ALT In this paper, we examine the new black holes of Einsteinian cubic gravity within the framework of Born-Infeld-type electrodynamics. Initially, we establish the differential equations of motion that characterize an innovative collection of charged black hole solutions in Einsteinian cubic theory. Next, we compute the thermodynamic quantities of these black holes for the case of vanishing bare cosmological constant. We consider this situation because the model is unitary only for the asymptotically flat solutions that allow horizons with spherical topology. We also present that the first law of thermodynamics is fulfilled for these objects. Finally, we examine how the nonlinearity of electric field, electric charge and cubic coupling parameter can impact the local thermal stability of our simulated black holes in both canonical and grand canonical ensembles.

ALT Kehle and Unger have recently shown that self-gravitating charged classical scalar fields can collapse to form extremal Reissner-Nordström (eRN) black holes in finite time, thus violating the third law of thermodynamics (TLT). Reall has subsequently proved that the formation of an eRN black hole in gravitational collapse is impossible if the mass-to-charge ratio of the field exceeds unity, m/e≥1. In the present compact paper we conjecture, using quantum considerations, that the Reall bound is not sharp. In particular, we point out that the electric field of a charged system with charge Q will spontaneously polarize the vacuum in the regime (eQ/ℏ)²>(mQ/ℏ)²+1/4, thereby creating pairs of charged particles that discharge the black hole and ensure the quantum validity of the TLT in this regime. Motivated by the TLT, we conjecture that the classical Reall bound can be strengthened such that classical considerations would prevent eRN black holes from forming dynamically in the regime m/e≥√(1

ALT Excitations of the neutron star (NS) fundamental mode (f-mode) during a binary NS inspiral or from a glitching pulsar can produce gravitational waves (GWs) that will be detectable with the next generation of detectors, opening the door to GW asteroseismology of neutron stars. There exist approximately equation-of-state (EOS)-insensitive, or "universal," relations that relate the f-mode to other NS properties. These universal relations have typically been identified with relatively small, selective EOS samples. To more thoroughly explore the parameter space, we examine the f-modes for a large sample of piecewise-parametric EOSs by solving the linearized fluid perturbation equations for the f-mode frequency and damping time in full general relativity. We utilize our sample to evaluate the EOS-sensitivity of previously-proposed universal relations (URs) for both the f-mode frequency and damping time. We find that URs that depend on combinations of only NS mass and radius have significant

ALT The time-domain gravitational waveform emitted during the scattering of two nonspinning compact bodies is computed in the extreme-mass-ratio limit. It provides a time-domain description of the gravitational radiation emitted during the encounter and complements previous first-order self-force calculations, which have primarily been formulated in the frequency domain. In this way, the present results provide a complementary representation of the radiative dynamics and facilitate a direct comparison between time-domain and frequency-domain approaches to the gravitational-wave signal. The waveform is accurate to the fifth post-Minkowskian (three-loop) level and seventh post-Newtonian order, and will serve as a benchmark for future calculations by other methods, to first order in the mass ratio. The results have been already tested in a previous work by constructing the energy and angular momentum fluxes, thereby computing the corresponding radiative losses at the 5PM and 4PM level, respec

ALT Élie Cartan established that the metric and intrinsic curvature of a D dimensional embedded manifold M could be determined by tracing the response of another surface N of the same dimensionality, as it is rolled without slipping and twisting on M. In the context of spacetime geometry, this construction underpins the MacDowell-Mansouri formulation of General Relativity. We consider extensions of this framework that correspond to rolling of a shape with twisting and with shape evolution; it is shown that these naturally describe torsion and non-metricity respectively. Cartan-geometric formulations of teleparallel gravity and symmetric teleparallelism are discussed in addition to further manifestations of non-metricity in first-order formulations of gravity.

ALT We extend a previous study of the radial stability of solitonic boson stars by nonlinearly evolving them under aspherical perturbations, and by studying their formation from the collapse of scalar clouds. We focus in particular on models previously identified as radially stable, despite having positive binding energy, which ordinarily suggests that dispersion of all scalar matter is energetically preferred. A mode analysis of our 3+1 evolutions produces no evidence for the presence of a non-radial instability in any radially stable model, including those with positive binding energy. However, we do find evidence that such models do not generically form via gravitational cooling. We also find that it is possible to form another kind of compact object, which undergoes long-lasting radial oscillations and hence cannot be described as a stationary boson star. These objects may be characterized, we suggest, by energetically favoured multi-oscillating solutions to the Einstein-Klein-Gordon e

ALT We analyze the radiative properties of a general class of static and spherically symmetric black holes described by three independent shape functions, that encompass a broad family of regular and quantum-corrected geometries. We consider a minimally coupled massless scalar field, and derive the Hawking temperature and graybody factor for the different geometries. While the Hawking temperature is determined by the near-horizon geometry, the graybody factor depends on the scattering properties of the entire exterior spacetime, and therefore exhibits a richer dependence on the deformation parameters, frequency, and angular mode. Then we particularize to geometries that describe slight deformations of the Schwarzschild black hole, and obtain analytic expressions for the leading corrections to the graybody factor. Finally, we apply our results to several specific well-known black-hole models, including Reissner-Nordström, Bardeen, Hayward, Simpson-Visser, as well as geometries inspired by l

ALT We study the spinoptics equations for test electromagnetic wave in the Reissner-Nordström spacetime. The explicit and hidden symmetries of this background allow the complex null tetrad parallel-propagated along the null geodesic to be constructed explicitly. From this tetrad we obtain the evolution equations for the deviation of the ray from the null geodesic and for the tilting angle of its orbital plane. In these equations the charge term enters with a sign opposite to the mass term. Numerical integration confirms that the gravitational spin Hall effect becomes weaker with increasing charge: at a fixed impact parameter away from the critical value, the magnitude of the dimensionless tilting angle decreases with Q. As the turning point approaches the photon sphere, its magnitude grows firstly, and then exhibits an oscillatory behavior. Since the physical tilting angle is proportional to the reduced wavelength, it remains small whenever the spinoptics approximation is applicable. A div

ALT We derive analytic response functions for Unruh–DeWitt detectors coupled to real, massless, conformally coupled scalar fields, to distinguish the effects of the field spectrum and global geometry from those of the interaction protocol. For Gaussian-switched static pairs in Minkowski, anti-de Sitter, and de Sitter spacetimes, we obtain the leading-order excitation probabilities and two-detector coherences in spacetime dimension D=d+1≥3. Time-ordered coherence requires distinct spatial worldlines; the local response and single-excitation coherence also admit coincidence. For equal-redshift pairs, Gaussian switching separates the gap dependence of the time-ordered coherence. In de Sitter space, KMS detailed balance fixes the gap that maximizes the ratio of nonlocal coherence to local excitation, giving a single-gap test for the existence of leading-order entanglement and restricting any entangling gaps to one bounded interval. When entanglement is present, the concurrence itself peaks at

ALT We study the Petrov classification and Weyl double copy of the four-dimensional bulk metric dual to a 2+1-dimensional relativistic Rindler fluid at first order in the relativistic gradient expansion. Upon imposing the fluid equations, the leading Weyl curvature is determined by the fluid vorticity and shear. At this order, the bulk geometry is generically of Petrov type II, with a type D branch for shear-free flows with nonzero vorticity and a type N branch for irrotational flows with nonzero shear. For the type D branch, we construct a purely magnetic Maxwell single copy on a fixed Rindler background and distinguish exact source-free solutions with a constant magnetic field from local perturbative solutions valid through first order in gradients. For the type N branch, we obtain a family of algebraic Weyl double copies parametrized by β. We derive explicit field strengths and gauge potentials for β=0 and β=1, together with the local Cauchy-Riemann conditions imposed by Maxwell's equat

ALT We apply the Poincaré-Lindstedt method to the perturbed Binet equation describing conservative dynamics of the perturbed Kepler problem. We show that a simple treatment of divergent terms directly determines the frequency shift of the radial motion and hence the periastron advance. We provide explicit expressions for polynomial, logarithmic and inverse power perturbations, extend the procedure to higher perturbative orders and to problems involving several perturbation parameters. Applying this method to different physical effects relevant to compact binaries, we recover known results. We also obtain new contributions to the periastron advance, including the leading-order effects of arbitrary mass- and current-type tidal multipoles and mass-type spin-induced multipoles, the NNLO current-type tidal quadrupole contribution, electromagnetic electric-dipole contributions to NNLO and the eccentric corrections to the electric charge. Finally, we illustrate how the method can be directly appl

ALT Classical soft theorems govern the non-analytic structure of electromagnetic and gravitational radiation in the low-frequency regime, with the gravitational memory effect providing the canonical realization of the classical soft graviton theorem. While the soft behavior of radiation from hyperbolic scattering is well understood, its realization in gravitationally bound systems remains less explored. In this work, we study the soft structure of gravitational waveforms generated by compact binaries, focusing on the scattering of emitted radiation off the static background curvature within the multipolar post-Newtonian framework. We isolate the infrared (IR) logarithms associated with hereditary effects, including the tail-of-memory, and their higher generalizations with n-tail insertions. The resulting amplitudes exhibit a Laurent expansion in frequency space consistent with the Sahoo-Sen logarithmic soft theorems, thereby establishing a direct correspondence between gravitational memory

ALT Extreme-mass-ratio inspirals (EMRIs), systems in which a stellar-mass compact object spirals into a supermassive black hole (M₁), are prime targets for the space-based gravitational-wave interferometers and are acutely sensitive to their astrophysical environment. We quantify the joint imprint of a dark matter (DM) spike and an accretion disk on the waveforms of eccentric, equatorial Kerr EMRIs, integrating four modular effects—DM dynamical friction, DM self-gravity, Newtonian accretion-disk torques, and disk self-gravity—into a fifth post-Newtonian (5PN) augmented analytic kludge (AAK) waveform model, and assess their measurability via a Fisher-matrix analysis. The DM dynamical-friction dephasing peaks at M₁∼ 10⁶ M⊙, reaching ∼ 10²–10³ rad; there the DM spike slope is measurable to sub-percent precision and both DM channels are unambiguously detectable, while omitting DM biases the intrinsic parameters significantly. At M₁≳ 10⁸ M⊙ the DM and disk self-gravity channels dominate their d

ALT A first-order phase transition (PT) alters a compact star on two scales: globally, via growth of a quark-matter core, and microscopically, via collision of quark bubbles, driving a simultaneous gravitational-wave (GW) emission in the kHz and MHz bands. Using a constrained ensemble of model-agnostic equations of state, we follow the accretion-driven evolution of proto-neutron stars through the PT and compute the resulting multi-band GW signal. The correlations found between the kHz emission and the MHz burst could help constrain nuclear matter and the physics of the PT. A delayed neutrino burst should accompany the signal, with the delay set by the details of the PT, thus providing a prime multi-messenger source.

ALT We present a new Plebanski formulation of General Relativity. The key difference is that we work with a gauge vector field derived from the Lanczos potential of the Weyl tensor. We show that, on shell, the gauge vector field encodes all nontrivial gravitational degrees of freedom and, in a suitable Lorentz gauge, Bianchi identities ensure that this gauge vector field satisfies a source-free wave equation for Ricci-flat spacetimes. This description suggests new ways of interpreting the true geometrical degrees of freedom with applications in both classical and quantum gravity.

ALT This investigation aims to test the validity of general relativity (GR) on kiloparsec scales via galaxy-scale strong gravitational lensing (SGL) combined with multiple cosmological probes. To circumvent the circularity problem induced by the presumption of a cosmological model based on GR, we apply the distance sum rule in the Friedmann-Lemaitre-Robertson-Walker (FLRW) metric to constrain the post-Newtonian parameter gamma PPN and spatial curvature Omega k independently of any cosmological model. The study introduces two methodological improvements: (i) parameterizing the dark-energy evolution factor with second-order Chebyshev orthogonal polynomials, which ensures uniformly high convergence across the full redshift baseline while retaining Omega k as an explicit free parameter; (ii) extending the original two-probe configuration (SGL + Type Ia supernovae) to a four-probe joint analysis that includes baryon acoustic oscillations and cosmic chronometers. Our results show that gamma PPN

ALT There are strong motivations to modify gravity in the ultraviolet as well as the infrared. Such modifications are usually pursued independently from one another. Using the predictive power of asymptotically safe quantum gravity, we can constrain the effective-field-theory coefficients of scalar-tensor theories and thereby connect ultraviolet and infrared modifications of gravity. We focus on two non-minimal couplings, which are naturally generated in asymptotic safety and belong to the Horndeski Lagrangian only if the couplings satisfy a specific ratio. A priori, one would expect to find a negative answer to the question in our title. Surprisingly, we find that despite the constraints from asymptotic safety, this ratio can be achieved for a specific value of the cosmological constant. We interpret this as a non-trivial hint that asymptotically safe scalar-tensor theories could be free of extra propagating degrees of freedom in the infrared. We further find that the same result holds in

ALT We investigate the cosmological implications of a power-law f(Q, B) gravity model, where Q denotes the non-metricity scalar and B is the associated boundary term. We employ the Noether symmetry approach to identify the admissible functional form of the gravitational Lagrangian and to obtain the corresponding conserved quantities and exact cosmological solutions. Using the exact solution, we find that for this model parameter condition α+β>³⁄₂, the model exhibits the accelerating phase of the Universe. Furthermore, we have also discussed the model with recent observational data using a Bayesian Markov Chain Monte Carlo analysis. We consider different combinations of Cosmic Chronometers (CC), Pantheon+ & SH0ES, and DESI DR2 observations to constrain the model parameters and the Hubble constant H₀. The inferred value of H₀ depends on the adopted dataset combination, ranging from a higher value for the CC+Pantheon+ combination to a lower value for CC+DESI DR2, with the latter yielding H₀=6

ALT We study large-overtone quasi-normal modes of a massive scalar field in a four-dimensional Schwarzschild de-Sitter black hole in the presence of a wall placed at the static sphere. Dirichlet boundary condition is imposed at the wall. At leading order the quasi-normal modes with large overtones scale as n for n≫ 1 and are inversely proportional to the bouncing time. We analyze correction terms up to n⁻¹ order in the asymptotic expansion.

ALT Modeling the full inspiral-merger-ringdown signal requires combining analytically controlled inspiral physics with the nonlinear strong-field information supplied by numerical relativity. We represent the numerical relativity contribution beyond an analytic inspiral waveform as residual amplitude and phase corrections. Retaining the leading-order frequency-domain amplitude and the 3.5 Post-Newtonian TaylorF2 phase, we use a Kolmogorov-Arnold network to learn these residual corrections from SXS waveforms. After training, the learned corrections are stored as explicit spline functions, so waveform evaluation no longer requires the network itself. On 75 simulations excluded from training and model selection, the model achieves a median flat-noise mismatch of 2.7×10⁻⁵. Our results demonstrate a machine learning driven waveform modeling strategy in which numerical relativity augments, rather than replaces, analytically known waveform structure.