arXiv subjects

Takamasa Kanai

Publications and source records attributed to Takamasa Kanai.

16 recordsLinked to original sources

arXiv2026

Black Hole Entropy and Holographic Entanglement Entropy in DGP Brane Gravity

We investigate the relation between gravitational entropy and holographic entanglement entropy in braneworld gravity with gravitational dynamics localized on the brane. We first consider the DGP brane model, in which an Einstein-Hilbert term is included in the brane action, and derive the condition under which the gravitational entropy of a braneworld black hole agrees with the holographic entanglement entropy. We show that the two entropies coincide when a specific condition involving the extrinsic curvature of the brane is satisfied. In particular, this condition is automatically satisfied for static configurations. We then generalize the brane-localized Einstein-Hilbert term to higher-curvature gravitational theories. For Lovelock gravity and $f(R)$ gravity on the brane, we derive the corresponding conditions for the equality between gravitational entropy and holographic entanglement entropy and show that they take the same form as that obtained for Einstein gravity. Although the equality is not guaranteed for general stationary configurations, the required condition is satisfied for static braneworld black holes, leading to an agreement between the two entropies. These results clarify the relation between gravitational entropy and holographic entanglement entropy in braneworld gravity and contribute to a deeper understanding of holography in braneworld settings.

hep-th↗

arXiv2026

On the (In)equivalence of de Sitter and Holographic Entanglement Entropies in Lovelock Gravity

We investigate the relation between de Sitter entropy and holographic entanglement entropy in higher-curvature gravity and its braneworld realization. Using the canonical formulation of the gravitational action and the Euclidean gravitational path integral, we derive the de Sitter entropy, including contributions from higher-curvature surface terms, and compare it with the holographic entanglement entropy obtained from the corresponding entropy functional. We first consider Gauss-Bonnet gravity and show that the two entropies coincide for static asymptotically de Sitter braneworld spacetimes on the RS II model, while they generally differ for stationary spacetimes. The mismatch in the stationary case arises from an extrinsic-curvature contribution associated with the constant-time surface, which vanishes for static configurations but is generally nonzero for stationary geometries. We then extend the analysis to general Lovelock gravity and show that the agreement between the de Sitter entropy and holographic entanglement entropy persists for static asymptotically de Sitter braneworld spacetimes in the RS II model beyond the Gauss-Bonnet case. We also comment that the same distinction between static and stationary configurations applies to braneworld black holes: the black hole entropy agrees with the holographic entanglement entropy in the static case, while the two generally differ for stationary braneworld black holes. Our results clarify the relation between gravitational and holographic entropies in higher-curvature gravity and provide a broader perspective on holographic correspondence in Lovelock theories and their braneworld realizations.

hep-th↗

arXiv2026

Polarization-Dependent Photon Propagation, Quasinormal Modes, and Gravitational Lensing in Higher-Curvature Effective Theories

We investigate the impact of higher-curvature corrections on photon propagation within an effective field theory framework and their observational consequences in strong gravitational fields. We consider polarization-dependent modifications to photon trajectories in static and spherically symmetric spacetimes, focusing on Schwarzschild and Reissner--Nordström black hole backgrounds. Using the geometrical optics approximation, we derive the effective metrics governing photon propagation and study the resulting polarization-dependent shifts of the photon sphere. We compute the corresponding quasinormal modes in the eikonal limit and analyze their polarization dependence. We further investigate gravitational lensing, focusing on polarization-dependent corrections to the deflection angle in both weak- and strong-field regimes. In the strong-deflection regime, we find that even perturbatively small EFT corrections modify the coefficient of the logarithmically divergent part of the deflection angle, resulting in a potentially observable difference from the uncorrected case. This suggests that strong gravitational lensing may provide a sensitive probe of small higher-curvature corrections. While extracting EFT information directly from QNM frequencies is more subtle, QNMs may provide complementary information to gravitational lensing in future studies. Our results establish a framework for probing higher-curvature effects through polarization-dependent strong-field observables.

gr-qc↗

arXiv2026

Distinguishing Dymnikova and Schwarzschild Black Holes through Gravitational Lensing with EFT-Corrected Photon Propagation

We investigate whether a Dymnikova regular black hole can be observationally distinguished from a Schwarzschild black hole through strong gravitational lensing, taking into account effective field theory (EFT) corrections to photon propagation. We derive the modified photon propagation law induced by non-minimal couplings between the electromagnetic field and spacetime curvature and analyze the resulting photon trajectories in the Dymnikova spacetime. Within the strong deflection limit, we derive the EFT corrections to the photon sphere and the strong-deflection coefficients characterizing the logarithmically divergent behavior of the deflection angle. Although the EFT corrections are parametrically small, their effects can become relevant in the strong-deflection regime, where the deflection angle is highly sensitive to photon propagation near the critical orbit. We evaluate the strong-deflection observables for representative values of the Dymnikova parameter $\ell$ and compare them with the corresponding Schwarzschild results. We find that EFT corrections to photon propagation leave characteristic imprints on the strong-lensing observables. Furthermore, the contribution of the EFT corrections becomes more pronounced as the Dymnikova parameter $\ell$ approaches its critical value, indicating that the near-critical regime provides a particularly sensitive setting in which curvature-dependent corrections to photon propagation may affect gravitational lensing. These results suggest that strong gravitational lensing, together with EFT-induced modifications of photon propagation, may provide a means of distinguishing Dymnikova regular black holes from Schwarzschild black holes.

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arXiv2026

Gravitational Lensing of Hayward Black Holes with EFT-Corrected Photon Propagation

We investigate whether a Hayward regular black hole can be observationally distinguished from a Schwarzschild black hole through strong gravitational lensing when effective field theory (EFT) corrections to photon propagation are taken into account. We derive the modified photon propagation law induced by non-minimal couplings between the electromagnetic field and spacetime curvature, and analyze the resulting photon trajectories in the Hayward spacetime. Using the strong deflection limit, we derive the corrections to the photon sphere and the logarithmically divergent part of the deflection angle. Although the EFT corrections are parametrically small, their effects can be enhanced near the critical propagation region, where the deflection angle exhibits a logarithmic divergence. We evaluate the strong-deflection observables for representative values of the Hayward parameter and compare them with the Schwarzschild case. We find that EFT corrections to photon propagation can leave characteristic imprints on strong-lensing observables. Furthermore, the contribution of the EFT corrections becomes more pronounced as the Hayward parameter $g^3$ approaches its critical value, indicating that curvature-dependent corrections to photon propagation can become particularly relevant in the near-critical regime. These results suggest that strong gravitational lensing may provide a means of distinguishing Hayward regular black holes from Schwarzschild black holes.

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arXiv2026

Probing Effective Field Theory Corrections with Quasinormal Modes and Gravitational Lensing in Reissner-Nordström Black Holes

Effective field theory (EFT) provides a systematic framework for parametrizing possible higher-energy corrections to general relativity through higher-curvature interactions. In this work, we investigate gravitational lensing in both weak- and strong-field regimes for EFT-corrected Reissner-Nordström black hole spacetimes, focusing on both weakly charged and near-extremal configurations. Using the strong deflection limit formalism, we derive the corresponding corrections to the deflection angle, photon sphere radius, critical impact parameter, and strong lensing coefficients induced by higher-derivative curvature-electromagnetic interactions. Our analysis is restricted to purely geometrical corrections associated with modifications of the background spacetime geometry, without including polarization-dependent corrections to the photon propagation law. We show that strong gravitational lensing observables in charged black hole backgrounds can provide complementary probes of effective interactions between gravity and electromagnetic fields. These results suggest that future high-precision observations of strong lensing phenomena may place constraints on higher-curvature EFT couplings beyond general relativity.

gr-qc↗

arXiv2026

EFT Corrections to Photon Propagation and Gravitational Lensing in an Ellis-Bronnikov Wormhole

We investigate strong gravitational lensing by an Ellis-Bronnikov (EB) wormhole in the presence of effective field theory (EFT) corrections to photon propagation. We derive the modified photon propagation law induced by non-minimal couplings between the electromagnetic field and spacetime curvature, which leads to polarization-dependent photon trajectories in the EB wormhole spacetime. Using the strong deflection limit, we derive the corrections to the photon sphere and the logarithmically divergent part of the deflection angle. Although the EFT corrections are parametrically small, their contributions can become appreciable near the photon sphere. In particular, the $R_{μν}F^{μρ}F^ν{}_ρ$ interaction, which is nonvanishing for the EB wormhole but absent in the Schwarzschild spacetime, contributes to the strong-deflection coefficients. This may provide a distinctive lensing signature for observationally distinguishing wormholes from black holes.

gr-qc↗

arXiv2026

Photon Surfaces in Higher-Curvature Gravity: Implications for Quasinormal Modes and Gravitational Lensing

Effective field theory (EFT) provides a systematic framework to describe possible deviations from general relativity through higher-curvature corrections to the gravitational action, capturing low-energy effects of an underlying fundamental theory. In this work, we investigate quasinormal modes (QNMs) and both weak and strong gravitational lensing in static, spherically symmetric spacetimes, focusing on the behavior of null geodesics near the photon sphere. Adopting the strong deflection limit formalism developed by Bozza, we derive the logarithmic divergence structure of the deflection angle and explicitly separate the divergent and regular contributions. Within a simplified setup with $2M=1$, we analyze how deviations from general relativity, parametrized in an EFT framework, modify key observables such as the photon sphere radius, the critical impact parameter, and the coefficients governing the strong deflection expansion. We show that these quantities encode direct information about higher-curvature corrections to the gravitational action. Our results demonstrate that strong-field observables provide a sensitive probe of EFT corrections, and that precision measurements of gravitational lensing and QNM spectra could place constraints on EFT couplings beyond general relativity, offering a novel observational window into quantum gravity-inspired effects.

gr-qc↗

arXiv2026

Analytical Study of Deflection Angle and Time Delay in Kerr Spacetime with Modified Propagation

We investigate gravitational lensing in Kerr spacetime in the presence of a modified photon propagation law arising from higher-curvature effective field theory corrections. Adopting a deformed dispersion relation, we analytically derive the deflection angle and the propagation time delay for null trajectories in a rotating background. We show that the modified propagation leads to explicit and calculable deviations from the standard Kerr predictions, affecting both the bending angle and the time delay. These corrections exhibit a nontrivial dependence on the black hole spin and are expected to become more relevant in the strong-field regime. In particular, near the photon region-where the spin-dependent geometry influences photon trajectories-such effects may play a role in shaping observable propagation features. Our results establish a concrete and systematic framework to quantify deviations from standard photon propagation in gravitational lensing. They further indicate that observables such as relativistic image separations and time delays provide a potential avenue to probe ultraviolet corrections to gravity in strong-field environments.

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arXiv2026

Ultraviolet Behavior of the Wheeler-DeWitt Equation in Horava-Lifshitz Gravity

We investigate the quantum structure of black hole interiors in Horava-Lifshitz gravity by analyzing the Wheeler-DeWitt equation in minisuperspace. Focusing on the ultraviolet regime, where higher-order spatial curvature terms dominate, we derive analytical solutions in this UV limit for both the original Horava-Lifshitz action and its analytically continued counterpart. We study their behavior near the event horizon and the classical singularity, with particular attention to the interpretation of the wave function in terms of the annihilation-to-nothing scenario proposed in general relativity. In this paper, we have considered cases in which the two-dimensional spatial section is spherical, planar, or hyperbolic, as well as models with positive, negative, or vanishing cosmological constant. In all cases, we find that the terms dominating in the ultraviolet regime, together with the effects of the running scaling parameter, act to suppress the annihilation-to-nothing behavior. These results suggest that, at least within the range explored in this study, the characteristic annihilation-to-nothing behavior does not appear in the ultraviolet regime of Horava-Lifshitz gravity, and provide a new perspective on the understanding of singularity resolution in quantum gravity.

gr-qc↗

arXiv2026

Quantum Dynamics of the Schwarzschild Interior in Ashtekar-Barbero Variables with Minimal Length Effects

We study the quantum dynamics of the Schwarzschild interior in the Ashtekar-Barbero formulation, focusing on the fate of the classical singularity and the annihilation-to-nothing scenario. Using minisuperspace Wheeler-DeWitt quantization, we first analyze the standard Schrödinger representation and show that the annihilation-to-nothing behavior appears only for a specific choice of factor ordering and is not generic. We then introduce a generalized uncertainty principle (GUP), which induces minimal-length effects through a deformation of the canonical algebra. Solving the modified Wheeler-DeWitt equation and constructing Gaussian wave packets localized at the horizon, we find that the annihilation-to-nothing behavior is suppressed once the GUP corrections are included. Our results indicate that minimal-length effects qualitatively alter the quantum interior dynamics and challenge the robustness of this scenario as a mechanism for singularity resolution.

gr-qc↗

arXiv2026

Higher curvature corrections to the black hole Wheeler-DeWitt equation and the annihilation to nothing scenario

We revisit Yeom's annihilation-to-nothing scenario using a modified Wheeler-DeWitt (WDW) equation incorporating higher-curvature corrections. We show that, once these corrections are taken into account, the WDW wave function exhibits severe divergences arising from contributions near the classical singularity. These divergences indicate that the low-energy effective field theory (EFT) description breaks down in this regime. Given that general relativity (GR) itself is merely a low-energy effective field theory (EFT) of an underlying ultraviolet (UV) theory, our results suggest that any attempted resolution of the black hole singularity cannot be reliably discussed within the EFT framework. Our analysis does not contradict Yeom's conjecture, but emphasizes that the annihilation-to-nothing scenario should be discussed within a UV-complete theoretical framework. It further clarifies that any genuine resolution of the singularity necessarily requires a framework capable of appropriately describing ultraviolet physics, such as degrees of freedom beyond those captured by GR or dynamics consistently defined up to arbitrarily high energy scales.

gr-qc↗

arXiv2026

Wheeler-DeWitt Equation for Black Hole Interiors in Asymptotically Safe Gravity

In this work, we analyze the Wheeler-DeWitt equation with scale-dependent gravitational couplings within the framework of asymptotically safe gravity. In the Hamiltonian formulation based on a renormalization-group improved Einstein-Hilbert action, the consistency of the theory and the Poisson algebra of constraints have been clarified. Within this framework, we show that, despite the explicit scale dependence of Newton's constant, the classical solutions are generically unaffected by the running of the coupling. We then derive the Wheeler-DeWitt equation incorporating the scale dependence of the gravitational couplings and analyze its solutions in the minisuperspace framework. In the classical limit, while the scale dependence of Newton's constant does not affect the classical behavior, the running of the cosmological constant can contribute to the classical solutions. Moreover, we show that the quantum behavior in the ultraviolet regime acts toward suppressing singularity formation in all cases, independently of how the renormalization-group scale is identified with spacetime coordinates and of the relative magnitudes of the ultraviolet fixed points of the running Newton's constant and cosmological constant.

gr-qc↗

arXiv2025

Wormholes as perturbations of near-horizon black hole geometries: no-go theorems within effective field theories

We reformulate the construction of wormhole solutions as perturbations around near-horizon geometries of near-extremal Reissner-Nordström black holes in four dimensions and equal-angular-momenta Myers-Perry black holes in five dimensions. When the negative Casimir energy is taken as the source, this framework reduces to the Maldacena-Milekhin-Popov construction for magnetically charged wormholes. We then show that, in contrast, such perturbative constructions cannot be realized within the effective field theory approach to higher-derivative corrections. Remarkably, this conclusion holds irrespective of the specific form of the correction terms. The key observation is that the enhanced symmetries in the near-horizon region severely constrain the effective energy-momentum tensor near the throat. This prevents the formation of the traversable throat structure. Our analysis therefore establishes no-go theorems: traversable wormholes cannot arise perturbatively from Reissner-Nordström or Myers-Perry black holes in an effective field theory approach. Their realization would require either new ingredients, such as Casimir energy, or black holes with reduced symmetry.

gr-qc↗

arXiv2024

Cutoff Scale of Quadratic Gravity from Quantum Focusing Conjecture

We derive the cutoff length scale of the quadratic gravity in $d \geq 5$ dimensional spacetime by demanding that the quantum focusing conjecture for the smeared quantum expansion holds at the classical level. The cutoff scale has different dependence on the spacetime dimension depending on the sign of the coupling constant of the quadratic gravity. We also investigate a concrete example of the 5-dimensional Schwarzschild spacetime and directly confirm that the quantum focusing conjecture holds when the quantum expansion is smeared over the scale larger than our cutoff scale.

hep-th↗

arXiv2023

Entropy Bound and a Geometrically Nonsingular Universe

Bousso's entropy bound is a conjecture that the entropy through a null hypersurface emanating from a two-dimensional surface with a nonpositive expansion is bounded by the area of that two-dimensional surface. We investigate the validity of Bousso's entropy bound in the spatially flat, homogeneous, and isotropic universe with an adiabatic entropy current. We find that the bound is satisfied in the entire spacetime in which a cutoff time is introduced based on the entropy density and the energy density. Compared to the previously used prescription which puts a cutoff near the curvature singularity, our criterion for introducing the cutoff is applicable even to a nonsingular universe. Our analysis provides an interpretation of the incompleteness implied by the recently proposed singularity theorem based on the entropy bounds.

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