Gravitational-wave data from observed binary black hole coalescences have been demonstrated in recent analyses to validate the Hawking area theorem (HAT) for black hole horizons. The result of such analyses is imposed here as a criterion of absolute consistency on the logarithmic (in horizon area) corrections to the Bekenstein-Hawking area formula for the black hole entropy, when these corrections are computed both from nonperturbative quantum fluctuations of spacetime in matter-free quantum general relativity, as well as arising due to perturbative quantum matter field fluctuations around a stationary classical black hole background spacetime. This criterion of absolute consistency is seen to be obeyed provided certain restrictions ensue on the spin-parity and number of species of the spectrum of quantum matter fluctuations. Such constraints appear to restrict the beyond-Standard-Model (BSM) part of the matter fluctuation spectrum. Some species of the constrained, yet-unobserved BSM particle spectrum are currently under active consideration in particle cosmology as candidates for dark matter.

We revisit the Ricci-flat metrics in four dimensions that are stationary and algebraically special, together with the locally asymptotically flat conditions in the generalized Bondi-Sachs framework. We show that the Einstein equation is reduced to the Laplacian equation on the celestial sphere. The solutions consist of two pairs of arbitrary holomorphic and antiholomorphic functions analogous to the Virasoro modes. We prove that the higher modes of one pair of the (anti)holomorphic function contain an infinite tower of soft hairs from the perspectives of the asymptotic supertranslation charges. We verify that different modes of the soft hairs are distinct solutions that cannot be connected by diffeomorphism, using the Weyl invariants associated to the solutions. Extending the construction to Einstein-Maxwell theory introduces a third pair of (anti)holomorphic functions, arising from the Maxwell tensor, which generates soft electric hair. We further present an exact soft-hairy solution of Einstein-Maxwell theory with a cosmological constant, offering a potential understanding of soft hair from the AdS/CFT correspondence.

We investigate the deflection of photons in the strong deflection limit within static and axisymmetric spacetimes possessing reflection symmetry. As the impact parameter approaches its critical value, the deflection angle exhibits a logarithmic divergence. This divergence is characterized by a logarithmic coefficient and a constant offset, which we express in terms of the coordinate-invariant curvature quantities evaluated at the unstable circular photon orbit. The curvature contribution is encoded in the electric part of the Weyl tensor, reflecting tidal effects, and the matter contribution is encoded in the Einstein tensor, capturing the influence of local energy and pressure. We also express these coefficients using the Newman-Penrose scalars. By exploiting the relationship between the strong deflection limit and the quasinormal modes, we derive a new expression for the quasinormal mode frequency in the eikonal limit in terms of the curvature scalars. Our results provide a unified and coordinate-invariant framework that connects observable lensing features and quasinormal modes to the local geometry and matter distribution near compact objects.

We investigate the structure of nontrivial maximally symmetric vacua and compact-object solutions in shift-symmetric scalar-tensor theories. Focusing on Horndeski gravity, we derive consistency conditions directly from the field equations to identify the subclasses that admit Minkowski and de Sitter vacua with a nontrivial scalar field. In doing so, we obtain a filtering mechanism that operates independently of observational data. In this context, we introduce the notion of stealth vacua, where the scalar field remains active without altering the vacuum. Following this, we examine the theoretical framework of Horndeski theories that admit homogeneous geometries and we extract the implicit form of the solution pertaining to the entire family of theories. Building upon these frameworks, we construct exact solutions in beyond-Horndeski gravity by applying a linear disformal transformation to the regularized Einstein-Gauss-Bonnet black hole. This procedure yields solitonic spacetimes with scalar hair as well as black holes carrying primary scalar hair, demonstrating how disformal maps can qualitatively modify solution properties. We delineate the parameter space in which the transformation is well defined and analyze the solutions. Our results provide both a principled criterion for selecting viable Horndeski models and a framework for exploring rich solution spaces in beyond-Horndeski gravity.

We develop a causal hydrodynamic model that provides an effective macroscopic description of the field-theoretic dynamics during the early stages of reheating. The inflaton condensate is treated as a homogeneous background coupled to a relativistic fluid that represents its inhomogeneous fluctuations. Within the divergence-type theory framework derived from kinetic considerations, the model captures essential dissipative and nonequilibrium effects while remaining stable and causal. We find that the coupling between the oscillating condensate and the fluid induces a parametric resonance in the tensor sector, leading to the amplification of the viscous stress tensor and the generation of gravitational waves with a characteristic spectral peak. The predicted spectrum agrees with lattice simulations performed with CosmoLattice. This hydrodynamic approach offers an effective bridge between microscopic field dynamics and macroscopic cosmological observables.

In this paper, we investigate the production of Majorana fermionic dark matter (DM) via the Higgs portal, considering both freeze-in and freeze-out mechanisms during and after the postinflationary reheating phase. We assume that the Universe is reheated through the decay of the inflaton ($\varphi$) into a pair of fermions $f$ and $\overline{f}$ via the interaction $y\varphi \overline{f}f$, where $y$ is the dimensionless Yukawa coupling. Our analysis focuses on how the nonstandard evolution of the Hubble expansion rate and the thermal bath temperature during reheating influence DM production. Additionally, we examine the impact of electroweak symmetry breaking (EWSB), distinguishing between scenarios where DM freeze-in or freeze-out occurs before or after EWSB. We further explore the viable DM parameter space and its compatibility with current and future detection experiments, including XENONnT, LUX-ZEPLIN, XLZD, and collider searches. Moreover, we incorporate constraints from the Lyman-$\alpha$ bound to ensure consistency with small-scale structure formation.

The Bernardeau-Nishimichi-Taruya (BNT) transform provides a powerful framework for analyzing tomographic cosmic shear data by improving the localization of shear correlations in physical scale. It operates by performing a linear combination of the shear data vector in $\ell$-space, yielding a transformed vector that is better localized in both redshift and $k$-space. BNT is particularly useful for estimating cosmological parameters while minimizing the impact of poorly understood nonlinear physics, without discarding large amounts of information as is typically done with simple scale cuts. In our previous work, we showed that BNT outperforms traditional weak-lensing analyses; however, that study did not include intrinsic alignments (IA). In the present work, we assess the robustness of our BNT-based $k$-cut framework in the presence of realistic IA models. We consider two cases: (i) when the assumed IA model used in sampling is close to, but not identical to, the true one, and (ii) when the assumed IA model is significantly biased compared to the true one. In the first case, the $k$-cut framework yields precise and unbiased $S_8$ constraints even with limited knowledge of large-scale modes. Using Euclid-like mock data and a stringent $k$-cut of $k\le 0.1{\mathrm{Mpc}}^{-1}$ for all tomographic bins, we found that BNT can constrain $S_8$ with a precision better than 2% while non-BNT has lost all constraining power. In the second case, the BNT transform serves as a powerful diagnostic tool, revealing internal inconsistencies in $k$-space and redshift-space both exceeding $5\sigma$ when the functional form of the sampling and fiducial IA models differ fundamentally.

We present a new method for measuring the $E_G$ statistic that combines two CMB secondaries—the kinematic Sunyaev-Zel’dovich (kSZ) effect and CMB lensing—for the first time to probe gravity on linear scales. The $E_G$ statistic is a discriminating tool for modified gravity theories, which leave imprints in lensing observables and peculiar velocities. Existing $E_G$ measurements rely on redshift space distortions (RSD) to infer the velocity field. Here, we employ kSZ velocity reconstruction instead of RSD, a complementary technique that constrains the largest-scale modes better than the galaxy survey it uses. We construct a novel ${\widehat{V}}_G$ estimator that involves a ratio between cross-correlations of a galaxy sample with a CMB convergence map and that with a 3D kSZ-reconstructed velocity field. We forecast for current and upcoming CMB maps from the Atacama Cosmology Telescope and the Simons Observatory (SO), respectively, in combination with three spectroscopic galaxy samples from the Dark Energy Spectroscopic Instrument (DESI). We find cumulative detection significances in the range $S/N\sim 20–55$, which can robustly test the scale-independent $E_G$ prediction under general relativity (GR) at different effective redshifts of the galaxy samples ($z\approx 0.73$, 1.33, 1.84). In particular, the $\mathrm{SO}\times \mathrm{DESI}$ luminous red galaxies measurement would be able to distinguish between GR and certain modified gravity models, including Hu-Sawicki $f(R)$ and Chameleon theories, with high confidence. The proposed ${\widehat{V}}_G$ estimator opens up a new avenue for stress-testing gravity and the $\mathrm{\Lambda }\mathrm{CDM}+\mathrm{GR}$ model at the largest observable scales.

After the inflationary phase, the Universe enters the preheating phase, during which the inflaton field rolls down its potential and oscillates. When the potential significantly deviates from a parabolic shape at its minimum, these oscillations trigger an instability in the scalar perturbations, leading to their amplification. This phenomenon, known as self-resonance, has important implications in cosmology. Notably, since scalar perturbations couple to tensor perturbations at second order in the equations of motion, this amplification results in the production of gravitational waves, referred to as scalar-induced gravitational waves (SIGWs). In this study, we investigate the production of SIGWs during the preheating phase for a class of inflationary models known as $\alpha$-attractors, characterized by a single parameter $\alpha$. We focus on small values of this parameter, specifically $\alpha \sim \mathcal{O}({10}^{-1}–{10}^{-4})$, where the self-resonance effect is particularly pronounced. We obtain lower bounds on this parameter, ${\log }_{10}(\alpha )>-3.71(-3.51)$ for the T-model and ${\log }_{10}(\alpha )>-3.48(-3.19)$ for the E-model, assuming a duration of preheating of 1 e-folds (5 e-folds). These bounds are obtained based on the energy density of SIGWs constrained by big bang nucleosynthesis, which ultimately translates into lower bounds on the tensor-to-scalar ratio, $r>6.54\times {10}^{-7}(1.03\times {10}^{-6})$ for the T-model and $r>1.11\times {10}^{-6}(2.14\times {10}^{-6})$ for the E-model. Note that these bounds on $\alpha$ and $r$ are derived within the linear framework of tensor fluctuations at the level of equations of motion, which nevertheless include scalar-scalar-tensor interactions with metric and matter fields. However, fully nonlinear approaches, with all higher-order metric fluctuations, would be needed in the future to further validate these conclusions.

Assembly bias, which is the variation in halo clustering at fixed mass driven by formation history, has long been predicted by numerical simulations but remains difficult to confirm observationally. Previous studies have reported evidence for halo assembly bias by dividing samples according to galaxy stellar mass using various methods. In this work, we present observational measurements of halo assembly bias based on the luminosity of spectroscopically confirmed brightest cluster galaxies (BCGs). Using cluster catalogs and shear measurements from the Dark Energy Spectroscopic Instrument Legacy Imaging Surveys, we employ a mass-dependent halo-bias model to disentangle halo bias from its underlying mass dependence in galaxy-galaxy lensing and clustering measurements. We confirm that brighter BCGs are less strongly clustered on large scales, with a relative bias ratio deviating from unity at the $\sim 3\sigma$ level, suggesting the presence of assembly bias. Similar qualitative trends are also found in the FLAMINGO and MillenniumTNG hydrodynamical simulations, strengthening the connection between galaxy luminosity and halo formation history.

Semiclassical Hawking evaporation is expected to break down at some point in a black hole’s evolution as the effects of quantum gravity become important. In particular, it has been argued that the so-called memory-burden effect could cause black holes to become stabilized by the information that they carry, thereby suppressing the rate at which they undergo Hawking evaporation. It has furthermore been suggested that this opens a new mass window, between ${10}^4\mathrm{g}\lesssim M\lesssim 10^{10}\mathrm{g}$, over which primordial black holes could constitute the dark matter of our Universe. We show for the first time that this is true only if the transition from the semiclassical phase of a black hole to its memory-burdened phase is practically instantaneous. If this transition is instead more continuous, Hawking evaporation will persist at relevant levels throughout the eras of big bang nucleosynthesis and recombination, leading to stringent constraints which rule out the possibility that black holes lighter than $\sim 4\times {10}^{16}\mathrm{g}$ could make up all or most of the dark matter. More broadly, our analysis demonstrates that even if departures from the semiclassical Hawking evaporation occur as proposed, they must be both drastic and abrupt to open viable new mass windows for primordial black hole dark matter.

Cosmic voids are magnetized at the level of at least ${10}^{-17}\mathrm{G}$ on Mpc scales, as implied by blazar observations. We show that an electrically conducting plasma is present in the voids, and that, because of the plasma, diffusion into the voids of galactic fields generated by a mean-field dynamo is far too slow to explain the present-day void magnetization. Indeed, we show that even in the presence of turbulence in the voids, dynamo-generated galactic fields diffuse out to a galactocentric radius of only 200–400 kpc. Therefore, it is challenging to meet the required volume filling-factor of the void magnetic field. We conclude that a primordial origin remains the most natural explanation to the space-filling weak fields in voids.

Extreme mass ratio inspirals (EMRIs) are key sources for the future space-based gravitational wave detector Laser Interferometer Space Antenna (LISA) and are considered promising probes of fundamental physics. Here, we present the first complete Bayesian analysis of EMRI signals in theories with an additional massless scalar, which could arise in an extension of general relativity or of the Standard Model of particle physics. We develop a waveform model accurate at adiabatic order for equatorial eccentric orbits around spinning black holes. Using full Bayesian inference, we forecast LISA’s ability to probe the presence of new fundamental fields with EMRI observations.

It is well known that, at zero wave number, the nonhydrodynamic frequencies of uncharged kinetic theory are purely imaginary. On the other hand, it was recently shown that, in resistive magnetohydrodynamics, the interplay between the Israel-Stewart relaxation equation and the Ampère-Maxwell law can give rise to a pair of oscillating nonhydrodynamic modes. In this work, we analyze this phenomenon in detail. We first demonstrate that these oscillatory modes are exact solutions of the Drude model, corresponding to ordinary plasma oscillations. We then invoke the Onsager-Casimir principle to explain that their oscillatory nature reflects the distinct $PT$-transformation properties of the degrees of freedom: the distribution function is even, while the electric field is odd. Finally, we establish that, in a kinetic theory of charged particles, there can be at most one such pair of oscillatory modes per spatial dimension, while all other modes still must sit on the imaginary axis.

We have surveyed all conventional methods proposed or conceivable for obtaining resolved images of an Earth-like exoplanet. Generating a $10\times 10\mathrm{pixel}$ map of a $1R_{\oplus }$ world at 10 pc demands $\approx 0.85\mu \mathrm{as}$ angular resolution and photon collection sufficient for $\mathrm{SNR}\gtrsim 5\mathrm{per}$ “micropixel.” We derived diffraction-limit and photon-budget requirements for (i) large single-aperture space telescopes with internal coronagraphs, (ii) external starshades, (iii) space-based interferometry (nulling and non-nulling), (iv) ground-based extremely large telescopes with extreme adaptive optics, (5) pupil-densified “hypertelescopes,” (vi) indirect reconstructions (rotational light-curve inversion, eclipse mapping, intensity interferometry), and (vii) diffraction-occultation by Solar System bodies. Even though these approaches serve their primary goals—exoplanet discovery and initial coarse characterization—each remains orders of magnitude away from delivering a spatially resolved image. In every case, technology readiness falls short, and fundamental barriers leave them 2–5 orders of magnitude below the angular resolution and photon-budget thresholds needed to map an Earth analog even on decadal timescales. Ultimately, an in situ platform delivered to $\lesssim 0.1\mathrm{AU}$ of the target could, in principle, overcome both diffraction and photon-starvation limits—but such a mission far exceeds current propulsion, autonomy, and communications capabilities. By contrast, the solar gravitational lens—providing on-axis gain of $\sim {10}^{10}$ and inherent $\mu \mathrm{as}\text{−}\mathrm{scale}$ focusing once an imaging spacecraft reaches heliocentric distances beyond $\gtrsim 550\mathrm{AU}$—appears uniquely capable of simultaneously meeting both the resolution and photon-budget requirements. If the several mission-specific risks (coronal calibration, focal-plane scanning, deconvolution) can be retired, the solar gravitational lens could enable true, resolved surface images and spatially resolved spectroscopy of Earth-like exoplanets in our stellar neighborhood.

Axionlike particles (ALPs) can be produced in the hot dense plasma of fireballs that develop in the initial stage of $\gamma$-ray burst (GRB) outflows. They can transport an enormous amount of energy away from the jet by propagating out of the fireball. The photons produced by the eventual decay of such ALPs do not reach a sufficient density to rethermalize through pair production, preventing fireball Re-emergence. Thus, the production of heavy ALPs disrupts the fireball and dims GRBs, allowing bright GRB observations to strongly constrain the existence of heavy ALPs. By adding ALP interactions to existing models of GRB fireballs, we set competitive bounds on the ALP-photon coupling down to $g_{a\gamma \gamma }\sim 4\times {10}^{-12}{\mathrm{GeV}}^{-1}$ for ALPs in the mass range of 200 MeV–5 GeV.

In this work, I discuss neutron stars with hyperons and antikaon condensate. To fix their coupling constants with the vector mesons of the quantum hadrodynamics, I use a unified scheme imposing that the Yukawa coupling is an invariant under SU(3) and SU(6) groups. Combining with the G-parity, I show that some expected results of the kaon and antikaon interaction with the nucleus are reobtained. In the same sense, the naive quark-isospin counting rule is restored in the SU(6) limit. Furthermore, the G-parity combined with the SU(3) gives us a clear picture of the role played by each meson in the kaon condensation. Numerical results show that the presence of antikaons severely compromises the stiffening of the equation of state by breaking the SU(6) symmetry.

The Moon has been regarded as a natural Weber bar capable of amplifying gravitational waves (GWs) for detecting events across a wide range of frequencies. However, accurately determining the amplification effects remains challenging due to the absence of 3D numerical simulation methods. In this study, we develop a high-order 3D finite element method (spectral-element method, SEM) to numerically simulate the lunar response to GWs below 20 mHz. We verify the accuracy of our method by comparing the resonant peaks of our results with those from semianalytical solutions and find that the frequency deviation is less than 3% for the first peak at about 1 mHz and less than 0.8% for the subsequent peaks up to 10 mHz. Using this method, we evaluate the amplification of GW signals due to 3D topographic effects of the Moon, and we find enhancements at a series of specific frequency components. These results highlight the non-negligible effect of surface topography on the lunar response to GWs, as a fundamental factor that holds significant implications across both global and regional analyses. Our work paves the way for a comprehensive evaluation of the Moon’s resonant response to GWs, helpful for the strategic planning of lunar GW detections.

We explore the equation of state (EOS) for neutron star matter combined with dark matter and investigate the influence of dark matter on neutron star properties. We also analyze the impact of symmetry energy on dark matter admixed neutron stars, incorporating the effects of the ${\mathrm{\Lambda }}_v$ coupling. Using the relativistic mean field model with the S271 parameter and ${\mathrm{\Lambda }}_v$ values of 0.000 and 0.030, we investigate the interaction between fermionic dark matter and pure nucleonic matter through the Higgs portal mechanism. Our results indicate that the presence of dark matter softens the EOS and reduces the tidal deformability of neutron stars. The GW170817 event imposes restrictions on the tidal deformability of binary neutron stars, ruling out stiff equations of state. We observe that the Fermi momentum ($k_F^{\mathrm{DM}}$) of dark matter has a more significant impact on neutron star properties, such as maximum mass, radius, and tidal deformability, compared to the ${\mathrm{\Lambda }}_v$ coupling. Nevertheless, our results for S271 with ${\mathrm{\Lambda }}_v=0.000$ and 0.030, incorporating fermionic dark matter, are consistent with the tidal deformability limit derived from the GW170817 observation.

We consider the theory of a higher-derivative (HD) real scalar field $\varphi$ coupled to a complex scalar $\sigma$, the coupling of the $\varphi$ and $\sigma$ being given by two types, ${\lambda }_{\sigma \varphi }{\sigma }^{†}\sigma {\varphi }^2$ and ${\xi }_{\sigma \varphi }{\sigma }^{†}\sigma {({\partial }_{\mu }\varphi )}^2$. We evaluate $\varphi$ one-loop corrections $\delta V(\sigma )$ to the effective potential of $\sigma$, both the contribution from the positive norm part of $\varphi$ and that from the negative norm part (ghost). We show that $\delta V({\sigma }_{\mathrm{cl}})$ at ${\sigma }_{\mathrm{cl}}\to \infty$, where ${\sigma }_{\mathrm{cl}}$ is a classical value of $\sigma$, is positive, implying the stability of $\delta V({\sigma }_{\mathrm{cl}})$ by the HD one-loop radiative corrections at high energy.