arXiv subjects

Xiao-Mei Kuang

Publications and source records attributed to Xiao-Mei Kuang.

At least 19 recordsLinked to original sources

arXiv2026

Resonant bound orbits and kludge waveforms in rotating Konoplya-Zhidenko black hole spacetime

We investigate timelike bound motion, resonant periodic orbits, and their gravitational-wave signatures in the rotating Konoplya-Zhidenko (KZ) black hole spacetime. Using the separability of the Hamilton-Jacobi equation, we parameterize eccentric and inclined bound orbits by $(p,e,z_1)$, derive the corresponding constants of motion $(E,L_z,Q)$, and use the orbital frequencies to identify resonant configurations. We study a range of resonances, including radial-polar resonances of inclined orbits and radial-azimuthal resonances of equatorial eccentric orbits. We further construct physically scaled quadrupole-kludge waveforms for representative equatorial resonant orbits and analyze their frequency-domain characteristics. Our results show that the KZ deformation shifts the resonance locations and modifies both the orbital trajectories and the resulting gravitational-wave signals. The corresponding characteristic strain lies predominantly in the millihertz band, placing these signals in the frequency range relevant to space-based gravitational wave detectors.

gr-qc↗

arXiv2026

Detecting Lorentz-violation induced by a tensor field with S-star's motion around Sgr A*

Testing Lorentz symmetry in strong gravitational fields provides a unique probe of extensions to standard model. The orbiting motions of the S-stars around the supermassive black hole Sgr~A* provide a natural laboratory for such tests. In this paper, we analyze the S2 orbital data focusing on a static and spherically symmetric black hole within Kalb--Ramond gravity, where the deviations from general relativity are encoded in a single Lorentz-violating parameter $\ell$ introduced by the Kalb--Ramond tensor field. Using a full 14-dimensional Markov Chain Monte Carlo analysis under uniform and Gaussian priors, we obtain $\ell = {1.60 \times 10^{-5}}^{+1.38 \times 10^{-4}}_{-1.76 \times 10^{-4}} $ and $\ell = {-1.02 \times 10^{-5}}^{+1.26 \times 10^{-4}}_{-1.19 \times 10^{-4}} $ at $1σ$ confidence level, respectively. These constraints are about three orders of magnitude tighter than those from Event Horizon Telescope imaging of Sgr~A*. We also perform MCMC simulation by fitting data of S38 and S55 stars, as well as their joint analysis. Our results show that the best fit values of $\ell$ in all simulations are always of $10^{-5}$ order, but S2 star provides the most stringent constraints on the parameters because S2 star has higher precision observational data comparing to the fewer public data for other two stars.

gr-qc↗

arXiv2026

Mapping Quasi-Periodic Oscillations to Lyapunov Exponent across Black Hole Thermodynamic Phase Transitions

We investigate the thermodynamic phase structure of a nonminimally coupled magnetic AdS black hole through the dynamics of timelike particles. The free energy analysis reveals a Van der Waalslike phase transition characterized by small, intermediate, and large black hole phases. We show that both the Lyapunov exponent of unstable circular orbits and the quasi-periodic oscillation (QPO) frequencies associated with stable circular orbits exhibit clear signatures of underlying thermodynamic phase structure, including first order and critical phase transitions. More importantly, we establish a QPO-Lyapunov exponent mapping and demonstrate that the resulting relation inherits the same thermodynamic branch structure. Although the Lyapunov exponent and QPO frequencies originate from unstable and stable circular orbits, respectively, their correspondence emerges from the common black hole spacetime geometry and remains valid even in the absence of phase transitions. Our results reveal an unexplored connection among orbital instability, QPO phenomenology, and black hole thermodynamics, suggesting a potential observational route for probing chaotic orbital dynamics and thermodynamic phases through QPO measurements.

gr-qc↗

arXiv2026

On the mapping between bound states and black hole quasinormal modes via analytic continuation: a spectral instability perspective

In this work, we investigate the relation between bound states and quasinormal modes within black hole perturbation theory in the context of spectral instability. Our analysis indicates that the reliability of such spectral mapping stretches beyond the domain of validity of the analytic continuation employed to connect the perturbative bound-state problem to the corresponding open-system dynamics. However, for the numerical scheme proposed by Völkel to work, the transformations of the metric parameters must be carried out in a region where the underlying Taylor expansion is convergent. As analytically accessible explicit examples, we explore the perturbed delta-function and Pöschl-Teller potential barriers. For the latter, we construct two distinct perturbative setups for which the convergence of the series expansion involved in the perturbation theory can be rigorously controlled. When the deformation is placed near the potential's extremum, the resulting corrections to the bound-state energies can be analytically continued to yield perturbed quasinormal frequencies, in agreement with known semi-analytic results. In contrast, when the perturbation is localized asymptotically far from the compact object, the bound states are only mildly modified and are accurately described by a perturbative expansion to the first order. However, the associated analytic continuation yields a strongly deformed spectrum that shows no clear connection to the quasinormal modes. These findings contribute to the effort to scrutinize the conditions under which bound states faithfully encode quasinormal spectra and to shed light on the underlying physics of black hole spectral instability.

gr-qc↗

arXiv2026

Soft cutoffs in the covariant phase space of dynamical reference frames

We construct covariant theories incorporating fluctuating boundaries and soft cutoffs by introducing dynamical reference frames (DRFs). This framework generalizes the covariant action from a hard-cutoff to a soft-cutoff formulation, utilizing smearing functions and their corresponding operator expansions. This generalization initially leads to a loss of diffeomorphism covariance, which is recovered solely by restricting the DRFs, along with both their associated and linear MCFs, to specific forms, and by imposing suitable boundary conditions on the smearing functions. Satisfying these conditions restores covariance in relational spacetime, thereby enabling the consistent definition of subsystems. Within the covariant phase space formalism, we derive the charges of the soft-cutoff theory while explicitly addressing the inherent ambiguities arising from the boundary Lagrangian. We demonstrate that introducing an additional pointwise dependence is essential to resolve these ambiguities and ensure the integrability of the charges, even under fluctuating boundary conditions. Finally, in the context of General Relativity (GR), we establish the conditions under which holographic renormalization results at the asymptotic boundary coincide with the Noether charges derived from our soft-cutoff procedure.

hep-th↗

arXiv2026

The bound orbits and gravitational waveforms of timelike particles around renormalization group improved Kerr black holes

In this article, we investigate the bound orbits of the timelike particles and the gravitational waveforms emitted from these orbits around a renormalization group improved Kerr black hole in the framework of the asymptotic safety approach. The running Newton coupling in the metric is characterized by two free quantum parameters $(ω,\,γ)$ arsing from the non-perturbative renormalization group theory and the appropriate cutoff identification, respectively. As expected, the radii of the horizon, the marginally bound orbits and the innermost stable orbit are all decrease as the quantum parameters increase. Under the extreme mass-ratio inspirals approximation the deviation of gravitational waveforms radiated by the periodic orbits from those in the classical Kerr background increases with the two quantum parameter. However, this effect is much smaller in the retrograde case compared to the prograde case. Especially, by comparing the characteristic strain of those gravitational wave with the sensitivity curve of several potential detectors, we find that their characteristic frequencies can fall within the sensitivity ranges of several planned gravitational wave observatories, suggesting that such signals may be detectable with sufficient instrumental sensitivity.

gr-qc↗

arXiv2026

QNM families: classification and competition

The perturbation spectra of black holes beyond standard vacuum black hole solutions within generalrelativity (GR) may exhibit complex structures with long-lived modes. This usually generates echolikemodulations on the ringdown signal, which typically originate from modified boundary conditionsassociated with exotic compact objects. Recent studies also reveal that they can instead arise from themultipeaked structure of the perturbation potential. However, while some case-by-case studies have beencarried out, a framework for understanding the internal structure of such spectra, the physical nature ofdifferent mode families, and their dynamical excitation remains to be fully systematized. In this paper,we address this issue by proposing a potential methodology that combines frequency-domainclassification with time-domain analysis, using a hairy Schwarzschild black hole that admits adouble-peak perturbative potential as a theoretical platform. Our analysis of the quasinormal modespectrum identifies two distinct families of modes: the photon sphere (PS) family, arising fromdelocalized scattering resonances, and the echo family, corresponding to highly localized quasiboundstates. We then develop a windowed energy analysis framework in the time domain, which discloses adynamic competition for dominance between these families. In particular, our results explicitly showthat this competition is sensitive to the properties of the initial perturbation source, and that higher-overtone echo modes can dominate in the observed signal, which are in contrast to the standard PS modein GR. This study establishes the dynamic evolution of this energy competition as a new observationalsignature for probing new physics and further motivates a supplemental framework for analyzing long-lived ringdown signals.

gr-qc↗

arXiv2026

Geodesic dynamics and multi-inclination images of a non-minimally coupled black hole with a thin accretion disk

In this paper, we investigate the optical properties of a black hole in non-minimal Einstein-Yang-Mills theory, illuminated by a thin accretion disk. In our setup, matter follows stable circular orbits outside the innermost stable circular orbit (ISCO), while inside the ISCO, it rapidly plunges into the black hole. By analyzing the orbital dynamics of massive and massless particles, we find that the properties of both the ISCO and the photon sphere significantly depend on the non-minimal coupling parameter. Moreover, compared with the Schwarzschild and Reissner-Nordström black holes, the non-minimal coupling extends the range of the impact parameter and slightly enhances the redshift effect in the images. Additionally, due to the significant influence of the non-minimal coupling parameter on the event horizon, the observed intensity of this black hole image under the selected emission model ultimately turns out to be weaker than that of the other two types of black holes, regardless of the inclination angle between the accretion disk and observation planes.

gr-qc↗

arXiv2026

Using precession and quasiperiodic oscillations to constrain a rotating regular black hole

In this paper, we investigate the frame-dragging effect on an accretion disk and test gyroscope orbiting around a rotating regular black hole with a Minkowski core. Firstly, we perturb a bound timelike circular orbit around the black hole, and analyze the periastron precession and Lense-Thirring (LT) precession frequencies of the orbit's epicyclic oscillations. Since these epicyclic oscillations can be used to explain the quasiperiodic oscillations (QPOs) phenomena of the accretion disc around this rotating regular black hole, we then employ the Markov Chain Monte Carlo (MCMC) simulation to fit our theoretical results with five QPOs events (GRO J1655-40, GRS 1915+105, XTE J1859+226, H1743-322 and XTE J1550-564). The simulations give the relevant physical parameter space of the black hole, including the characteristic radius $r$, the mass related parameter $M$, the spinning parameter $a$ and the quantum gravity effect $α$. The results give the constraint on the quantum effect parameter, with an upper limit $α/M^{2/3} < 0.60$ at the $95\%$ C.L., which is tighter than $<0.7014$ in our pervious study within static case. Then, we theoretically explore the LT precession frequency, geodetic precession frequency, and the general spin precession frequency of a test gyro attached to a stationary observer in this black hole background. We find that the quantum gravity effect suppresses the precession frequencies comparing against those in Kerr black hole, further providing a theoretical diagnostic of the potential quantum gravity effect.

gr-qc↗

arXiv2026

Precessions and parameter constraints from quasiperiodic oscillations in a rotating charged black hole

We investigate quasi-periodic oscillations (QPOs) as a diagnostic tool for probing frame-dragging effects and accretion disk physics in the spacetime of a rotating regular magnetic black hole (BH). Specifically, we analyze the precession of bound orbits and the epicyclic oscillations of test particles under small perturbations in the equatorial plane. We demonstrate how the BH nonminimal coupling parameter (lambda/M^4) and dimensionless magnetic charge (Q/M) significantly influence the three fundamental epicyclic frequencies. By applying the relativistic precession model and employing Markov Chain Monte Carlo simulations (MCMC), we constrain the BH characteristic parameters, including mass, spin, magnetic charge, and nonminimal coupling, using observational QPO data from five X-ray binaries: GRO J1655-40, XTE J1859+226, H1743-322, XTE J1550-564, and GRS 1915+105. Furthermore, we examine the Lense-Thirring, geodetic, and general spin precession frequencies of a test gyroscope attached to a stationary observer around the black hole. Our theoretical results indicate that the regular charged black hole suppresses these precession frequencies compared with the Kerr black hole case.

gr-qc↗

arXiv2026

Probing a Lorentz-violating parameter from orbital precession of the S2 star around the galactic centre supermassive black hole

Testing Lorentz symmetry in strong gravitational fields provides a promising probe of extensions to general relativity. The supermassive black hole Sgr~A* and the orbit of the S-stars offer a laboratory for such tests in a regime beyond weak field limit. We analyze the S2 orbital data focusing on the Schwarzschild-like black hole within bumblebee gravity, where deviations from general relativity are encoded in a single Lorentz-violating parameter $\ell$. Using a full 14-dimensional Markov Chain Monte Carlo analysis under uniform and Gaussian priors, we obtain $\ell = {-8.01 \times 10^{-5}}^{+2.77 \times 10^{-4}}_{-2.09 \times 10^{-4}} $ and $\ell = {1.00 \times 10^{-5}}^{+2.90 \times 10^{-4}}_{-2.91 \times 10^{-4}} $ at $1σ$ confidence level, respectively. These constraints are about three orders of magnitude tighter than those from Event Horizon Telescope imaging of Sgr~A*.

gr-qc↗

arXiv2026

On Hyperboloidal Foliations in the Study of Black Hole Quasinormal Modes

In this work, we demonstrate that the hyperboloidal foliation technique, applied to the study of black hole quasinormal modes, where the spatial boundary is shifted from spacelike infinity to the future event horizon and null infinity, is effectively equivalent to the continued fraction approach, in which the asymptotic wave function typically diverges at both ends of spatial infinity. Specifically, a given hyperboloidal slicing, corresponding to a particular choice of coordinates, always uniquely determines a scheme for extracting the asymptotic form of the wave function at the spatial boundary. Owing to the mathematical equivalence, it follows that the efficiency and precision observed using the hyperboloidal approach should be attributed, not to avoiding the pathological behavior at the spatial boundaries, but primarily to other factors, such as the use of Chebyshev grids.

gr-qc↗

arXiv2025

Exploring black holes with multiple photon spheres by interferometric signatures

In this paper, we investigate the interferometric signatures of hairy Schwarzschild black holes (hSBHs) that have either single or double photon spheres. Our interest mainly stems from two considerations: (i) the photon ring structure in black hole images produces strong and universal interferometric signatures on long baselines, enabling precision measurements of black hole parameters and testing gravitational theory; (ii) the hSBH describes the deformation of standard Schwarzschild black hole (SBH) induced by additional sources, and they can feature double photon spheres within certain parameter regimes. Using both analytical and numerical methods, we find that for a hSBH with a single photon sphere, the complex visibility amplitude of the image exhibits damped oscillations. A similar behavior appears in the double photon sphere case when the inner photon sphere has lower effective potential than the outer one, as the photons near the inner photon sphere remain trapped by gravity. However, when the inner potential is higher, a beat pattern rises. Our findings reveal that the complex visibility amplitude can encode the signature of the photon sphere structure of the central black hole.

gr-qc↗

arXiv2025

Wiggling boundary and corner edge modes in JT gravity with defects

We study the gravitational edge modes (GrEMs) and gauge edge modes (GaEMs) in Jackiw-Teitelboim (JT) gravity on a wiggling boundary. The wiggling effect manifests as a series of spacetime topological and bulk constraints for both conical and wormhole defect solutions. For the conical defect solution, we employ the generalized Fefferman-Graham (F-G) gauge to extend the boundary action, allowing for non-constant temperature and horizon position. We find that the infrared behavior of this boundary action is determined by the local dynamics of the temperature and horizon. For the wormhole defect solution, the boundary action can, in special cases, be described by a field with variable mass subject to a constant external force. We classify this corner system as a first-class constrained system influenced by field decomposition, confirming that the physical degrees of freedom are determined by constraints from the wiggling boundary information. We find that GrEMs and GaEMs can be linked at the corners by imposing additional constraints. Additionally, we show that the ``parallelogram'' composed of corner variables exhibits discreteness under a unitary representation. Finally, we explore that information from extrinsic vectors can be packaged into the GaEMs via a Maurer-Cartan form, revealing the boundary degrees of freedom as two copies of the $\mathfrak{sl}(2,\mathbb{R})$ algebra. By separating pure gauge transformations, we identify the gluing condition for gauge invariance and the corresponding integrable charges.

hep-th↗

arXiv2025

Parameter constraints on Horndeski rotating black hole through quasiperiodic oscillations

In this paper, we perform small perturbations around the circular timelike orbit in the equatorial plane of the Horndeski rotating black hole, and analyze the effects of Horndeski hair on the three fundamental frequencies of the epicyclic oscillations. Since this operation can model the quasiperiodic oscillations (QPOs) phenomena of the surrounding accretion disc, we then employ the MCMC simulation to fit the theoretical results with three QPO events, including GRO J1655-40, XTE J1859+226 and H1743-322, and constrain the characteristic radius $r$, black hole mass $M$ and spinning parameter $a$, and the Horndeski hair parameter $h$. Our constraint on the Horndeski hair parameter is much tighter than QPOs simulation from the existed accretion models, suggesting slight deviation from classical Kerr black hole.

gr-qc↗

arXiv2025

The shadow and quasinormal modes of the asymptotically flat hairy black holes with a dilaton potential

In this article, the shadow and the quasinormal modes (QNMs) of an exact asymptotically flat hairy electrically charged black hole solution with a dilaton potential are investigated. Using the {constraint} equation among the integration constant $η$ of the gravitational field, the mass $M$, the electric charge $Q$ and the coupling constant $ν$ between the $U(1)$ field and the dilaton field, we find that the shadow radii, the Lyapunov exponent $λ$ and the coordinate angular velocity $Ω_{c}$ only significantly affected by $ν$ if the $Q$ is close to the extremal value, especially when $ν$ approaches to one. Furthermore, the QNMs are numerically computed by using the Hatsuda method and verify with the higher-order WKB approximations with the Padé summation. We find that the QNMs are close to that of the low energy limit of the string theory when $ν$ is large enough. In the eikonal limit, the real and imaginary parts are proved to be given by $Ω_{c}$ and $λ$, respectively.

gr-qc↗

arXiv2025

Gauge Symmetries, Exact Symmetries and Conserved Charges in Minimal Massive Gravity

In this paper, we investigate a three-dimensional gravitational model known as Minimal Massive Gravity (MMG), which includes an auxiliary field, using the covariant phase space method. Our analysis reveals the presence of three gauge symmetries whose algebras close via field recombination and parameter classification within this framework. Upon incorporating these additional symmetries within a specific limit of parameters, we find that the Kosmann derivative should be replaced by a novel transformation compatible with Wald's approach, which establishes a new mechanism for generating exact symmetries and constructing their corresponding conserved charge in theories with auxiliary fields, extending beyond standard methods. However, this transformation does not yield closed algebras on the space of fundamental fields. We find that this corresponds to a Lorentz vector that characterizes the approximate completeness of translation symmetry. As a result, we obtain a gauge invariant charge at a certain limit of parameters, which emerges as a nontrivial combination of the diffeomorphism charge and integrable gauge charges.

hep-th↗

arXiv2025

Quantum fluctuation on the worldsheet of probe string in BTZ black hole

In this paper, we investigate the second-order normal quantum fluctuation on the world-sheet of a probe string in the Bañados-Teitelboim-Zanelli (BTZ) black hole. These fluctuations is treated as the projection of Hawking radiation on the worldsheet and indeed modify the action growth of the string. Then in the string field theory/boundary conformal field theory framework, via the boundary vertex operator we study the correlation function of the Schrödinger functional of excited fields on the world-sheet and further extract the field's formula. Our study could shed light on the potential connection between complexity growth and correlation function.

hep-th↗