arXiv subjects

Jia-Zhou Liu

Publications and source records attributed to Jia-Zhou Liu.

9 recordsLinked to original sources

arXiv2026

Radial Stress and the Innermost Stable Circular Orbit of a Bardeen Black Hole in a Dark Matter Halo: A First-Order Response Criterion

A dark matter density profile alone does not determine the spacetime around a black hole; the radial stress must be prescribed separately and governs the strong-field orbital response. We study a Bardeen black hole in a Hernquist halo through three spherical models sharing the same density, mass function, and cutoff but differing in radial stress: a halo with $p_r^{\mathrm{DM}}=-ρ_{\mathrm{DM}}$, its truncated form, and a truncated Einstein cluster with $p_r^{\mathrm{DM}}=0$. Treating the halo as a small perturbation, we derive a first-order criterion for the leading innermost stable circular orbit shift, $C_λ=C_ρ+λC_p$. The two truncated closures shift this orbit in opposite directions for the Hernquist profile, and unexpanded calculations for five density profiles confirm the predicted signs. Checks using a Hayward background and a published Dehnen-halo result show that the criterion is not restricted to the Bardeen-Hernquist system. A continuous stress interpolation identifies a critical closure at which the leading shift vanishes. For a representative four-year extreme-mass-ratio inspiral, changing the radial stress at fixed density and cutoff produces a phase difference of several radians in a leading-order adiabatic treatment.

gr-qc↗

arXiv2026

Charged Black Holes with a Lorentz--Violating Kalb--Ramond Background

We investigate exact static, spherically symmetric electrically charged black hole solutions in a gravitational theory with spontaneous Lorentz-symmetry breaking induced by a background Kalb--Ramond field. In contrast to previous analyses that retained only one nonminimal curvature coupling, we include the combined effects of the two independent nonminimal curvature couplings and obtain charged black hole solutions both with and without a cosmological constant. Using the Iyer--Wald covariant phase-space formalism, we derive the corrected thermodynamic quantities and analyze the Joule--Thomson expansion, including the inversion curve and the cooling/heating regions. We further apply the topological approach to black hole thermodynamics to characterize the van der Waals-like phase transition and show how the thermodynamic critical temperature and pressure are encoded in the corresponding topological defect curve. These results clarify the thermodynamic and topological signatures of electrically charged black holes in gravity with a Lorentz-violating Kalb--Ramond background.

gr-qc↗

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.

gr-qc↗

arXiv2026

Exact Black Hole Solutions in Bumblebee Gravity with Lightlike or Spacelike VEVS

Motivated by recent developments in Lorentz-violating theories of gravity, we obtain new black hole solutions within the framework of bumblebee gravity, where the bumblebee vector field possesses two independent nonzero components and acquires either a lightlike or spacelike vacuum expectation value. Within this framework, we derive new Schwarzschild-like and Schwarzschild-(A)dS-like black hole solutions. By further incorporating a nonminimally coupled electromagnetic field, we generalize these to new charged black hole solutions. These solutions extend previous results by including additional Lorentz-violating parameters. A key finding is that even for lightlike vacuum expectation values, the black hole solutions exhibit distinct corrections from Lorentz violation. Furthermore, we present a preliminary analysis of their thermodynamic properties. Similar to previous studies that reported a discrepancy between the black hole entropy and the Wald entropy in bumblebee gravity with spacelike vacuum expectation values, our solutions in the spacelike case exhibit the same behavior. In contrast, for the lightlike case considered here, the two entropies coincide.

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arXiv2026

D-dimensional black holes in extended Gauss-Bonnet gravity

In this work, we present charged spherically symmetric anti-de Sitter black hole solutions in $d$ dimensions ($d \geq 5$) within the framework of extended Gauss--Bonnet gravity. Moreover, by employing dimensional regularization of the extended Gauss--Bonnet term, we further obtain charged anti-de Sitter black hole solutions in three- and four-dimensional spacetimes. Furthermore, we also obtain a three-dimensional rotating black hole solution in a special case. These solutions contain an independent vector-sector parameter and exhibit different horizon structures compared with the standard charged Gauss--Bonnet branch. For the charged solutions, we also give a concise Iyer-Wald thermodynamic analysis. Nonetheless, their asymptotic behavior at spatial infinity remains consistent with that of the corresponding black holes in general relativity.

gr-qc↗

arXiv2026

Dyonic Black Holes in Lorentz-Violating Gravity with a Background Kalb--Ramond Field

By introducing a nonminimal coupling between the Kalb--Ramond field and the electromagnetic field, we construct an exact four-dimensional static, spherically symmetric dyonic black hole solution in Lorentz-violating gravity with a background Kalb--Ramond field. The curvature invariants show that the spacetime retains a genuine curvature singularity at $r=0$. We then analyze the geodesic motion of null and timelike particles and obtain the photon-sphere radius, the shadow radius, and the innermost stable circular orbit, demonstrating that both the Lorentz-violating parameter and the dyonic charges can appreciably modify the shadow size and the domain of stable circular motion. In the extended phase space, we derive the thermodynamic quantities and verify the first law of black hole thermodynamics together with the Smarr relation. The system also exhibits a first-order phase transition between small and large black holes, and its phase structure is strongly influenced by the Lorentz-violating parameter and the dyonic charges.

gr-qc↗

arXiv2026

Quasinormal modes of a charged spherically symmetric black hole in bumblebee gravity

Recently, exact charged spherically symmetric black hole solutions within the framework of bumblebee gravity have been obtained, where the Lorentz symmetry is spontaneously broken due to the nonvanishing vacuum expectation value of the bumblebee field. In this work, we investigate the quasinormal modes of this black hole. We compute the quasinormal frequencies corresponding to the scalar perturbation and the gravito-electromagnetic coupled perturbation using both the continued fraction method and the asymptotic iteration method. A detailed comparison of the results obtained from the two approaches is presented to evaluate their accuracy and efficiency in this Lorentz-violating background.

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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

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.

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