arXiv subjects

Yu-Xiao Liu

Publications and source records attributed to Yu-Xiao Liu.

At least 55 records · Page 3Linked to original sources

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.

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.

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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.

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arXiv2025

Quasinormal modes of thick branes in $f(R)$ gravity

We systematically investigate the quasinormal modes of thick branes in $f(R)$ gravity by numerically solving the Schrödinger-like perturbation equation of gravitational perturbations. To ensure the reliability of the results, we employ three complementary methods: the asymptotic iteration method, the direct integration of the wave equation, and the time-domain numerical evolution. We analyze how the model parameters influence the shape of the effective potential of gravitational perturbations and find that the structure of the potential barrier plays a significant role in shaping the quasinormal frequency spectrum. The results obtained from the three methods exhibit strong consistency, thereby ensuring the reliability of the calculations. In particular, the real parts of the quasinormal frequencies exhibit an approximately arithmetic progression, suggesting that the quasi-localized states can be understood as resonances between the barriers.

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arXiv2025

Gravitational Wave Detection Based on Gravitomagnetic Effects

In this paper, we explore the feasibility of detecting gravitomagnetic effects generated by gravitational waves, by monitoring the relative orientation of the angular momentum vectors of test particles. We analyze the response of the relative angular momentum direction to all six polarization modes of gravitational waves and estimate the magnitude of its variation during gravitational wave events. Our findings indicate that when test particles possess magnetic moments, applying an external magnetic field of appropriate strength can induce resonant precession of the angular momentum direction under the influence of gravitational waves. This resonance may significantly amplify the gravitational wave signal, potentially enabling its detection with future gyroscope-based detectors. Such detectors would complement existing gravitational wave observatories that rely on gravitoelectric effects.

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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.

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arXiv2025

Gravitational wave cosmology

Gravitational waves (GWs) originating from cosmological sources offer direct insights into the physics of the primordial Universe, the fundamental nature of gravity, and the cosmic expansion of the Universe. In this review paper, we present a comprehensive overview of our recent advances in GW cosmology, supported by the national key research and development program of China, focusing on cosmological GW sources and their implications for fundamental physics and cosmology. We first discuss the generation mechanisms and characteristics of stochastic gravitational wave backgrounds generated by physical processes occurred in the early Universe, including those from inflation, phase transitions, and topological defects, and summarize current and possible future constraints from pulsar timing array and space-based detectors. Next, we explore the formation and observational prospects of primordial black holes as GW sources and their potential connection to dark matter. We then analyze how GWs are affected by large-scale structure, cosmological perturbations, and possible modifications of gravity on GW propagation, and how these effects can be used to test fundamental symmetry of gravity. Finally, we discuss the application of GW standard sirens in measuring the Hubble constant, the expansion history, and dark energy parameters, including their combination with electromagnetic observations. These topics together show how GW observations, especially with upcoming space-based detectors, such as LISA, Taiji, and Tianqin, can provide new information about the physics of the early Universe, cosmological evolution, and the nature of gravity.

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arXiv2025

Complexity equals anything for multi-horizon black holes

We investigate the ``complexity equals anything" proposal with codimension-one and codimension-zero gravitational observables for multi-horizon black holes, using the Bardeen-AdS class black hole as an example. In particular, we compare the results with the ``complexity equals volume" (CV) proposal and find that the ``complexity equals anything" ($\mathcal{C}_{\text{gen}}$) enables the probing of a more complete black hole interior, that is, all spacetime regions where the blackening factor $f(r)<0$. This is the advantage brought by the flexibility of this holographic complexity conjecture. In addition, we compute the complexity derived from various geometric quantities and show that these constructions can effectively differentiate the distinct interior regions of the black hole.

hep-th↗

arXiv2025

New gravitational wave polarization modes in the torsionless spacetime

In this study, we investigate the polarization properties of gravitational waves within a torsionless spacetime framework, as described by the Palatini formalism. Our analysis uncovers the presence of two novel polarization modes, referred to as shear modes, which extend beyond the traditional set of six modes in a four-dimensional Riemannian spacetime. These shear modes, uniquely driven by vector degrees of freedom associated with non-metricity, are classified as vector modes, and their detection provides a unique opportunity to explore the fundamental structure of spacetime and to test gravity theories. These modes extend the standard gravitational wave polarization paradigm and provide novel observational signatures for gravitational wave detectors.

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arXiv2025

Quasinormal modes of an electrically charged Kalb-Ramond black hole

Lorentz violation serves as a significant feature in many modified theories of gravity. In particular, spontaneous Lorentz violation induced by the Kalb-Ramond field has attracted considerable attention. Recently, an electrically charged black hole solution within the Kalb-Ramond framework was proposed. In this study, we investigate the quasinormal modes of the resulting ``undecouplable'' system using both the matrix-valued continued fraction method and the matrix-valued direct integration method. Additionally, we develop a new approach to distinguish between different modes in such ``undecouplable'' systems. An error analysis is performed, and the influence of Lorentz violation on the fundamental quasinormal modes is systematically analyzed within a suitable parameter range.

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arXiv2025

Constraints on quantum Oppenheimer-Snyder black holes with eccentric extreme mass-ratio inspirals

We investigate the potential of extreme mass-ratio inspirals to constrain quantum Oppenheimer-Snyder black holes within the framework of loop quantum gravity. We consider a stellar-mass object orbiting a supermassive Oppenheimer-Snyder black hole in an equatorial eccentric trajectory. To explore the dynamical behavior of the system, we analyze its orbital evolution under gravitational radiation within the adiabatic approximation and the mass-quadrupole formula for different initial orbital configurations. Our results show that the quantum correction parameter $\hatα$ slows down the evolution of the orbital semi-latus rectum and eccentricity. We then employ the numerical kludge method to generate the corresponding time-domain gravitational waveforms. To assess detectability, we include Doppler modulation due to the motion of space-based detectors and compute the frequency-domain characteristic strain. By evaluating mismatches between response signals for different values of $\hatα$, we show that even small corrections $(\hatα \sim 10^{-5})$ produce distinguishable effects. Our analysis suggests that future space-based detectors such as LISA can probe quantum gravitational corrections in the strong-field regime and place constraints significantly stronger than those from black hole shadow observations.

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arXiv2025

Using normal to find abnormal: AI-based anomaly detection in gravitational wave data

The detection and classification of anomalies in gravitational wave data plays a critical role in improving the sensitivity of searches for signals of astrophysical origins. We present ABNORMAL (AI Based Nonstationarity Observer for Resectioning and Marking AnomaLies), a deep neural network (DNN) model for anomaly detection that is trained exclusively on simulated Gaussian noise. By removing dependence on real data for training, the method resolves a circular paradox in anomaly detection: training on real data implicitly involves prior segregation of stationary from non-stationary data but this is not possible unless all anomalies are detected first. ABNORMAL is an autoencoder-based DNN, commonly used in anomaly detection, with the key innovation that it is trained to predict statistical features of noise rather than reconstructing the noise time series themselves. The statistical features are obtained by applying Gabor and Wavelet filter banks, which implement time-frequency analysis, and are subsequently combined through multi-view fusion using a dual-path architecture. We quantify the performance of our method on simulated and real LIGO data. Application to data from the O1 to O3b observational runs uncovers a rich landscape of anomalies over different timescales, including many that do not fit within known classes.

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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.

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arXiv2025

Holographic $T\bar{T}$ deformation of the entanglement entropy in (A)dS$_3$/CFT$_2$

In recent years, the holographic duality between $T\bar{T}$-deformed conformal field theory (CFT) and Anti-de Sitter (AdS) spacetime with finite radial cutoff has received significant attention. The study of $T\bar{T}$ deformation within the framework of de Sitter (dS)/CFT duality has also progressed. This paper shows that the trace flow equation in dS spacetime can be analytically extended from its AdS counterpart through double Wick rotations. Meanwhile, we generalize the replica method in both AdS and dS holography to derive a general expression for the entanglement entropy of arbitrary single spatial intervals within the $T\bar{T}$-deformed framework. For both finite size and finite temperature systems, we obtain the analytical expression for the entanglement entropy after $T\bar{T}$ deformation. Finally, in dS/dS holography and half-dS holography, we find that the dual field theory exhibits non-locality by analyzing the strong subadditivity and boosted strong subadditivity of entanglement entropy.

hep-th↗

arXiv2025

Polarization modes of gravitational waves in general symmetric teleparallel gravity

In this paper, we investigate the polarization modes of gravitational waves within the most general symmetric teleparallel gravity theory that allows for second-order field equations We consider both scenarios where test particles either carry or do not carry a hypermomentum charge. Our findings reveal the existence of tensor, vector, and scalar modes of gravitational waves. Firstly, the theory supports the + and $\times$ tensor modes propagating at the speed of light. Secondly, in the case where particles do not carry hypermomentum, vector modes propagating at the speed of light exist only within a very specific parameter space. However, when particles do carry hypermomentum, there are two shear modes that propagate at the speed of light, while the vector-$x$ and vector-$y$ modes emerge only under very specific conditions. Thirdly, in the presence of hypermomentum, there is always a longitudinal mode propagating at the speed of light. The universal existence of the shear modes and the longitudinal mode in the presence of hypermomentum is a key feature of symmetric teleparallel gravity, distinguishing it from the Riemannian framework through gravitational wave polarization detection. We also analyze the polarization modes in two widely studied special theories: $f(Q)$ theory and quadratic non-metricity theory. Our study reveals that, within the $f(Q)$ gravity framework, it is crucial to assume that matter fields are independent of the connection, as any dependence would lead to unphysical results.

gr-qc↗

arXiv2025

Gravitational-wave effects in the most general vector-tensor theory

In this paper, we establish a model-independent framework based on the Isaacson picture to analyze the gravitational-wave effects in the most general vector-tensor theory that yields second-order field equations. Within this framework, we derive two basic sets of equations for the Isaacson picture. These equations enable the analysis of gravitational wave polarization modes, the dispersion relation of each mode, the effective energy-momentum tensor of gravitational waves, and the memory effects. These features are closely tied to observable phenomena and have attracted considerable attention. They are expected to be detected by the next generation of gravitational wave observatories designed to test potential modifications to general relativity. Using this framework, we present the explicit expression for the effective energy-momentum tensor of gravitational waves in the most general second-order vector-tensor theory and perform a complete analysis of their polarization modes.

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.

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