetime. We then apply the RS method to obtain the leading correction to the thermodynamics of the complicated Kerr-Taub-NUT black holes.

To understand the nature of the black holes that exist in the Universe, it is also necessary to study what happens to the (quantum) matter that collapses and forms such objects. In this work, we consider a dust ball with an electrically charged central core and study its quantum spectrum by quantizing the geodesic equation for individual dust particles in the corresponding Reissner-Nordström spacetime. As in the neutral case investigated previously, we find a ground state of the dust ball with the size of a fraction of the outer horizon. Moreover, we determine a self-consistent configuration of layers in the ground state corresponding to an effective mass function that increases linearly with the areal radius and has no inner Cauchy horizon. We then briefly speculate on the possible phenomenological consequences for the endpoint of the gravitational collapse.

The Tolman–Ehrenfest criterion of thermal equilibrium for a static fluid in a static spacetime is generalized to stationary heat conduction, in the approximation in which backreaction is negligible. Applying this generalized criterion to the Hawking radiation in the Schwarzschild–de Sitter geometry shows that the two horizons (which act as thermostats) remain in thermal equilibrium. The temperature of the radiation fluid interpolates between the temperatures at the horizons, with a static analytic profile that is given explicitly.

The interaction between waves and matter in the Universe is a fundamental but very challenging problem, since one needs to consistently solve the Einstein-matter equations in a dynamical regime. To shed some light on this problem, we investigate the transmission of scalar, electromagnetic, and linearized odd-parity gravitational waves in a toy model. This model consists of a static spacetime satisfying Einstein’s field equations which is characterized by a spherical distribution of matter in the form of thin concentric equidistant shells of equal mass which is perturbed by a linear wave. More specifically, we assume that the central region has zero mass, and we verify that the resulting spacetime is stable with respect to small perturbations of the shell radii as long as the gravitational field is sufficiently weak. We focus on the transmission of monochromatic waves emitted from the center and propagating through a succession of $N$ shells. Analytical expressions for the transmission and reflection coefficients are obtained and their dependency on the frequency, the number of shells and their mutual distance is analyzed. In particular, in the high-frequency limit, we observe that the reflection coefficient decays with the fourth power of the frequency. Increasing the number of shells initially produces oscillations in the transmission coefficient; however, as $N$ grows, this coefficient rapidly stabilizes at a constant positive value. We attribute this property to the fact that reflections are mainly determined by the surface density of the shells, which decreases as the inverse square of their radii.

A Gibbons-Maeda-Garfinkle-Horowitz-Strominger (GMGHS) black hole with a magnetic charge (or an electric charge) has noteworthy features that its scalar curvature near the event horizon of the black hole with the almost maximal charge can be extremely large. The large curvature, which is related with the gravity on a finite-sized object or between two points, causes high center-of-mass energy for two neutral particles near the almost maximally charged GMGHS black hole. Recently, the Event Horizon Telescope Collaboration gave the bound on the charge of black holes from the shadow and mass observations of black holes under an assumption that the diameter of observed rings are proportion to that of photon spheres. The photon sphere would be less related with the curvature, since it is determined by the behavior of one photon or one ray neither two photons nor two rays. Thus, the high-energy neutral particle collision and the black hole shadow observations would be complementary to distinguish the GMGHS black hole from other black hole solutions. In this paper, we investigate a new way to compare the center-of-mass energy for neutral particle collisions in the GMGHS spacetime and other black hole spacetimes. From the shadow observations and the mass observations under the assumptions on the effect of black hole charges, we can put constraints on the center-of-mass energy of the particles. We apply our method to shadow and mass observations of M87* and Sagittarius A*. We find that the center-of-mass energy of neutral particles near the GMGHS black holes cannot be extremely large under the observational constraints, and conclude that the GMGHS spacetimes are hardly distinguishable from the Reissner-Nordström spacetimes by the particle collisions if we apply the shadow and mass observations at $1\sigma$ probability.

Previous work has shown that the interaction between gravitational waves (GWs) and a shell of viscous matter leads to damping of the GWs and heating of the matter, and that these effects may be astrophysically significant. This result was derived using the theory of linear perturbations about a Minkowki background, and in this work the model is extended to be more physically realistic by allowing the background geometry to be Schwarzschild. It is found that the difference between using a Schwarzschild or Minkowski background is minimal when either $r\gg M$ or $\lambda <M$, where $r$ is the radius of the shell, $\lambda$ is the GW wavelength and $M$ is the mass of the system in geometric units (so that $1M_{\odot }=1.48\mathrm{km}$). However, when $r\sim 6M$ and $\lambda \sim 25M$, then the damping and heating effects are about 9 times larger on a Schwarzschild background than on Minkowski, and such situations occur astrophysically.

The field equations of general relativity can be derived from the Einstein action, which is quadratic in connection coefficients, rather than the standard action involving the Gibbons-Hawking-York term and counterterm. We show that it is possible to construct a new counterterm directly for the Einstein action, which removes divergences and naturally introduces a flat reference spacetime. The total action is then covariant under simultaneous transformation of both the spacetime and reference tetrads, and we argue that this is analogous to the Gibbons-Hawking action. We then explore different perspectives arising naturally from different uses of the reference tetrad and explore implications of viewing gravity as fundamentally described in terms of noncovariant connection coefficients.

We present a new class of models that have the potential to alleviate tensions present in the cosmological data today. We postulate about variation in the sound horizon scale on superhorizon scales, i.e., on scales that are larger than that of the present observable low-redshift Universe ($\gtrsim 1\mathrm{Gpc}$) while at the same time smaller than the largest scales probed by the cosmic microwave background (CMB) ($\lesssim 10\mathrm{Gpc}$). In this scenario, CMB peaks are naturally smoothed as preferred by the Planck data, while at the same time the low-redshift baryon acoustic oscillation calibration is partially decoupled from the CMB. Taking superhorizon variations in baryon fraction as an example and using approximate modeling, we find improvement in the best fit Planck power spectrum model $\mathrm{\Delta }{\chi }^2\sim 6$ for 1 extra degree of freedom with the relevant extension parameter ${10}^3{\sigma }_b=2.10\pm 0.60$, implying about 10% variations in baryon fraction across the Universe. At the same time, $S_8$ drops by about 1 sigma, easing tension with weak lensing surveys. We find that the combination of Planck 2018 data, eBOSS BAO data, and Riess et al. distance ladder Hubble parameter determination produce a satisfactory fit in our model if we allow for a phantom dark energy equation of state.

Using an optimal quadratic estimator, we measure the large-scale cross-correlation between maps of the stochastic gravitational-wave intensity, constructed from the first three LIGO-Virgo observing runs, and a suite of tomographic samples of galaxies covering the redshift range $z\lesssim 2$. We do not detect any statistically significant cross-correlation, but the tomographic nature of the data allows us to place constraints on the (bias-weighted) production rate density of gravitational waves by astrophysical sources as a function of cosmic time. Our constraints range from $⟨b{\dot{\mathrm{\Omega }}}_{\mathrm{GW}}⟩<3.0\times {10}^{-9}{\mathrm{Gyr}}^{-1}$ at $z\sim 0.06$ to $⟨b{\dot{\mathrm{\Omega }}}_{\mathrm{GW}}⟩<2.7\times {10}^{-7}{\mathrm{Gyr}}^{-1}$ at $z\sim 1.5$ (95% confidence level), assuming a frequency spectrum of the form $f^{2/3}$ (corresponding to an astrophysical background of binary mergers), and a reference frequency $f_{\mathrm{ref}}=25\mathrm{Hz}$. Although these constraints are $\sim 2$ orders of magnitude higher than the expected signal, we show that a detection may be possible with future experiments.

This paper presents the results of a systematic study of projection biases in the weak lensing analysis of cosmic shear and the combination of galaxy clustering and galaxy-galaxy lensing using data collected during the first year of running the Dark Energy Survey experiment. The study uses Lambda cold dark matter ($\mathrm{\Lambda }\text{CDM}$) as the cosmological model and two-point correlation functions for the weak lensing (WL) analysis. The results in this paper show that, independent of the WL analysis, projection biases of more than $1\sigma$ exist and are a function of the position of the true values of the parameters $h$, $n_s$, ${\mathrm{\Omega }}_b$, and ${\mathrm{\Omega }}_{\nu }{h}^2$ with respect to their prior probabilities. For cosmic shear, and the combination of galaxy clustering and galaxy-galaxy lensing, this study shows that the coverage probability of the 68.27% credible intervals ranges from as high as 93% to as low as 16% and that these credible intervals are inflated, on average, by 29% for cosmic shear and 20% for the combination of galaxy clustering and galaxy-galaxy lensing. The results of the study also show that, in six out of nine tested cases, the reduction in error bars obtained by transforming credible intervals into confidence intervals is equivalent to an increase in the amount of data by a factor of 3.

The remnant black hole from a binary coalescence emits ringdown gravitational waves characterized by quasinormal modes, which depend solely on the remnant’s mass and spin. In contrast, the ringdown amplitudes and phases are determined by the properties of the merging progenitors. Accurately modeling these amplitudes and phases reduces systematic biases in parameter estimation and enables the development and performance of rigorous tests of general relativity. We present a state-of-the-art, data-driven surrogate model for ringdown amplitudes and phases, leveraging Gaussian process regression trained against sxs numerical-relativity simulations. Focusing on nonprecessing, quasicircular binary black holes, our model offers the most comprehensive fit that includes 16 emission modes, incorporating overtones and quadratic contributions. Our surrogate model achieves reconstruction errors that are approximately 2 orders of magnitude smaller than the typical measurement errors of current gravitational-wave interferometers. An additional benefit of our approach is its flexibility, which allows for future extensions to include features such as eccentricity and precession, broadening the scope of its applicability to more generic astrophysical scenarios. Finally, we are releasing our model in a ready-to-use package called postmerger.

For high-energy cosmic-ray physics, it is imperative to determine the mass and energy of the cosmic ray that initiated the air shower in the atmosphere. This information can be extracted from the longitudinal profile of the air shower. In radio-metric observations, this profile is customarily determined through an extensive fitting procedure where calculated radio intensity is fitted to data. Beamforming the measured signals offers a promising alternative to bypass the cumbersome fitting procedure and to determine the longitudinal profile directly. Finite aperture effects in beamforming hamper the resolution with which this profile can be determined. We present a comprehensive investigation of the beamforming resolution in radiometric observations of air showers. There are two, principally different, approaches possible in air-shower beamforming, one where the total beamforming intensity is determined and an alternative where the beamforming trace is cross-correlated with a known response function. The effects due to a finite aperture (size of antenna array and bandwidth) are large for both approaches. We argue that it is possible to correct for the aperture corrections using an unfolding procedure. We give an explicit expression for the folding function, the kernel. Being able to calculate the folding function allows for unfolding the finite aperture effects from the data. We show that, in a model-to-model comparison, this allows for an accurate reconstruction of the current profile as the shower develops in the atmosphere. We present also an example where we reconstruct the longitudinal current profile of a shower developing under thunderstorm conditions where the atmospheric electric fields greatly alter the orientation of the transverse current in the shower front.

The all-particle spectrum of cosmic rays measured at Earth has a kneelike feature around 4 PeV. A priori, it is not clear if this is a local feature specific to the Solar neighborhood in the Milky Way or if it is a generic property of the Galactic cosmic-ray spectrum. We argue that combining gamma-ray and cosmic-ray data of Large High Altitude Air Shower Observatory (LHAASO) indicates that the knee is a local feature. In order to demonstrate this, we derive a model for the local cosmic-ray spectrum and composition, consistent with the recent LHAASO measurements of the all-particle spectrum and the mean logarithmic mass in the knee region. We calculate the spectrum of diffuse gamma-ray emission based on this model and find that the expected spectral shape of the diffuse gamma-ray flux disagrees with the LHAASO measurements of the diffuse gamma-ray emission in the 10–100 TeV energy range in the inner and outer Galaxy. We determine the break energy in the cosmic-ray spectrum expected from these gamma-ray data and find it an energy 10 times lower than obtained from local measurements.

In the detection of gravitational waves in space, during the science phase of the mission, the point ahead angle mechanism (PAAM) serves to steer a laser beam to compensate for the angle generated by the relative motion of the two spacecrafts (SCs) during the approximately 10 seconds of flight time a laser beam will take from one SC to reach a distant SC of three million kilometers away. The common practice for pointing stability control of a laser beam is to first do a coarse tracking by the PAAM to steer a laser beam to compensate for the relative motion between two SCs and to be followed by a fine pointing stability control. In the present work, by exploiting the near-circular orbit structure of an individual SC in the triangular constellation, the feasibility of inserting an adaptive extended Kalman filter (AEKF) into the PAAM control loop is investigated. By adopting a colored measurement noise model that closely resembles the prospective on an orbit situation, numerical simulation suggests that the dynamic range of the PAAM may be reduced to the level of nanoradians using the prediction of the pointing head angle by the AEKF. This will cut down on the tilt-to-length (TTL) coupling noise and the position noise budget allocated to the PAAM. This in turn reduces the dynamic range of the fine pointing control and leaves room to improve its accuracy, thereby offering the prospect of reduction of the position noise budget allocated to the laser pointing instability as a whole.

A hybrid framework of spin hydrodynamics is proposed that combines the results of kinetic theory for particles with spin $1/2$ with the Israel-Stewart method of introducing nonequilibrium dynamics. The framework of kinetic theory is used to define the perfect-fluid description that conserves baryon number, energy, linear momentum and spin part of angular momentum. This leads to the entropy conservation although, in the presence of spin degrees of freedom, the perfect-fluid formalism includes extra terms whose structure is usually attributed to dissipation. The genuine dissipative terms appear from the condition of positive entropy production in nonequilibrium processes. They are responsible for the transfer between the spin and orbital parts of angular momentum, with the total angular momentum being conserved.

Cosmic ray (CR) upscattering of dark matter is considered as one of the most straightforward mechanisms to accelerate ambient dark matter, making it detectable at high threshold, large volume experiments. In this work, we revisit CR upscattered dark matter signals at the IceCube detector, focusing on lower energy data than was considered before. We consider both scattering with electrons and nuclei. In the latter, we include both elastic and deep-inelastic scattering computations. As concrete examples, we consider two benchmark models; fermion dark matter with vector and scalar mediators. We compare our model projections with the most current constraints and show that the IceCube detector can detect CR-boosted dark matter especially with masses below $\sim 100\mathrm{keV}$ when scattering with electrons and $\sim \mathrm{MeV}$ in the nucleon scattering case.

Curiously, in the minimal left right symmetric model chiral symmetry that protects the electron’s mass ($m_e$), due to parity ($P$), implies in the symmetry limit the vanishing of its neutrino mixing angles. We break the chiral symmetry softly (or spontaneously if it is gauged) to generate the observed large neutrino mixing angles at the tree-level. The electron then acquires its mass on renormalization group equation (RGE) running due to its neutrino’s mixing, and in turn determines the $B-L$ gauge symmetry breaking scale ($v_R$) to be ${10}^{10}\mathrm{GeV}\lesssim v_R\le {10}^{15}\mathrm{GeV}$. If the muon’s mass is also generated radiatively, the $B-L$ breaking scale is $\sim {10}^{14-15}\mathrm{GeV}$. Regardless of the high scale of $v_R$, this is a testable model since on RGE running and $P$ breaking, a large strong $CP$ phase ($\overline{\theta }\gg {10}^{-10}$) which depends logarithmically on $v_R$ is generated if there is $\mathcal{O}(1)$ $CP$ violation in leptonic Yukawa couplings. Hence we expect that leptonic $CP$ phases including the Dirac $CP$ phase ${\delta }_{CP}$ of the PMNS matrix must be consistent with 0 or ${180}^o$ to within a degree, which can be verified or excluded by neutrino experiments such as DUNE and Hyper-Kamiokande. In lieu of $P$, if charge conjugation $C$ is used, the same results follow. However with $C$ and no $P$, axions would likely need to be added anyway, in which case there is no constraint on ${\delta }_{CP}$.

After the first observation of coherent elastic neutrino-nucleus scattering ($\mathrm{CE}\nu \mathrm{NS}$) by the COHERENT Collaboration, many efforts are being made to improve the measurement of this process, making it possible to constrain new physics in the neutrino sector. In this paper, we study the sensitivity to non-standard interactions (NSIs) and generalized neutrino interactions of two experimental setups at the Spallation Neutron Source at Oak Ridge National Laboratory: a NaI detector with characteristics similar to the one that is currently being deployed there and a cryogenic CsI detector proposed at the same facility. We show that a combined analysis of the data from these detectors, whose target nuclei have significantly different proton-to-neutron ratios, could help to partially break the parameter degeneracies arising from the interference between the Standard Model and NSI contributions to the $\mathrm{CE}\nu \mathrm{NS}$ cross section, as well as between different NSI parameters. By contrast, only a slight improvement over the current CsI constraints is expected for parameters that do not interfere with the SM contribution.

The baryon masses on Coordinate Lattice Simulations (CLS) ensembles are used to determine the Low-Energy Constants (LEC) that characterize quantum chromodynamics in the flavor-SU(3) limit with vanishing up, down, and strange quark masses. Here we reevaluate some of the baryon masses on flavor-symmetric ensembles with much-improved statistical precision, in particular for the decuplet states. These additional results then lead to a more significant chiral extrapolation of the lattice dataset to its chiral SU(3) limit. Our results are based on the chiral Lagrangian with baryon octet and decuplet fields considered at the one-loop level. Finite-box and discretization effects of the lattice data are considered systematically. While in our global fit of the data we insist on large-$N_c$ sum rules for the LEC that enter at ${\mathrm{N}}^3\mathrm{LO}$, all other LEC are unconstrained. In particular, we obtain values for the chiral limit of the pion decay constant and the isospin-limit of the quark-mass ratio compatible with the FLAG report.