arXiv subjects

Shao-Wen Wei

Publications and source records attributed to Shao-Wen Wei.

At least 19 recordsLinked to original sources

arXiv2026

An asymptotically conical regular black hole in four-dimensional nonpolynomial quasitopological gravity

In this work, we construct an asymptotically conical regular black hole in four-dimensional nonpolynomial quasitopological gravity. Starting from a linear choice of the reduced function, which yields an asymptotically conical Schwarzschild-like solution, we introduce a nonlinear deformation that preserves the leading asymptotic cone while producing an exact black hole solution with a de Sitter core and finite curvature invariants. We further establish the corresponding black hole thermodynamics for both solutions within the Hamiltonian and Wald frameworks. The entropy contains rational and logarithmic terms in the regular model, and both solutions satisfy the first law of black hole thermodynamics.

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arXiv2026

Black hole free energy landscapes from constrained instantons

We apply gravitational path integral factorization to provide a semiclassical interpretation of generalized black hole free energy landscapes at fixed external temperature and angular velocities. Boundary integral transforms express the formal partition function as an integral over constrained sectors labeled by complete local partial-Neumann data on an auxiliary hypersurface. Independent variation establishes paired regular subregion solutions as constrained instantons, with Lagrange multipliers supporting lapse and tangential shift jumps that accommodate thermal and rotational mismatches. For selected nonextremal stationary families with an asymptotic boundary, the constrained saddle action takes the form $I_{\rm constr}=β\mathcal F_{\rm gen}=β(E_{\mathcal B}-Ω_{\mathcal B}^{I}J_{\mathcal B,I})-S$, with $β=T^{-1}$. Here $E_{\mathcal B}$ and $J_{\mathcal B,I}$ are renormalized Hamiltonian charges and $S$ is the black hole entropy, whose contribution to the action comes from the regular horizon cap. Interior stationary points of the landscape correspond to smooth equilibrium saddles when the retained variations independently span the entropy and angular momentum directions. We extend the construction to local, parity-even $f(\mathrm{Riemann})$ theories without curvature derivatives by retaining the complete auxiliary interface data. The same thermodynamic form follows with Wald entropy, without a small-deficit expansion. Schwarzschild and Kerr black holes illustrate the Einstein construction, while five-dimensional static AdS black holes in Einstein--Gauss--Bonnet gravity and the rotating BTZ branch of new massive gravity provide explicit checks of the higher-curvature extension.

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arXiv2026

Thermodynamics of rotating black holes with constrained primary hair

An exact rotating geometry need not define a black hole in equilibrium when its surface gravity varies across the horizon. We construct an asymptotically flat, non-Kerr subfamily of the aligned null solutions of generalized Proca theory whose outer horizon is exactly Killing and isothermal to second order in rotation. The horizon conditions constrain the vector hair, and integrability of the normalized horizon charge fixes the remaining second-order amplitude. Computing the complete gravitational and nonminimal vector surface charges, we obtain the asymptotically normalized mass and total angular momentum, and derive a logarithmic Hamiltonian entropy. The first law holds in both independent directions of the resulting two-parameter solution space. We express the mass as a function of entropy and angular momentum, recover the geometric thermodynamic potentials, and establish a scale-corrected Smarr relation that retains the dimensionful coupling. The exact metric defines the geometry, while equilibrium thermodynamics is consistently restricted to second order in spin.

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arXiv2026

Linear stability matrix and Lyapunov exponents for stationary spacetime

Lyapunov exponents characterize the average rate at which nearby trajectories in phase space converge or diverge and therefore provide a useful criterion for dynamical stability. In this work, we develop a general framework for analyzing Lyapunov exponents in stationary spacetimes and extend previous studies beyond circular orbits. For a generic stationary spacetime described by $g_{μν}(r,θ)$, we show that the phase space relevant to linear perturbations is spanned by $(r,p_r,θ,p_θ)$ and the corresponding linear stability matrix has rank four. When the spacetime admits a rank-2 Killing tensor, the linear stability matrix can be reduced to a block-diagonal form, allowing the Lyapunov exponents to be obtained analytically. By imposing the appropriate constraint conditions, the formalism further yields the linear stability matrices and Lyapunov exponents for circular and spherical orbits. The validity of the method is illustrated by several representative examples, including the (inverted) harmonic oscillator, planar Kepler motion, and particle motion in Schwarzschild and Kerr spacetimes. These results provide a unified framework for investigating the stability properties of particle orbits in both classical and relativistic dynamical systems.

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arXiv2026

Scalar wave dark matter imprints on binary black hole mergers: dependence on field mass and density

Dark matter environments can modify binary black hole mergers and imprint their gravitational-wave signals. We perform numerical-relativity simulations of nonspinning binary black holes immersed in complex scalar-field clouds, considering mass ratios $q=1,2,3,$ and $4$ and varying both the dimensionless scalar-field mass $\hat m_Φ=m_ΦM_0$ and initial amplitude $Π_0$, which controls the density. Our initial data keep the scalar energy-density profile and binary geometry unchanged when varying $\hat m_Φ$ at fixed $Π_0$, allowing the dynamical effect of the field mass to be isolated. We find that the scalar environment generally accelerates the merger and significantly modifies the gravitational-wave signal. For unequal-mass binaries, differential scalar-field accretion changes the horizon-mass ratio during inspiral, weakly at low density but substantially at high density, thereby increasing the binary asymmetry before merger. Dense scalar environments suppress the energy and angular momentum carried by gravitational waves. Lighter scalar fields propagate more efficiently to large radii, whereas heavier fields remain more localized and show stronger inward energy transport. Scalar angular-momentum transport is more complex, showing nonmonotonic behavior and even direction reversal near the binary. For unequal-mass systems, gravitational and scalar radiation both carry net linear momentum, and their relative orientation determines whether the recoil is enhanced or suppressed. The largest kick is $2063.6~{\rm km,s^{-1}}$ for $q=2$, $\hat m_Φ=0$, and $Π_0=0.0100$, compared with $137.8~{\rm km,s^{-1}}$ in vacuum. These results show that the scalar-field mass and density jointly control the binary asymmetry, dynamics, radiative channels, and momentum balance.

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arXiv2026

Central charge and black hole entropy for regular extremal black-bounce spacetimes

The Bekenstein-Hawking entropy, proportional to one quarter of the horizon area, is fundamental in black hole thermodynamics and can also be understood via the AdS/CFT correspondence, such as the 3D BTZ black hole and 2D CFT. In this work, we adopt the Kerr/CFT approach to analyze the central charge and black hole entropy for regular extremal black-bounce spacetimes, including the counterparts of the Kerr, Kerr-Newman, and Reissner-Nordström black holes. These spacetimes are free of curvature singularities at $r=0$. We derive the near horizon geometries of these spacetimes and find that they exhibit enhanced symmetry, namely SL$(2,\mathbb{R})\times \mathrm{U}(1)$ or SL$(2,\mathbb{R}) \times \mathrm{SO}(3)$. By imposing appropriate boundary conditions, we analyze their asymptotic symmetry groups, which contain diffeomorphisms as well as the $\mathrm{U}(1)_{\rm gauge}$ symmetry arising from the electromagnetic field. We then extract the central charge from the charge algebra and evaluate the left-moving temperature of the Frolov-Thorne vacuum. It is worth emphasizing that in the black-bounce Kerr-Newman case, the central charge from the electromagnetic contribution vanishes. Furthermore, in the black-bounce Reissner-Nordström case, we uplift the 4D geometry to a 5D configuration by incorporating a $\mathrm{U}(1)$ gauge fiber. Our results show that the microscopic entropy calculated from the Cardy formula is consistent with the Bekenstein-Hawking entropy. This agreement suggests that the Kerr/CFT approach remains valid for certain regular spacetimes without curvature singularities, thereby providing a microscopic statistical understanding of black hole entropy.

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arXiv2026

Evolution and disruption of circular orbits during dynamic black hole scalarization

Dynamical black hole scalarization describes the process by which a ``no-hair" black hole transitions to a scalarized hairy state. This transition significantly alters the spacetime geometry, including the structure of stable circular orbits of the test particles, which are critical for astrophysical observations and tests of gravity. In this work, we employ numerical relativity simulations to model the time-dependent evolution of a vacuum black hole undergoing scalarization. By evolving timelike geodesic equations within the dynamically changing spacetime background, we investigate how the scalarization process impacts initially stable circular orbits. Our results reveal that the growth of the scalar hair destroys the circular nature of these orbits, forcing them to either become eccentric or plunge into the black hole. This orbital destabilization arises from the rapid change of spacetime curvature induced by the scalar field. Our findings provide novel insights into the interplay between scalar fields and black hole dynamics, with significant implications for gravitational-wave signatures, accretion disk stability, and observational tests of extended theories of gravity.

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arXiv2026

Holographic complexity of de Sitter black holes

We investigate holographic complexity within the Schwarzschild-de Sitter (SdS) black hole spacetime. Two distinct de Sitter holography prescriptions are examined: the static patch scheme restricted to the stretched horizon and the de Sitter/Conformal Field Theory (dS/CFT) correspondence scheme defined at asymptotic future and past infinities. We evaluate the Complexity equals Volume (CV) conjecture and extend the analysis to codimension-zero proposals, specifically Complexity equals Spacetime Volume (CV2.0) and Complexity equals Action (CA), through the Wheeler-DeWitt (WDW) patch we construct. The behaviors of the complexity in the static patch holography at late time and in the dS/CFT at infinite spacelike boundary coordinate are studied, respectively. We find that under both the CV and CV2.0 conjectures, the static patch holographic complexity and the dS/CFT holographic complexity consistently exhibit linear growth. Conversely, regarding the CA conjecture, the holographic complexity growth rates for both the static patch and the dS/CFT correspondence vanish. This behavior is attributed to the finiteness of the (regularized) action within the restricted WDW region. Furthermore, we find that, in the limit in which the boundary coordinate is taken to infinity, the complexity growth rate in the static patch prescription coincides with its counterpart in the dS/CFT prescription. This agreement suggests a deeper connection between the two descriptions and may point toward a unified understanding of bulk dynamics in de Sitter holography.

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arXiv2026

Gravitational equal-area law and critical phenomena of cuspy black hole shadow

The formation of a cusp on a black hole shadow is a striking signature of physics beyond the Kerr paradigm. Using the Konoplya-Zhidenko metric, a general parametrized deformation of Kerr black hole, we demonstrate that this morphological change fundamentally alters the shadow's topology with the topological charge flipping from 1 to -1. To analyze this topological transition, we introduce a gravitational equal-area law, analogous to Maxwell's construction in thermodynamics, and identify a critical point for cusp formation. Near this point, we uncover universal behavior characterized by a critical exponent 1/2, which places this gravitational lensing system within the mean-field universality class. These results establish a new framework for testing fundamental physics of black hole shadows, reframing the search for deviations from general relativity as a targeted hunt for a distinct topological and critical phenomenon.

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arXiv2026

The universal topological charge of black hole photon spheres in higher dimensions

A recently developed topological approach offers novel insights into photon spheres, which are fundamental to the formation of black hole shadows. In this study, we extend this topological analysis to higher-dimensional, static, spherically symmetric, and asymptotically flat black holes. By examining the asymptotic properties of the vector field associated with the photon spheres, we demonstrate that their topological charge is consistently -1. This result is a dimensionally independent invariant, guaranteeing the existence of at least one standard (unstable) photon sphere outside the event horizon. We further explore this conclusion by analyzing two distinct regular black hole solutions derived from pure gravity theory, confirming that the topological charge remains -1 irrespective of the spacetime dimension. These results provide a robust and universal characterization of photon spheres in higher-dimensional spacetimes.

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arXiv2026

Enhanced energy extraction via magnetic reconnection in Kerr-AdS spacetime

In this paper, we study the energy extraction from Kerr-AdS black holes following the magnetic reconnection process. The parameter space regions that satisfy the energy extraction condition, as well as the efficiency and power of the extracted energy, are analyzed. The study shows that the presence of a negative cosmological constant extends the range of dominant reconnection radial locations where the energy extraction condition is met, and enables energy extraction even from black holes with relatively low spin. Furthermore, the influence of the negative cosmological constant on energy extraction is modulated by the extent of the dominant reconnection radial region: a more negative cosmological constant enhances the extracted energy, efficiency, and power, particularly for smaller dominant reconnection radii. These results demonstrate that the energy extraction from Kerr-AdS black holes is more favorable than that from their asymptotically flat counterparts. Our results highlight the crucial role of the cosmological constant in energy extraction via magnetic reconnection.

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arXiv2026

A new type of multi-branch periodic orbits in dyonic black holes

We investigate bound timelike periodic orbits in dyonic black hole spacetimes arising from quasi-topological electromagnetism. By varying the coupling parameter $α_1$, we show that the exterior monotonicity of the metric function, rather than the number of horizons, controls the topology of the radial effective potential, which can exhibit either a single well or multiple wells separated by potential barriers. When $f(r)$ is non-monotonic outside the event horizon, the effective potential develops multiple wells, leading to multiple MBO branches and several coexisting periodic-orbit branches with the same rational number $q$. These branches are topologically equivalent but geometrically distinct, because they correspond to different energies or angular momenta, leading to different radial extents and eccentricities. In particular, bound periodic orbits with $E>1$ can occur, and up to three branches may coexist. We also find an inverted radial response: the innermost branch becomes more circular as the energy or angular momentum increases, whereas the outer branches become more eccentric. By contrast, when $f(r)$ is monotonic outside the event horizon, the effective potential has a single well and only one periodic orbit branch exists, even for black holes with multiple horizons. Our results identify metric non-monotonicity as the geometric origin of multi-branch periodic motion and suggest a timelike counterpart to the multiple photon ring signatures of nonstandard black hole geometries.

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arXiv2026

Gravitational partition function under volume constraints

The Euclidean action provides a bridge between gravitational thermodynamics and the partition function. In this work, we further investigate the gravitational partition function under a fixed-volume constraint, generalizing the fixed-volume on-shell geometry in the massless case. Moving beyond this massless configuration, we construct solutions with nonvanishing mass functions, which give rise to a new class of volume-constrained Euclidean geometries (VCEGs). These geometries possess both a boundary and a horizon. However, closer inspection indicates that the boundary is not intrinsic, but rather artificially introduced and can be extended, leading to the extended volume-constrained Euclidean geometries (ECVEGs). The ECVEGs contain two horizons, each generically associated with a conical singularity. Their Euclidean action is given by one quarter of the sum of the areas of the two horizons. In general, the conical singularities at the two horizons cannot be simultaneously eliminated, except at a critical mass $m = m^*$, which defines the critical ECVEG. Configurations with unavoidable conical singularities are naturally interpreted as constrained gravitational instantons. An analysis of their contributions to the partition function, together with their topological properties, reveals a close analogy between the ECVEGs and the Euclidean Schwarzschild--de Sitter static patch. This suggests that the volume constraint effectively plays a role analogous to that of a cosmological constant in semiclassical quantum gravity.

hep-th↗

arXiv2026

Interior geometry of black holes as a probe of first-order phase transition

Traditional diagnostics of black hole phase transitions rely on thermodynamic quantities defined at the event horizon or asymptotic boundary. Here, we demonstrate that the near-singularity geometry offers a sharp, independent probe of both first-order phase transitions and supercritical crossover. For scalarized AdS black holes exhibiting a first-order phase transition, the Kasner exponent $p_t$, which characterizes the approach to the singularity, undergoes a dramatic transformation. On one side of the transition, $p_t$ oscillates strongly with temperature, reflecting violent interior dynamics. On the other side, it becomes a smooth, monotonically varying function. These two distinct behaviors converge as the critical point is approached. Beyond the critical point, in the supercritical region, $p_t(T)$ develops a distinct extremum, defining a Kasner crossover line that is entirely independent of traditional thermodynamic (Widom line) or dynamic (Frenkel line) criteria. Our work establishes the near geometry of singularity of scalarized black hole as a novel class of diagnostics for phase transitions, revealing that a change in the macroscopic thermodynamic state fundamentally reshapes the deepest interior structure of spacetime.

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arXiv2026

Unifying topological, geometric, and complex classifications of black hole thermodynamics

Black hole thermodynamics has recently witnessed three distinct classification schemes: based on local geometric properties of the temperature function, global topological invariants, and Riemann surface foliations in the complex plane. We show that these schemes can be precisely mapped onto one another in the real domain via two dictionaries: one linking thermal stability to the monotonicity of the temperature curve, and the other connecting the number of black hole states to the foliation number of a Riemann surface. The number of extremal points of the temperature curve determines the classification in all three frameworks, tracing this unification to the critical point structure of the black hole solution space. As an illustration, several black holes demonstrate how counting extrema yields topological invariants and phase transition information. This unified framework simplifies black hole thermodynamic analysis and provides a foundation for exploring more complex black holes.

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arXiv2026

Phase transitions in scalarized topological AdS black holes

We investigate the behavior of black hole scalarization induced by a charged scalar field in the extended phase space of the asymptotic AdS spacetime with three distinct horizon topologies. The results indicate that in all three cases, the charged black hole spacetime undergoes scalarization at low temperatures. Notably, the spherical topology is unique in that its domain of scalarization theoretically extends to much higher temperatures under low pressure in the extended phase space. Moreover, the scalarization process in the spherical case exhibits complex phase transition behaviors without additional non-linear terms, which are similar to those in the planar and hyperbolic topologies with the assistance of non-linear terms. With increasing pressure in the extended phase space, the condensate of the scalarization in all three cases undergoes a transition from the first-order style to a cave-of-wind style. This study provides deeper insight into the zeroth-order phase transition during black hole scalarization and reveals the complete phase structure of black holes in the extended phase space.

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arXiv2026

Black Hole Entropy Beyond the Wald Term in Nonminimally Coupled Gravity: A Covariant Phase Space Decomposition

We study the entropy of static, spherically symmetric black holes in diffeomorphism-invariant theories with nonminimal matter--curvature couplings, using the covariant phase space formalism. For regular bifurcate Killing horizons, the Iyer--Wald construction gives the standard Wald entropy. If a matter field cannot be smoothly extended to the regular bifurcation surface, however, the entropy-sector horizon surface charge variation can contain finite contributions that are not included in the Wald entropy density. In the representative obtained by directly varying the action, and after ordinary non-gravitational boundary terms have been separated into the work sector, we decompose the entropy entering the first law of black hole thermodynamics as $\SH=\SW+\Sone+\DeltaS$. Here $\SW$ is the Wald entropy, $\Sone$ is the non-Wald part of the entropy-sector Noether charge, and $\DeltaS$ is the remaining integrable part of the entropy-sector horizon surface charge variation. Applying this criterion to Kalb--Ramond, bumblebee, and extended Gauss--Bonnet black holes, we find that the regular Kalb--Ramond branch has $\SH=\SW$, the bumblebee branches yield either $\Sone=0$ with $\DeltaS\neq0$ or a cancellation between $\Sone$ and $\DeltaS$, and the Weyl-vector extended Gauss--Bonnet examples require both corrections. This provides a direct test of whether the Wald density is sufficient or whether the full horizon surface charge variation is required.

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arXiv2026

Topological perspective on bulk boundary thermodynamic equivalence

We establish an exact duality between the extended thermodynamics of five-dimensional charged Gauss-Bonnet AdS black holes and the thermodynamic framework of the dual boundary conformal field theory (CFT). The thermodynamics of the dual CFT involves two central charges originating from the trace anomaly. We demonstrate a precise correspondence between the extended first laws on the bulk and boundary sides. Moreover, the topological charges of the CFT thermodynamics, associated with the phase transition and critical point, coincide with those of the corresponding bulk black hole.

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