6,148 papers
The formation of a weak null singularity in the interior of generic rotating black holes
Given a characteristic initial value problem with smooth data representing a dynamical event horizon settling down to that of Kerr in the subextremal, strictly rotating range with suitable upper and lower bounds, we prove that a weak null singularity forms, across which the spacetime metric is continuously extendible but not Lipschitz extendible. The bulk of the proof is a stability argument showing that a dynamical Teukolsky field can be approximated by a linear Teukolsky field, whose linear instability was proved in previous works.
2604.04877Apr 2026
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Detecting gravitational waves by emission of photons from charged Weber bars
In this work, we propose a novel experimental set-up using charged resonant gravitational wave detectors. We exploit the semi-classical analogue of the Gertsenshtein effect where the gravitational wave acts as an modulator for the optomechanical system. We consider a cavity QED scenario where the Weber bar is placed inside an electromagnetically shielded cavity. We observer that when the gravitational wave falls on the Weber bar, it emits photon which signifies the detection of gravitational waves by the resonant bars. The frequency controlled spontaneous emission scenario will shed a new light on future generation of efficient gravitational wave detector models.
2604.04836Apr 2026
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2604.04784Canonical Uncertainty Relations for Madelung Variables in Curved Spacetime
We establish fundamental uncertainty relations for the hydrodynamic variables arising from the Madelung representation of quantum fields in curved spacetime. Through canonical quantization of the density $n$ and phase $θ$ variables and their conjugate momenta, we derive exact uncertainty principles that depend on spacetime geometry through the lapse function $N$ and spatial metric $γ_{ij}$. These relations reveal how gravitational fields modulate quantum fluctuations and provide first-principles constraints for scalar field dark matter models and stochastic quantum gravity.
2604.04784Apr 2026
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Gravitational waves production during preheating within GB gravity with monomial coupling
In this paper, we investigate the production of gravitational waves during the preheating era. To achieve this purpose, we consider Gauss-Bonnet inflation model with Power{\textendash}law potential, $V(φ)= V_0 φ^n$, and monomial Gauss-Bonnet coupling function, $ξ(φ)= ξ_0 φ^n$. We examine our model by comparing our findings with the current observational data. After that, we study the preheating stage by adopting an approach in which we establish a link between preheating duration, reheating phase and inflationary parameters. This step allows us to benefit from observational constraints imposed on inflation. Furthermore, we examine the production of gravitational waves during preheating epoch connecting the energy density to the preheating duration, $N_{pre}$, and then with the spectral index $n_s$. The generation of gravitational waves during preheating can satisfy observational constraints. In particular, the predicted present-day gravitational-wave energy density, expressed as a function of the scalar spectral index, is consistent with the Planck constraints for the choice of a dimensionless Gauss-Bonnet coupling parameter $α\equiv 4V_{0}ξ_{0}/3 = -1.5\times 10^{-6}$, an effective equation of state parameter $ω= 1/6$, and a preheating efficiency parameter $δ= 10^{5}$.
2604.04764Apr 2026
View2604.04731Subtleties in non-equilibrium horizon thermodynamics of modified gravity theories
Thermodynamic interpretations of gravity often arise from applying the Clausius relation to spacetime horizons. In modified gravity theories with higher-order equations of motion, such as f(R) and scalar-tensor gravity, this relation generally acquires additional entropy-production term. In this context, two distinct formulations have been proposed in literature: the non-equilibrium approach of Eling, Guedens, and Jacobson based on local Rindler horizons, and the thermodynamic formulation of cosmological apparent horizons in FLRW spacetimes. In this article, we present a detailed analysis of these approaches, and show that, even though both employ identical entropy balance relations that resemble non-equilibrium thermodynamics, the exact origin and role of each entropy-production term is fundamentally different. In the Rindler-horizon framework the extra term follows directly from consistency requirements related to the Bianchi identity, whereas in the apparent-horizon approach it is introduced solely to recover the Friedmann equations. Furthermore, we will see that the latter non-equilibrium contribution enters directly into dynamical equations of gravity, while the former does not. Finally, we also highlight the fact that thermodynamic descriptions of horizons in such modified gravity are not unique, and that equilibrium, and non-equilibrium descriptions can arise from different choices of thermodynamic variables. A clear understanding of these distinctions is therefore crucial for establishing a consistent and physically meaningful thermodynamic foundation for gravity beyond general relativity.
2604.04731Apr 2026
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Optical Appearance and Ringdown of Black Holes in a Kalb Ramond Field Coupled to Perfect Fluid Dark Matter
This paper investigates the optical and dynamical properties of a static spherically symmetric black hole in the presence of a Kalb--Ramond (KR) field coupled to perfect fluid dark matter (PFDM). We analyze the effects of the Lorentz-violating parameter $α$ and the dark matter parameter $λ$ on photon trajectories and their observational signatures in the strong-gravity regime. Furthermore, we study the quasinormal mode spectrum under scalar, electromagnetic, and gravitational perturbations, examining how the model parameters influence the characteristic oscillation frequencies and damping rates. In particular, the interplay between the effective potential structure and perturbative dynamics is clarified, and it is found that, within the validity of the eikonal approximation, the quasinormal modes of the black hole considered here exhibit good agreement with the properties of null geodesics. Our results show that the model parameters significantly affect both the optical appearance of the black hole and the dynamical features of the ringdown phase, providing potential observational constraints on Lorentz-violating effects and dark matter environments in strong-field regimes.
2604.04706Apr 2026
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EHT-Constrained Analysis of Shadow Deformation in Quantum-Improved Rotating Non-Singular Magnetic Monopole
We studied the shadow cast by a rotating Bardeen black hole within the framework of asymptotically safe gravity. The null geodesics were analyzed using the Hamilton Jacobi separation method to derive shadow observables. Our findings show that an increase in both the asymptotic safety parameter and the spin parameter leads to a decrease in the apparent shadow size and an increase in shadow distortion. The monopole charge of the black hole played an important role in the shadow profile. Furthermore, we compute the energy emission rate associated with varying values of the asymptotic safety parameter.
2604.04695Apr 2026
View2604.04639New Almost Universal Metrics
Plane waves and pp-waves are well-known universal metrics that solve all metric-based gravitational field equations. Similarly, the Kerr-Schild-Kundt class of metrics is almost universal: all metric-based gravitational field equations reduce to a linear scalar partial differential equation that always admits a solution. Here, we add a new member to this class of metrics and show that nonzero constant curvature pp-wave metrics are also almost universal. They reduce the generic gravity field equations to those of cosmological Einstein-Maxwell theory with null dust. The background of the pp-waves has the topology $\mathbb{R}^{1,1}\times S^{2}$ and provides the missing partner to the Nariai metric with ${\rm dS}^{2}\times S^{2}$ and the Bertotti-Robinson metric with ${\rm AdS}^{2}\times S^{2}$ topologies. These quantum-protected metrics are of clear interest. We exemplify our results by using the quadratic and cubic gravity theories.
2604.04639Apr 2026
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Preliminary study on the impact of stress-energy tensor compared to scalar field in Nonminimal Derivative model
In this article, we report the results of comparing the effect of using trace of stress-energy tensor versus real-valued scalar field in Nonminimal Derivative Coupling gravitation model, respectively denoted as NMDC-T and NMDC-phi. We employ the model into an incompressible star and see the effect of both models NMDC-T and NMDC-phi on the compactness and mass-radius relation. We find that coupling parameters of NMDC-T is less sensitive than NMDC-phi.
2604.04617Apr 2026
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Cosmic Inflation From Regular Black Holes
We study braneworld cosmology in quasi-topological gravity (QTG) with an infinite tower of higher-curvature terms, focusing on the case in which the bulk admits regular black hole solutions. We derive the $\mathbb{Z}_2$-symmetric junction conditions for a FLRW brane moving in a static, spherically symmetric bulk geometry, and obtain the corresponding modified Friedmann equations for the scale factor. We prove that, in the small scale factor regime, the brane generically approaches a de Sitter phase characterized solely by the length scale $\sqrtα$ of the higher-derivative terms, while the standard Einstein-gravity braneworld dynamics is recovered in the low-energy regime. We further provide a universal estimate for the number of e-folds of the de Sitter phase in terms of the ratio between the black hole scale and the scale of new physics $r_g/\sqrtα$. The inflationary regime is fully independent of the brane matter content and hence avoids the problem of trans-Planckian matter densities. Numerical integrations for explicit regular bulk solutions (Dymnikova-like and Hayward black holes) confirm these estimates and illustrate how the bulk black hole sector controls the onset and termination of inflation. This framework leverages the powerful properties of QTGs, defined only in $D\ge 5$, to study consequences for a four-dimensional universe.
2604.04601Apr 2026
View2604.04582Galileon versus Quintessence: A comparative phase space analysis and late-time cosmic relevance
We perform a comparative phase space analysis of the light mass Galileon model and standard Quintessence in the context of late--time cosmic acceleration. Focusing on a spatially flat FLRW background, we consider a cubic Galileon interaction supplemented by a scalar potential and examine three representative choices of the potential: a generalized cosh potential, a simple cosh potential, and a linear potential. By introducing suitable dimensionless variables, the cosmological field equations are reformulated as an autonomous dynamical system, allowing a systematic investigation of the stationary points and their stability properties. For the light mass Galileon scenario, we find that although the phase space admits scalar field dominated solutions, all critical points are of saddle type for the potentials considered. In particular, no stable late-time accelerating attractor emerges, even in the presence of de-Sitter like configurations. In contrast, the Quintessence limit admits stable de-Sitter attractors for cosh potentials, providing a viable description of the observed late--time acceleration. Our results highlight a key qualitative distinction between Galileon and Quintessence cosmologies and indicate that, within the light mass Galileon framework, the higher-order Galileon interactions may be required to realize a stable accelerating Universe.
2604.04582Apr 2026
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Stationary Einstein-vector-Gauss-Bonnet black holes
We study spontaneously vectorized black holes in Einstein-vector-Gauss-Bonnet theory with a quadratic coupling function. Besides the static, spherically symmetric black holes carrying an electric charge, there are uncharged static, axially symmetric black holes that possess a magnetic dipole moment. Both types possess radial excitations. The magnetic black holes are prolate. They are hotter than the Schwarzschild black holes and possess lower free energy. The domain of existence of the rotating vectorized black holes is bounded by the Kerr black holes, the spherically and axially symmetric static black holes, and the critical solutions.
2604.04568Apr 2026
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Gravity/thermodynamics correspondence via black hole shadows
The shadow of a black hole serves as a pristine window into the strong-gravity regime, with cuspy feature emerging as a smoking-gun signature of physics beyond the Kerr paradigm. In this paper, we extend the work of [arXiv:2601.15612 [gr-qc]] and study the detailed properties of the cuspy shadow by using the parametric expressions of the shadow boundary. From a topological perspective, we provide a rigorous topological classification of these shadows, categorizing them into distinct ``rectangular" and ``8-shape" topologies. Crucially, we establish a formal gravity/thermodynamics correspondence by mapping the cuspy shadow to the swallowtail behavior observed in thermodynamic free energy. We demonstrate that the self-intersection of the shadow boundary, marking a geometric phase transition, can be precisely determined through three independent but equivalently thermodynamic-like approaches. Furthermore, we analytically derive the critical exponents governing the emergence of these cusps, revealing that they are consistent with the mean-field universality class. Our results suggest that the observational features of black hole shadows are deeply rooted in the underlying gravitational thermodynamics, offering a novel framework to probe the fundamental nature of spacetime.
2604.04441Apr 2026
View2604.04259Matching Tidal Deformability (Wilson) Coefficients to Black Hole Love Numbers in Higher-Curvature Gravity
We present a consistent mapping between tidal deformability coefficients (tidal Love numbers) and Wilson coefficients in effective field theory (EFT) descriptions of higher-curvature theories of gravity. In this work, we focus on the connection between the static response of a non-spinning black hole and the corresponding Wilson coefficient governing tidal imprints in gravitational-wave signals. We analyze a set of control cases to identify the key ingredients required for a systematic computation and matching procedure. In doing so, we highlight shortcomings in existing results that rely on the standard matching approach used in General Relativity when applied to higher-curvature gravity theories. As an explicit demonstration, we compute the relevant coefficients for cubic gravity theories. Our findings bridge an important gap in the correspondence between tidal Love numbers and Wilson coefficients in EFT extensions of General Relativity, which had not been thoroughly explored previously.
2604.04259Apr 2026
View2604.04219A Conformal Boundary Ansatz for Warm Inflation Initialization: A Toy Model
We present a theoretical framework demonstrating a deterministic initialization mechanism for Warm Inflation via classical conformal boundary conditions. A persistent challenge in dissipative inflationary models is the "cold start" paradox: initializing the requisite thermal bath to generate the dissipative friction that subsequently sustains radiation production. Postulating an idealized, asymptotically scale invariant pre-inflationary phase, we mathematically prove that a conformal Weyl mapping to the emergent metric furnishes a finite, analytically derived initial radiation density. Implementing a spontaneous conformal symmetry-breaking ansatz, an emergent inflaton field is subjected to this inherited thermal bath. We analytically derive the initial kinematics of this framework, demonstrating that for strict sub-Planckian temperatures, the universe naturally initializes in the weak dissipative regime (Q << 1). The initial Hubble friction provided by the boundary radiation enables a smooth, deterministic kinematic handoff to the warm slow-roll steady-state attractor. As a mathematical proof-of-concept, this mechanism provides a fully realized framework to bypass the bootstrap problem of warm inflation.
2604.04219Apr 2026
View2604.04185Black Hole Persistence in New General Relativity
We investigate whether black holes can persist through the bounce with a minimal scale factor in a non-singular cosmology, whereby black holes from a previous contracting phase survive into the current expanding one. We do so by studying a generalized McVittie spacetime which embeds a spherically symmetric black hole in a positive spatial curvature bouncing FLRW cosmological background within the modified theory of teleparallel new general relativity. There are no further assumptions on the spacetime (e.g., on the form of the scale factor) initially, and the local evolution is derived from the field equations of the theory, utilizing a perturbative scheme which is valid ``near the bounce". To leading order we obtain a simple bounce solution similar to that in general relativity for a closed FLRW model with a positive cosmological constant, but in which the curvature term in the Friedmann equation is re-normalized within new general relativity. Qualitatively the minimum of the bounce at $t=0$ changes, but near the bounce the evolution remains symmetric. The central inhomogeneity evolves at higher perturbative orders, where the details depend on the arbitrary constants of the perturbative solution. Hence the evolution of the local horizon during the bounce changes qualitatively, where the effects depend on the signs of the perturbation, and the symmetry across the bounce is disrupted due to a linear term.
2604.04185Apr 2026
View2604.03996Raychaudhuri Equation and Weyl-Driven Shear: A Weak-Field Approach to Lensing and Gravitational Waves
The letter studies phenomena like gravitational wave propagation and gravitational lensing using the celebrated Raychaudhuri equation (RE) in the weak field limit. Newtonian analogue of Relativistic RE has been explored. In doing so, role of shear has been found to be extremely important in explaining these phenomena. Consequently, the RE for shear has been used in course of the study and importance of Weyl curvature tensor in lensing and gravity wave propagation has been explicitly shown using a damped harmonic oscillator approach.
2604.03996Apr 2026
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Testing the chaos bound in the spinor field of Einstein-Euler-Heisenberg-Anti-de Sitter spacetime
Violations of the chaos bound have been observed in scalar fields. In this work, we investigate the Lyapunov exponents of chaotic particles in the spinor field of an Einstein-Euler-Heisenberg-Anti-de Sitter spacetime, and test the validity of the chaos bound in this field. The influences of the black hole charge, the Euler-Heisenberg constant, cosmological constant, particle charge and total angular momentum on the exponents are analyzed. With other parameters fixed, chaos bound violations occur only within specific ranges of black hole charge, particle spin, or total angular momentum-unlike in Reissner-Nordström spacetimes, where violations intensify with larger parameter values. Notably, anti-alignment of particle spin with the $z$-axis can trigger violations even for small cosmological constants, while no violations arise for the spin aligned with the $z$-axis regardless of the cosmological constant. Our results show that the cosmological constant drastically reshapes chaos bound violation conditions compared to Reissner-Nordström spacetimes, highlighting the spin's pivotal role in chaos onset.
2604.03914Apr 2026
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Dymnikova-Schwinger quantum-corrected slowly rotating wormholes: Photon and spinning particle dynamics
This work studies light propagation near slowly rotating traversable wormholes supported by a quantum-inspired matter source. The model is based on the Dymnikova density profile, viewed as a gravitational analogue of the Schwinger mechanism, which yields a smooth, non-singular core. Quantum effects are included through the generalized uncertainty principle (GUP), introducing a minimal length scale while preserving regularity. Within a stationary and axisymmetric framework, we construct rotating wormhole solutions sustained by the GUP-corrected Dymnikova-Schwinger profile. The geometry satisfies key conditions such as asymptotic flatness and the flare-out requirement, and incorporates rotational features like frame dragging. We then examine photon motion via null geodesics. Both rotation and quantum corrections modify the photon sphere structure, with rotation producing a splitting between co-rotating and counter-rotating trajectories. This results in small asymmetries in photon paths and the shadow. These results provide a novel and consistent framework to probe quantum-gravity imprints in strong-field optics.
2604.03864Apr 2026
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Entanglement generation from gravitationally produced massless vector particles during inflation
We study the gravitational production of spectator massless vector particles in a single-field inflationary scenario, and the related entanglement generation across the Hubble horizon. Accordingly, we consider a quasi-de Sitter background evolution, with additional metric inhomogeneities induced by the inflaton quantum fluctuations. Afterwards, we compute the corresponding production amplitude and show that it depends only on the transverse polarizations, appearing \emph{de facto} gauge-invariant, consistently with our interpretation of the vector field as the electromagnetic one. We notice that particle wavelengths turn out to be small compared to the Hubble radius, thus favoring sub-Hubble production relative to super-Hubble one. In particular, highly energetic vector particles are preferentially produced and we show that polarization effects provide a significant contribution to this behavior. Moreover, the production of nearly collinear particle pairs appears as the most probable configuration, due to the background conformal invariance of the theory and the plane-wave (massless particle-like) nature of the metric perturbation. We thus specialize our treatment to super-Hubble scales, confirming their subdominant contribution to the number density of produced particles, albeit setting a corresponding lower bound on the reheating temperature. In this scheme, we explore superhorizon entanglement between sub- and super-Hubble field modes, computing the corresponding von Neumann entropy and discussing the effects of horizon crossing on the generation of primordial entanglement.
2604.03822Apr 2026
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