arXiv subjects

Shao-Wen Wei

Publications and source records attributed to Shao-Wen Wei.

At least 37 records · Page 2Linked to original sources

arXiv2026

Topologically equivalent yet radiatively distinct orbits in EMRI system

Multiple potential wells for massive test particles, allowing distinct families of bound orbits to coexist, are a characteristic feature of certain exotic compact objects beyond general relativity. Taking the dyonic black hole as a representative example, we demonstrate that such multi-well geometries generically support multiple coexisting branches of bound orbits, in contrast to the single-branch behavior observed in the Schwarzschild spacetime. Crucially, the periodic orbits sharing identical rational rotation number, and hence identical topological indices can nevertheless produce \emph{radiatively distinct} gravitational waves in a representative extreme-mass-ratio inspirals: their amplitude modulation and harmonic content differ because each branch spans different regions of spacetime curvature. These ``topologically equivalent yet waveform-distinguishable'' signatures provide a direct observational probe of strong field gravitational dynamics beyond general relativity, potentially accessible to future space-based gravitational wave detectors.

gr-qc↗

arXiv2026

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.

gr-qc↗

arXiv2026

Magnetic field effects on spherical orbit in Kerr-Bertotti-Robinson spacetime: constraints from jet precession of M87*

The recently reported precession period of about $11.24$ years of the M87* jet provides a sensitive probe of strong field gravity and the electromagnetic environment in the immediate vicinity of supermassive black holes. In this work, we study the precession of the spherical orbit in the Kerr-Bertotti-Robinson geometry describing a rotating black hole immersed in a uniform electromagnetic field. Although the timelike geodesics is non-separable, we develop a Hamiltonian approach to investigate the spherical orbits. For sufficiently strong magnetic fields, the study shows that the spherical orbits can only exist within a finite radial range for given orbital inclination. Requiring the existence of the spherical orbits, we obtain an upper bound of the magnetic field, i.e., $B<0.33 M^{-1}$ for prograde and $B<0.0165 M^{-1}$ for retrograde motion. Furthermore, imposing the observed jet precession period, we obtain a significantly tighter constraint, $B\lesssim 0.0145 M^{-1}$, providing a new constrain on the magnetic field of M87* independent of the shadow. Our results provide unified constraints on the parameters of the KBR black hole and demonstrate that the jet precession offers a robust and complementary probe of magnetized black holes in the strong gravity regime.

gr-qc↗

arXiv2025

Deciphering black hole phase transitions through photon spheres

Black hole thermodynamics is a crucial and foundational aspect of black hole physics, yet its observational verification remains exceptionally challenging. The photon sphere of a black hole, a manifestation of strong gravitational effects, is intrinsically linked to its shadow, which has been directly captured through observations made by the Event Horizon Telescope. Investigating black hole thermodynamics from a gravitational perspective presents an intriguing avenue for research. This paper obtains an analytical formula for the coexistence curve and investigates the relationship between the thermodynamic phase transition and the photon sphere of a black hole with quantum anomaly. It proposes that the photon sphere encodes information about the black hole phase transition, arguing that the change in the photon sphere radius can serve as an order parameter characterizing the black hole's phase transition.

gr-qc↗

arXiv2025

Test fields and naked singularities: is the second law the cosmic censor?

It has been claimed that a Kerr-Newman black hole can generically be overspun by neutral test fields, and it has been argued that even when backreactions are taken into account, the black hole can still be destroyed. In this paper, we revisit the weak cosmic censorship conjecture for a Kerr-Newman black hole with a test scalar field and a neutrino field, and point out that the assumption in previous work regarding the energy and angular momentum of the test fields absorbed by the black hole violates the second law of black hole thermodynamics. By solving the test scalar field and neutrino field near the event horizon explicitly, we demonstrate that an extremal Kerr-Newman black hole cannot be overspun by a test scalar field but can be destroyed by a neutrino field. Our results indicate that the condition required to overspin an extremal Kerr-Newman black hole coincides with the condition needed to violate the second law of black hole thermodynamics. Furthermore, we observe that such a violation of the second law might inevitably result in a breakdown of the weak cosmic censorship conjecture.

gr-qc↗

arXiv2025

Exact black hole solutions in gravity with a background Kalb-Ramond field

In this work, we derive exact solutions for four-dimensional static spherically symmetric black holes and three-dimensional rotating black holes within a Lorentz-violating gravity theory. In this framework, Lorentz symmetry is spontaneously broken when a nonminimally coupled Kalb-Ramond tensor field acquires a nonzero vacuum expectation value. Building upon these solutions, we investigate the thermodynamic properties of the black holes using the Iyer-Wald formalism. Our findings reveal that the standard first law of thermodynamics and the Smarr relation remain valid for black holes in the presence of the Kalb-Ramond field.

gr-qc↗

arXiv2025

Equatorial periodic orbits and gravitational waveforms in a black hole free of Cauchy horizon

In this paper, we study the periodic orbits and gravitational wave radiation in an extreme mass ratio inspiral system, where a stellar-mass object orbits a supermassive black hole without Cauchy horizons. Firstly, by using the effective potential, the marginally bound orbits and the innermost stable circular orbits are investigated. It is found that the radius, orbital angular momentum, and energy increase with the hair parameter for both orbits. Based on these results, we examine one special type of orbit, the periodic orbit, around the black hole without the Cauchy horizon. The results show that, for a fixed rational number, the energy and angular momentum of the periodic orbit increase with the hair parameter. In particular, we observe a significant deviation from the Schwarzschild case for small hair parameter with a large amount of external mass outside the black hole horizon. Moreover, we examine the waveforms in the extreme mass ratio inspiral system to explore the orbital information of the periodic orbits and the constraints on the parameters of the black holes. The results reveal that the gravitational waveforms can fully capture the zoom-whirl behavior of periodic orbits. Moreover, the phase of the gravitational waves imposes constraints on the parameters of the black hole solutions. As the system evolves, the phase shift of the waveforms becomes increasingly significant, with cumulative deviations becoming more pronounced over time. Compared to the Schwarzschild black hole background, the waveform phase will advance for the central supermassive black hole without a Cauchy horizon.

gr-qc↗

arXiv2025

Effects of magnetic fields on spinning test particles orbiting Kerr-Bertotti-Robinson black holes

In this paper, we study the kinematic effects of spinning test particles orbiting the Kerr-Bertotti-Robinson black hole. Employing with the Mathisson-Papapetrou-Dixon equations, we explore the dynamics of precessing orbits and distinct orbital types, including circular orbits and innermost stable circular orbits. Our results reveal the substantial impact of the magnetic field on the trajectories of spinning particles, particularly in regions characterized by significant radial distances. More importantly, our study shows that an augmented magnetic field necessitates an increased orbital angular momentum to uphold spinning particles within their characteristic orbits at equivalent radial distances. Our result contributes valuable insights to the understanding of the spinning celestial object motion around black holes endowed with magnetic fields.

gr-qc↗

arXiv2025

Precession of spherical orbits for the spacetime without $\mathbb{Z}_2$ symmetry induced by NUT charge

Astrophysical evidence has hinted at the existence of a nonzero NUT charge, which breaks the $\mathbb{Z}_2$ symmetry of spacetime and induces novel features in geodesics. In this work, we investigate the Lense-Thirring precession of the spherical orbits in the Kerr-Taub-NUT spacetime, with particular emphasis on its connection to recent observations of black hole jet precession. We analyze the reflection symmetry breaking in trajectories of the spherical orbits and extract their precession angular velocity. It is worth noting that in the absence of spin, the spherical orbits reduce to tilted circular orbits without precession, whereas for nonzero spin, the precession angular velocity increases with the absolute value of the NUT charge. We then model the motion of particles near the warp radius of a tilted accretion disk using the spherical orbits and constrain the black hole parameter space based on the observed jet precession of M87*. The results indicate that regions with low spin and large NUT charge were excluded, and that the jet precession measurements cannot distinguish the sign of the NUT charge. The excluded region is larger for retrograde accretion disks than for prograde ones. We also find that this observation do not allow a clear distinction between black holes and naked singularities. Moreover, we also explore how black hole parameters influence the structure of accretion disk. These results have important theoretical and astronomical significance for us to deeply understand NUT space-time.

gr-qc↗

arXiv2025

Universal exponents of black hole phase transition at zero-temperature limit

In this work, we investigate the universal thermodynamic characteristics of black hole phase transitions at the zero-temperature limit. Our results reveal that, far below the critical point, the near zero-temperature region also exhibits universal properties. By employing the Maxwell equal area law and analyzing the coexistence curve of black hole phase transitions, we derive three universal exponents: $α=1$, $β=2$, and $γ=d-3$, where $d$ represents the spacetime dimension number. Furthermore, additional studies show that these exponents remain unchanged regardless of the black hole's charge and spin. These universal exponents provide valuable insights into enhancing our understanding of black hole thermodynamic phase transitions near zero temperature and shed light on the fundamental aspects of quantum gravity.

gr-qc↗

arXiv2025

Extended thermodynamical topology of black hole

Thermodynamical topology has emerged as a powerful framework for classifying the thermodynamical behavior of black holes. Three distinct yet complementary topological invariants have been employed to characterize black hole phases, spinodal curves, and critical points in black hole thermodynamics. In this work, we develop a unified framework that integrates these three topological approaches and introduce the concept of extended thermodynamical topology, providing a clear physical interpretation. As a first step, we apply this framework to black holes in Einstein gravity, systematically elucidating their phase structure in terms of topological invariants. We then extend our analysis to black holes in 7-dimensional Lovelock gravity, where novel thermodynamic phenomena naturally emerge from the topological perspective. Moreover, we explore the connection between critical exponents and the extended thermodynamical topology, uncovering a correspondence between the zeros of the $k$-th order vector field and the associated critical exponents. Our study demonstrates that extended thermodynamical topology offers a robust and fine-grained framework for analyzing and classifying black hole phase transitions.

hep-th↗

arXiv2025

Characteristic precessions of spherical orbit around a rotating braneworld black hole

We study the orbital dynamics and relativistic precession effects in the spacetime of rotating braneworld black holes within the Randall-Sundrum framework. For test particles on spherical orbits, we analyze three conserved quantities-energy, angular momentum, and Carter constant-and examine how the innermost stable spherical orbit depends on the tidal charge and orbital inclination. Compared to Kerr black holes, braneworld corrections significantly modify both nodal and periastron precession frequencies: positive tidal charges suppress precession rates, while negative charges enhance them. For stationary gyroscopes, we calculate the Lense-Thirring precession frequency and demonstrate its sensitivity to the tidal charge, black hole spin, and gyroscope orientation. Our results show that a positive tidal charge weakens frame-dragging effects even as it enhances gravitational attraction-offering a distinctive signature of extra-dimensional gravity. These results have important implications for astrophysical observations, including accretion disk behavior, stellar orbital dynamics, and gravitational wave detection. The modified orbital and gyroscopic precession provide new ways to test braneworld gravity in strong-field regimes.

gr-qc↗

arXiv2025

Evolution of innermost stable circular orbit and light ring of a charged black hole induced by the scalarization

In this paper, we investigate the dynamical evolution of the innermost stable circular orbit (ISCO) and light ring of a charged black hole during dynamical scalarization. This is achieved through nonlinear simulations within the framework of the Einstein-Maxwell-dilaton theory. Using the time-dependent metric derived from these simulations, we compute the radial effective potentials for timelike and null geodesics as functions of time. Our results demonstrate how the ISCO and light ring evolve as a hairless charged black hole transitions to a scalarized state. We find that dynamical scalarization induces an increase in the areal radii of both the ISCO and light ring. These findings provide new insights into black hole scalarization, particularly regarding the temporal evolution of the ISCO and light ring in a dynamically evolving spacetime.

gr-qc↗

arXiv2025

Fate of initially bound timelike geodesics in spherical boson stars

Boson stars are horizonless compact objects and they could possess novel geodesic orbits under the equilibrium assumption, which differ from those in black hole backgrounds. However, unstable boson stars may collapse into black holes or migrate to stable states, resulting in an inability to maintain the initially bound geodesic orbits within the backgrounds of unstable boson stars. To elucidate the fate of initially bound geodesic orbits in boson stars, we present a study of geodesics within the spherical space-times of stable, collapsing, and migrating boson stars. We focus on timelike geodesics that are initially circular or reciprocating. We verify that orbits initially bound within a stable boson star persist in their bound states. For a collapsing boson star, we show that orbits initially bound and reciprocating finally either become unbound or plunge into the newly formed black hole, depending on their initial maximal radii. {For initially circular geodesics, we have discovered the existence of a critical radius. Orbits with radii below this critical value are found to plunge into the newly formed black hole, whereas those with radii larger than the critical radius continue to orbit around the vicinity of the newly formed black hole, exhibiting nonzero eccentricities}. For the migrating case, a black hole does not form. In this case, the reciprocating orbits span a wider radial range. For initially circular geodesics, orbits with small radii become unbound, and orbits with large radii remain bound with nonvanishing eccentricities. This geodesic study provides a novel approach to investigating the gravitational collapse and migration of boson stars.

gr-qc↗

arXiv2025

Generalized Free Energy Landscapes from Iyer-Wald Formalism

The generalized free energy landscape plays a pivotal role in understanding black hole thermodynamics and phase transitions. In general relativity, one can directly derive the generalized free energy from the contributions of black holes exhibiting conical singularities. In this work, we extend this idea to general covariant theories. By employing Noether's second theorem, we present an alternative formulation of the Lagrangian, which can elucidate the role of conical singularities. We demonstrate that, in general, the contribution from conical singularities depends on the specific implementation of the regularization scheme and is not uniquely determined; this feature is explicitly exhibited and confirmed in three-dimensional new massive gravity. Nevertheless, these ambiguities can be absorbed into the second-order (and higher) corrections induced by conical singularities when the gravitational theory is described by the Lagrangian $L(g_{ab},R_{abcd})$. Moreover, for certain theories such as general relativity and Bumblebee gravity, this contribution simplifies to a well-defined result. However, the interpretation of the generalized free energy in Bumblebee gravity is somewhat different, with its extrema corresponding to the geometry of conical singularities. Our results uncover the particular properties of the generalized free energy beyond general relativity.

hep-th↗

arXiv2025

Holographic thermodynamics of a five-dimensional neutral Gauss-Bonnet AdS black hole

Motivated by the recent progress on the holographic dual of the extended thermodynamics for black holes in anti-de-Sitter (AdS) space, we investiggate the hologrphic thermodynamics for the five-dimensional neutral Gauss-Bonnet AdS black hole in the context of the anti-de Sitter/conformal field theory (AdS/CFT) correspondence. Through the extended bulk thermodynamics for the five-dimensional Gauss-Bonnet AdS black hole, we derive the first law of the CFT thermodynamics which is obtained by directly translating the arbitrary conformal factors in the dual CFT. In addition to the newly defined chemical potential $μ$ conjugating to the central charge $C$, we obtain other pairs of thermodynamics for the CFT, such as the temperature $\tilde{T}$ and the entropy $S$, the Gauss-Bonnet coupling constant $\tildeα$ and its conjugate variable $ \tilde{\mathcal{A}}$, the pressure $\mathcal{P}$ and its conjugate volume $\mathcal{V}$. In the fixed $C$, $\mathcal{V}$ and $\tildeα$ canonical ensemble, we obtain the canonical description of the CFT thermodynamics and observe the standard swallowtail behavior in the Helmholtz free energy vs the temperature plot. The self-intersection point of the Helmholtz free energy indicates the phase transition between the high and low entropy states of the CFT. By using Maxwell's equal area law, we get the critical point and coexistence curve for the high and low entropy phases of the CFT. Besides, we get the critical exponents for the CFT, and find that the critical point and critical exponents associated with the $\tilde{T}-S$ criticality of the CFT are the same as those of the five-dimensional Gauss-Bonnet AdS black hole.

hep-th↗

arXiv2025

Black hole thermodynamics from an ensemble-averaged theory

The path integral approach to a quantum theory of gravity is widely regarded as an indispensable strategy. However, determining what additional elements, beyond black hole or AdS spacetime, should be incorporated into the path integral remains crucial yet perplexing. We argue that the spacetime with a conical singularity in its Euclidean counterpart should be the most important ingredient to append to the path integral. Therefore, physical quantities should be ensemble-averaged over all geometries since they are described by the same Lorentzian metric. When the ensemble average is introduced, the Hawking-Page transition for the Schwarzschild-AdS black hole and the small-large black hole transition for the Reissner-Nordström-AdS black hole naturally arise as semi-classical approximations, when the size of the black hole system is much larger than the Planck length. Away from the semi-classical limit, the system is a superposition of different geometries, and the averaged quantities would deviate from the black hole thermodynamics. Expanding around the classical saddles, the subleading order of the Newton constant contributions can be derived, which are half of the Hawking temperature both for the Schwarzschild and Reissner-Nordström black holes. The result may imply a universal structure. The subsubleading terms and more intriguing physics that diverge from black hole thermodynamics are revealed. The ensemble-averaged theory provides a new way of studying subleading effects and extending the traditional AdS/CFT correspondence.

gr-qc↗

arXiv2025

Charged spherically symmetric and slowly rotating charged black hole solutions in bumblebee gravity

In this paper, we present charged spherically symmetric black hole solutions and slowly rotating charged solutions in bumblebee gravity with and without a cosmological constant. The static spherically symmetric solutions describe the Reissner-Nordström-like black hole and ReissnerNordström-(anti) de Sitter-like black hole, while the stationary and axially symmetric soltuions describe Kerr-Newman-like black hole and Kerr-Newman-(anti) de Sitter-like black hole. We utilize the Hamilton-Jacobi formalism to study the shadows of the black holes. Additionally, we investigate the effect of the electric charge and Lorentz-violating parameters on the radius of the shadow reference circle and the distortion parameter. We find that the radius of the reference circle decreases with the Lorentz-violating parameter and charge parameter, while the distortion parameter increases with the Lorentz-violating parameter and the charge parameter.

gr-qc↗