We consider diffeomorphism invariant theories of gravity with arbitrary higher derivative corrections to the two derivative Einstein’s theory in the presence of Proca fields—vector fields without $U(1)$ gauge invariance. We prove that, in such theories, the surface gravity remains constant across the Killing horizon of stationary black hole solutions, without requiring the existence of a bifurcation surface. Our analysis is carried out within an effective field theory framework, where higher derivative contributions are treated perturbatively around the two derivative theory. The proof relies on specific components of the coupled gravity—Proca field equations together with constraints implied by the near horizon boost symmetry of stationary black hole geometries, analyzed using boost-weight arguments. Implementing these arguments in the presence of Proca fields introduces new subtleties beyond those encountered in the pure gravity case. We provide a systematic resolution of these subtleties and demonstrate that the surface gravity remains constant to all orders in the perturbative expansion, thereby establishing the zeroth law. Finally, we outline how this framework can be generalized to broader classes of vector theories with four propagating degrees of freedom, which exhibit qualitative differences from both the Proca and gauge invariant vector theories.

This work digs into the connection between gravity and thermodynamics of stretched light cones (SLC). They are associated with uniformly accelerating observers, who endow the SLC with a physical notion of temperature via the Unruh effect. We compute the expansion, shear, and vorticity of the SLC to fully study its dynamics and account for the possibility of previously predicted nonequilibrium entropy production. For consistency, we prove the equivalence of the two different geometrical methods available for studying the SLCs’ properties. Then, we apply the energy balance and use Clausius’ relation to relate the geometrical properties of the SLC with energy fluxes crossing its surface, showing that it encodes the equations governing the gravitational dynamics. We show here how this analysis can be fully carried in terms of equilibrium thermodynamics due to the vanishing of shear, and how one can identify a work term related to the acceleration of the observer.

The black hole shadow is fundamentally connected to the structure of light rings and the photon region in the background geometry. We investigate the photon region boundary in a generic asymptotically flat, stationary, axisymmetric black hole spacetime that admits spherical photon orbits (SPOs). Explicit expressions possessing real solutions are provided for the photon regions boundary purely in terms of the background metric functions, independent of the photons parameters like energy or angular momentum, which are applicable to both separable and nonseparable spacetimes. We further analyze its common features, including overlap with the ergoregion and rotation sense of SPOs. Additionally, light rings are identified at the extrema of the photon region boundary curves in the $(r,\theta )$ plane. Our approach is validated against a few exact black hole solutions. Implications are discussed.

In this paper, we identify a novel topological subclass, dubbed ${\tilde{W}}^{1+}$, in the thermodynamics of higher odd-dimensional, multiply rotating Kerr anti–de Sitter (AdS) black holes. This discovery extends the established topological classification beyond the five classes and two subclasses previously known. The ${\tilde{W}}^{1+}$ subclass exhibits a unique and previously unreported stability profile: it admits a thermodynamically stable small black hole state in the low-temperature limit, while in the high-temperature limit, the phase space simultaneously contains one stable large black hole, one stable small black hole, and one unstable small black hole state. Our analysis, which treats black hole solutions as topological defects, reveals a richer landscape of black hole thermodynamics than previously understood and necessitates an expansion of the topological classification scheme to accommodate this new phenomenology.

We present the population properties of binary black hole mergers identified by the ias-hm pipeline (which incorporates higher-order modes in the search templates) during the third observing run (O3) of the LIGO, Virgo, and KAGRA (LVK) detectors. In our population inference analysis, instead of only using events above a sharp cut based on a particular detection threshold (e.g., false alarm rate), we use a Bayesian framework to consistently include both marginal and confident events. We find that our inference based solely on highly significant events ($p_{\text{astro}}\sim 1$) is broadly consistent with the GWTC-3 population analysis performed by the LVK Collaboration. However, incorporating marginal events into the analysis leads to a preference for stronger redshift evolution in the merger rate and an increased density of asymmetric mass-ratio mergers relative to the GWTC-3 analysis, while remaining within its allowed parameter ranges. Using simple parametric models to describe the binary black hole population, we estimate a merger rate density [$R(z)={\mathcal{R}}_0(1+z{)}^{\kappa }$] of ${32.4}_{-12.2}^{+18.5}{\mathrm{Gpc}}^{-3}{\mathrm{yr}}^{-1}$ at redshift $z=0.2$ and a redshift evolution parameter of $\kappa ={4.4}_{-2.0}^{+1.9}$. Assuming a power-law form for the mass-ratio distribution ($\propto q^{\beta }$), we infer $\beta ={0.1}_{-1.4}^{+1.9}$, indicating a relatively flat distribution. These results highlight the potential impact of marginal events on population inferences and motivate future analyses with data from upcoming observing runs.

We study the linear perturbations of a spherically symmetric black hole corrected by dimension-6 terms in the effective field theory (EFT) of gravity. The solution is asymptotically flat and characterized by two parameters—a mass parameter $M$ and a dimensionless parameter $ϵ$ related to the EFT length scale $l$, and the perturbation equation incorporates a velocity factor which is not constant. The quasinormal modes (QNMs) and time-domain waveforms are studied within the hyperboloidal framework. This approach reproduces the breakdown of the isospectrality and reveals that higher overtones are more sensitive to $ϵ$. As for the time domain, the mismatch function is introduced and found to scale as ${ϵ}^2$, which demonstrates that the waveform is stable as $ϵ$ varies. Finally, a velocity-dependent energy norm is employed to compute the pseudospectrum and characterize the migration of the QNM spectrum. We further define a quantity ${\epsilon }_c$ that describes the magnitude of the instability of a QNM spectrum. Our analysis reveals that the dependence of ${\epsilon }_c$ on $ϵ$ is complicated—it may increase, decrease or even be nonmonotonic.

The tidal deformability is a key observable to test the nature of compact objects in a binary coalescence. Within vacuum general relativity, the tidal Love numbers of a four-dimensional black hole are strictly zero, while they are nonzero and model-dependent for material objects, matter distributions around black holes, or in alternative theories of gravity. Here, we develop a model-agnostic framework based on the membrane paradigm, where the tidal properties of a spherically symmetric object are encoded in the response of a fictitious membrane in terms of viscosity coefficients. We show that both neutron stars and exotic compact objects (in particular, we provide an explicit example for thin-shell gravastars) are included in this framework, provided that the bulk and shear viscosity coefficients of the membrane have a nontrivial frequency dependence. We derive a general result for the electric and magnetic tidal Love numbers for nonrotating and spherically symmetric compact objects in terms of the viscosity coefficients, discussing their behavior with the compactness of the object, and identifying the conditions for the logarithmic behavior found in previous literature for various ultracompact objects. Finally, we show that the membrane shear viscosity coefficients associated with neutron star models feature novel quasiuniversal relations, which depend only mildly on the neutron-star equation of state.

Quantum correlations across the horizon could be pivotal in resolving the puzzles surrounding the quantum aspects of black holes and the Hawking radiation. The peaks in the equal time correlation function are typically attributed to entangled particle excitations. In this work, we have investigated the evolution of correlations of a test quantum field on a dynamical background spacetime undergoing a gravitational collapse. In the case of a supercritical collapse, as the black hole and its horizon forms, correlated peaks are seen to appear across the horizon, representing an entangled Hawking pair. The outside peak moves away from the horizon as the system evolves, possibly representing outgoing Hawking flux. Implications of these nonlocal correlations are discussed in the light of the information paradox, quantum atmosphere and analog black holes.

Detection of quasimonochromatic, long-duration (continuous) gravitational wave radiation emitted by, e.g., asymmetric rotating neutron stars in our Galaxy requires a long observation time to distinguish it from the detector’s noise. If this signal is additionally microlensed by a lensing object located in the Galaxy, its magnitude would be temporarily magnified, which may lead to its discovery and allow probing of the physical nature of the lensing object and the source. We study the observational effect of microlensing of continuous gravitational wave signals for Galactic sources and lenses in the point mass lens approximation. In particular, we examine the regions of the parameter space that are promising for lensed CW searches and perform example simulations to demonstrate how the lensing effect affects the continuous wave signal. We show that an analytical lensing pattern can be identified from the lensed continuous wave signal using the time-domain $\mathcal{F}$-statistic search, as the estimated signal-to-noise ratio in each time-domain segment scales directly with the amplification factor.

We present a new pipeline designed for the robust inference of cosmological parameters using both second- and third-order shear statistics. We build a theoretical model for rapid evaluation of three-point correlations using our fastnc code and integrate it into the cosmosis framework. We measure the two-point functions ${\xi }_{\pm }$ and the full configuration-dependent three-point shear correlation functions across all auto- and cross-redshift bins. We compress the three-point functions into the mass aperture statistic $⟨{\mathcal{M}}_{\mathrm{ap}}^3⟩$ for a set of 796 simulated shear maps designed to model the Dark Energy Survey Year 3 data. We estimate from it the full covariance matrix and model the effects of intrinsic alignments, shear calibration biases and photometric redshift uncertainties. We apply scale cuts to minimize the contamination from the baryonic signal as modeled through hydrodynamical simulations. We find a significant improvement of 83% on the figure of merit in the ${\mathrm{\Omega }}_{\mathrm{m}}\text{−}{S}_8$ plane when we add the $⟨{\mathcal{M}}_{\mathrm{ap}}^3⟩$ data to ${\xi }_{\pm }$. We present our findings for all relevant cosmological and systematic uncertainty parameters and discuss the complementarity of third-order and second-order statistics.

Similarly to electromagnetic (EM) signals, gravitational lensing by intervening galaxies can also affect gravitational waves (GWs). In this paper, we estimate the strong-lensing rate of massive black hole mergers observed with LISA. Given the uncertainties in the source populations as well as in the population of galaxies at high redshift, we consider: six different source population models, including light and heavy seeds, as well as three lens population models, including redshift-independent and redshift-dependent evolution properties. Among all the scenarios explored, the expected number of strong lensed events detected in a 4-year observation time in LISA ranges between 0.13-231 with most of them having two (one) images detectable in the heavy (light) seed scenarios. The event numbers obtained correspond to 0.2%–0.9% of all detected unlensed events. Out of all the detectable strong-lensed events, up to 61% (in the light-seed scenario) and 1% (in the heavy-seed scenario) of them are above the detectability threshold solely due to strong lensing effects and would otherwise be undetectable. For detectable pairs of strong-lensed events by galaxy lenses, we also find between 72%–81% of them to have time delays from 1 week to 1 year.

We present a study of unbiased reconstruction of cosmic microwave background (CMB) polarization maps from data collected by modern ground-based observatories. Atmospheric emission is a major source of correlated noise in such experiments, complicating the recovery of faint cosmological signals. We consider estimators that require only minimal assumptions about the properties of the unpolarized atmospheric emission, instead exploiting hardware solutions commonly implemented in modern instruments, such as pairs of orthogonal antennas in each focal plane pixel, interleaving of the antenna orientation from pixel to pixel, and polarization signal modulation via a continuously rotating half-wave plate (HWP). We focus on two techniques: (i) statistical downweighting of low-frequency atmospheric signals and (ii) pair differencing (PD), which involves differencing the signals collected by two detectors in the same focal plane pixel. We compare their performance and contrast them with the idealized case where the atmospheric signal is perfectly known and can be cleanly subtracted. We show that PD can be derived from the maximum likelihood principle under very general assumptions about the atmospheric signal and is therefore optimal in terms of map sensitivity for essentially any such signal. Remarkably, in the absence of instrumental systematics, but with reasonable variations of detector noise properties, PD yields polarized sky maps with noise levels only slightly worse (typically a few percent) than the ideal reference case. While the downweighting method could in principle match or surpass this performance, it requires highly accurate models of the atmospheric signal, which are not readily available. The performance of PD will be affected by instrumental systematics and those leaking the atmospheric signal to the difference time stream may have particularly adverse impact. However, we expect that some of these effects, as shown in the case of gain mismatch, are efficiently mitigated by a continuously rotating HWP and, therefore, that in the context of modern CMB experimental setups PD could provide a competitive, numerically robust, and efficient practical solution for CMB polarization mapmaking without the need for atmospheric modeling.

The tomographic Alcock-Paczynski (AP) method, developed over the past decade, exploits redshift evolution for cosmological determination, aiming to mitigate contamination from redshift distortions and capture nonlinear scale information. Marked correlation functions (MCFs) extend information beyond the two-point correlation. For the first time, this study integrated the tomographic AP test with MCFs to constrain the flat $w$ cold dark matter ($w\mathrm{CDM}$) cosmology model. Our findings show that multiple density weights in MCFs outperform the traditional two-point correlation function, reducing the uncertainties of the matter density parameter ${\mathrm{\Omega }}_m$ and dark energy equation of state $w$ by 48% and 45%, respectively. Furthermore, we introduce a novel principal component analysis (PCA) compression scheme that efficiently projects high-dimensional statistical measurements into a compact set of eigenmodes while preserving most of the cosmological information. This approach retains significantly more information than traditional coarse binning methods, which simply average adjacent bins in a lossy manner, yielding an additional $\sim 40\%$ reduction in error margins. To assess robustness, we incorporate realistic redshift errors expected in future spectroscopic surveys. While these errors modestly degrade cosmological constraints, our combined framework, which utilizes MCFs and PCA compression within tomographic AP tests, is less affected and always yields tight cosmological constraints. This scheme remains highly promising for upcoming slitless spectroscopic surveys, such as the Chinese Space Station Telescope (CSST).

The values of the Hubble constant inferred from local measurements and the cosmic microwave background (CMB) exhibit an approximately $5\sigma$ tension. Some have suggested this tension is alleviated if matter is converted to dark radiation via dark matter decay. As it is not clear that dark matter decays, we instead examine the effects of converting matter to gravitational radiation via black hole mergers. We consider mergers of supermassive black holes (SMBHs), mergers of stellar-mass black holes, and the formation of SMBHs from mergers of smaller black holes. We find that these processes cannot alleviate the tension, as an unrealistically large merger rate, or an overproduction of SMBHs is required. We also consider whether one can use the integrated Sachs-Wolfe effect to constrain mechanisms that form SMBHs from mergers of smaller black holes. We find that this is also too small to be viable.

The structure of astrophysical objects is usually modeled under the assumption of hydrostatic equilibrium. However, actual configurations may deviate from perfect spherical or isotropic properties. Consequently, cosmic objects are expected to exhibit some degree of anisotropy. This consideration also extends to hypothetical dark structures, such as dark stars and dark matter halos. Although the nature of dark matter remains unknown, axionlike particles are strong candidates, suggesting that dark matter halos may have originated from bosonic configurations undergoing gravitational collapse, sustained by boson-boson interactions in the condensate state. This system is described by the Gross-Pitaevskii-Poisson equation. Furthermore, within the framework of the de Broglie–Bohm approach, quantum effects—encapsulated in the so-called quantum potential—may play a significant role in equilibrium astrophysical configurations. In this study, we examine a class of static anisotropic boson stars, which are nonminimally coupled to gravity. By including all these factors, we derive a generalized Lane-Emden-like equation and conduct a detailed analysis of the maximum degree of anisotropy that such systems can sustain, thereby identifying physically viable equilibrium configurations. Apart from focusing on the impact of anisotropic contributions, we find that for the so-called quantum polytropes (when the quantum potential is the main thing responsible for the equilibrium condition), the anisotropic factor and the gravitational field have opposite roles compared to the classical case. This leads to a new class of hydrostatic equilibrium objects.

Large-scale structure surveys can be used to measure the dipole in the cosmic microwave background (CMB), in the luminosity distances inferred from type-Ia supernova observations, and in the spatial distribution of galaxies and quasars. The measurements of these cosmic dipoles appear to be mutually inconsistent, even though they are expected to indicate the common observer velocity. This observational tension may represent a significant challenge to the standard model of cosmology. Here we study in detail what contributes to the cosmic dipoles from CMB, supernova, and galaxy survey in the standard $\mathrm{\Lambda }$ cold dark matter ($\mathrm{\Lambda }\mathrm{CDM}$) model, though our theoretical model can be applied beyond the standard model. While measurements of the cosmic dipoles yield the relative velocities between the source samples and the observer velocity, the motion of the observer is the dominant contribution in the conformal Newtonian gauge, and the intrinsic velocities of the samples fall steeply with increasing redshift of the sources. Hence the cosmic dipoles of CMB, type-Ia supernovae, and galaxies should be aligned but can have different amplitudes. We also clarify several misconceptions that are commonly found in the literature.

Gravitational lensing by a stellar microlens of mass $M$ forms two images separated by microarcseconds on the sky and has a time delay of $2\times {10}^{-5}(M/M_{\odot })$ seconds. Although we cannot resolve such microimages in the sky, they could be resolved in time if the source is a fast radio burst (FRB). In this work, we study the magnification ($|\mu |$) and time delay ($t_d$) distributions of microimages led by different microlens populations. We find that, in microlensing of typical strongly lensed (macro)images in galaxy lenses, microimages stemmed from a population of stellar mass microlenses in the $[0.08,1.5]M_{\odot }$ range and a second (dark) microlens population in $[{10}^{-3}–{10}^{-2}]M_{\odot }$ range reside in different parts of $|\mu |-t_d$ plane. For the global minimum macroimage, due to low stellar mass density, we find that the stellar population leads to peaks in autocorrelation at $>{10}^{-6}$ seconds, whereas the secondary population leads to peaks at $<{10}^{-6}$ seconds, allowing us to differentiate different microlens populations. However, an increase in stellar density introduces new peaks at $<{10}^{-6}$ seconds, which can pollute the inference about the presence of multiple microlens populations. In addition, we also show that the number of microimages, hence the number of peaks in the autocorrelation, is sensitive to the underlying stellar mass function, allowing us to constrain the stellar initial mass function (IMF) with FRB microlesning in the future. This work is a first step toward using FRB lensing to probe the microlens population within strong lenses, and more detailed studies are required to assess the effect of various uncertainties that we only discussed qualitatively.

Fermionic asymmetric dark matter (ADM) can be captured in neutron stars (NSs) via scatterings with the star constituents. The absence of dark matter annihilation due to its asymmetric nature leads to ADM accumulation in the NS core, potentially reaching densities sufficient to exceed the Chandrasekhar limit and trigger its gravitational collapse into a black hole (BH), eventually consuming the NS from within. Therefore, the existence and observation of old neutron stars provide a means to constrain the properties of ADM. We revisit previous constraints on the mass and scattering cross section off neutrons of fermionic ADM across a class of models. We critically examine common simplifying approximations used in the literature to derive these limits. Our analysis includes improved treatments of dark matter capture, thermalization, BH formation, accretion, and evaporation. We find that previous results can be relaxed by a few orders of magnitude once these effects are properly accounted for.

The Cherenkov Telescope Array Observatory (CTAO) will be a ground-based Cherenkov telescope performing wide-sky surveys, ideal for anisotropy studies such as cross-correlations with tracers of the cosmic large-scale structure. Cross-correlations can shed light on high-energy $\gamma$-ray sources and potentially reveal exotic signals from particle dark matter. In this work, we investigate CTAO sensitivity to cross-correlation signals between $\gamma$-ray emission and galaxy distributions. We find that by using dense, low-redshift catalogs like 2 MASS, and for integration times around 50 hours, this technique achieves sensitivities to both annihilating and decaying dark matter signals that are competitive with those from dwarf galaxy and cluster analyses.