arXiv subjects

Yu-Peng Zhang

Publications and source records attributed to Yu-Peng Zhang.

At least 19 recordsLinked to original sources

arXiv2026

Spectral Butterfly Effect and Resilient Ringdown in Thick Braneworlds

The quasinormal mode spectrum is a unique fingerprint linking gravitational-wave observations to extra-dimensional geometry. In this Letter, we show that thick braneworlds exhibit a spectral butterfly effect: infinitesimal deformations of the effective potential trigger dramatic migrations of quasinormal modes, challenging the presumed stability of this fingerprint. Frequency-domain instabilities depend sensitively on the perturbation's location and strength. In the time domain, near-brane perturbations primarily modify the early ringdown, while far-brane perturbations generate clean late-time echoes. Crucially, the graviton zero mode remains localized, preserving four-dimensional gravity. Despite this pronounced spectral fragility, the observable early-stage signal under current detector sensitivities is still dominated by the original fundamental mode. Hence, thick braneworlds display a nontrivial coexistence of a fragile spectrum and a resilient ringdown, supporting the continued use of the standard fingerprint in present-day gravitational-wave astronomy while revealing its hidden sensitivity.

gr-qc↗

arXiv2026

Violation of cosmic censorship in Einstein-Maxwell-Scalar models with fractional coupling

The weak cosmic censorship conjecture plays a foundational role in classical gravity by asserting that spacetime singularities are generically hidden behind event horizons. In this work, we explore its robustness in the Einstein-Maxwell-Scalar theory with fractional coupling by studying both static black hole solutions and their fully nonlinear dynamical evolution. We identify a class of scalarized black holes that develop negative energy density near the event horizon, indicating violations of the classical energy conditions. Numerical evolutions of perturbed configurations reveal that sufficiently strong fractional coupling drives rapid curvature growth and geometric degeneration in the near-horizon region, accompanied by persistent negative energy density. While the simulations do not resolve the ultimate end state, the observed dynamics consistently point toward a weakening of the horizon-supporting structure and are suggestive of incipient naked singularity formation. These results uncover a classical mechanism through which fractional coupling can challenge the validity of the weak cosmic censorship conjecture in asymptotically flat spacetimes.

gr-qc↗

arXiv2026

Self-resonance preheating in deformed attractor models: oscillon formation and evolution

It is well known that, in potentials that are quadratic near the minimum but shallower away, such as small $\alpha$ ($\ll M_P^2$) attractors, the inflaton condensate fragments into localized compact objects known as oscillons during self-resonance preheating. In this work we investigate the self-resonance in deformed $\alpha$-attractor T-model with a Gaussian feature near the minimum, distant from inflation's end. Linear analysis reveals altered resonance bands and deformed Floquet charts dependent on feature parameters. In fully nonlinear lattice simulations, we find that the gradient energy transfer is largely independent of the potential feature parameter $h$. In contrast, after resonance terminates, the subsequent evolution of gradient energy becomes strongly dependent on $h$. Statistical analysis reveals that models with the potential feature produce larger number of smaller oscillons, with a reduced energy stored in these objects, increasingly suppressed as the magnitude of $h$ grows. By tracking the total energy and the gradient energy contained in oscillons, we find that in models with nonzero $h$ oscillons are systematically shorter-lived, with this effect strengthening for larger $h$. The gravitational wave emission is dominated by the resonance stage and is strongly suppressed once oscillons form. Potential features leave the low-frequency spectrum largely unchanged but significantly modify the high-frequency tail. Although a complete reheating description requires external couplings and higher-resolution simulations, clear qualitative differences of cosmic expansion history already emerge within our simulated time window. These results highlight the important role of potential features in shaping reheating dynamics and their cosmological implications, and provide a deeper understanding of preheating dynamics and the properties of oscillons.

astro-ph.CO↗

arXiv2026

Effects of nonlinear interactions on the superradiant instability of charged black holes

A Reissner-Nordstr\"{o}m black hole (RNBH) enclosed in a cavity is known to be superradiantly unstable to charged scalar perturbations below a critical frequency. Inspired by the emergence of the QCD axion as a prominent dark matter candidate, we construct a model featuring an axion field coupled to an electromagnetic field that undergoes superradiant growth around an RNBH. Utilizing numerical relativity, we achieve stable, long-term evolution of this system and perform a comparative analysis across various parameter spaces. Our comprehensive investigation reveals the formation of a hairy black hole, whose final state is governed by a diverse set of physical parameters. Notably, the decay constant in the axion potential, representing nonlinear interactions, bifurcates the superradiant instability into two distinct behavioral regimes, leading to more significant dynamical shifts than previously reported. Furthermore, we examine the influence of the scalar field's charge and mass, as well as the mirror's position. We investigate the axionic bosenova process and observe a long-term beating pattern of the axion field induced by nonlinear interactions. By fine-tuning these parameter combinations, we demonstrate that the system can evolve toward a variety of distinct physical endpoints.

gr-qc↗

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. 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.

gr-qc↗

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 $\hat{\alpha}$ 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 $\hat{\alpha}$, we show that even small corrections $(\hat{\alpha} \sim 10^{-5})$ 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.

gr-qc↗

arXiv2025

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 $\alpha_1$, 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.

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: $\alpha=1$, $\beta=2$, and $\gamma=d-3$, 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

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

Orbits of photon in Bardeen-boson stars and their frozen states

In a recent study [1], the Bardeen-boson star (BBS) model involving a scalar field minimally coupled to Einstein gravity and a Bardeen's nonlinear electromagnetic field was investigated. It was found that when the magnetic charge $q$ of the electromagnetic field exceeds a certain critical value $q_c$, a frozen Bardeen-boson star (FBBS) can be obtained with the frequency approaching zero. In this paper, we study the null orbits in the background of the general BBS and FBBS. We find that similar to the boson star (BS), all BBSs do not have the event horizon and possess complete null geodesics, allowing photons to move throughout the entire spacetime of BBS. Among these BBSs, the FBBSs whose spacetime is very similar to that of black holes are particularly special. The null orbits around the FBBSs exhibit sharp deflections near the critical horizon while becoming nearly straight inside the critical horizon. Furthermore, the photon in the background of FBBSs moves for a very long time inside the critical horizon from the perspective of an infinity viewer.

gr-qc↗

arXiv2025

Emerging black hole shadow from collapsing boson star

This work devotes to investigate the dynamical emergence of black hole shadow from gravitational lensing in dynamical spacetime by using the collapsing boson star. Two characterized scenarios are adopted with or without considering the time delay of light propagation. As the boson star evolves, new Einstein rings emerge from the lensing center, with their radius gradually increasing, and their number continues to grow infinitely before the light-ring forms. The shadow forms instantaneously at the moment the black hole appears when ignoring the time delay of light propagation. Considering the time delay for light propagation in dynamical spacetime, a more intricate process of the shadow formation is uncovered: it first appears as a minute dot in the lensing center, then gradually grows as the black hole grows, eventually expands the inner region of the light-ring. During the quasi-stable phases of boson star and black hole, the lensing and shadow structures from two scenarios are nearly identical and remain almost unchanged. Our results present the universal dynamic patterns of the lensing and shadow structures, and reveal the potential observed phenomena near the collapsing star and the event horizon of the newly formed black hole.

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↗

arXiv2024

Dynamical formation of axionic hair around charged black hole

In this paper, we present a nonlinear numerical investigation on the dynamical scalarization process of a Reissner-Nordstr\"om black hole, incorporating an axionic scalar potential within the framework of the Einstein-Maxwell-dilaton theory. By scrutinizing the evolution of the irreducible mass of the black hole and the value of scalar field on the apparent horizon across various parameters of the axionic potential, we elucidate the correlations between the final states of scalarized charged black hole and the axionic potential. We observe that the inclusion of the axionic potential can either decrease or increase the irreducible mass of the final scalarized black hole, depending on the strength of the coupling between the dilation and the electric invariant $F_{\mu\nu}F^{\mu\nu}$. Regarding the value of the scalar field on the apparent horizon, we find that it decreases with the inclusion of the axionic potential. Our results contribute to an important understanding of the dynamical scalarization of black holes and the potential configurations of scalar hair with various self-interactions.

gr-qc↗

arXiv2024

Constraining polymerized black holes with quasi-circular extreme mass-ratio inspirals

In this paper, we focus on the gravitational waves emitted by a stellar-mass object in a quasi-circular inspiral orbit around a central supermassive polymerized black hole in loop quantum gravity. Treating the stellar-mass object as a massive test particle, we derive its equations of motion and the corresponding radial effective potential. We find that the peak of the radial effective potential decreases with the quantum parameter $\hat{k}$. We also examine the impact of quantum corrections on the properties of stable circular orbits around the polymerized black hole. We model the smaller object's trajectory as an adiabatic evolution along stable circular orbits using a semi-relativistic approach. In this method, the motion of the object is described by relativistic geodesics, and changes in the object's energy and orbital angular momentum due to gravitational radiation are calculated using the mass quadrupole formula. The corresponding gravitational waveforms are generated using the numerical kludge method, revealing that quantum corrections cause phase advances in the gravitational waveforms. We further analyze the potential constraints on the quantum parameter $\hat{k}$ from future space-based gravitational wave observations, concluding that these observations will likely impose stronger constraints on $\hat{k}$ than those obtained from black hole shadow measurements.

gr-qc↗

arXiv2024

Gravitational waveforms from periodic orbits around a quantum-corrected black hole

Extreme mass-ratio inspirals are crucial sources for future space-based gravitational wave detections. Gravitational waveforms emitted by extreme mass-ratio inspirals are closely related to the orbital dynamics of small celestial objects, which vary with the underlying spacetime geometry. Despite the tremendous success of general relativity, there are unsolved issues such as singularities in both black holes and cosmology. Loop quantum gravity, a theory addressing these singularity problems, offers a framework for regular black holes. In this paper, we focus on periodic orbits of a small celestial object around a supermassive quantum-corrected black hole in loop quantum gravity and compute the corresponding gravitational waveforms. We view the small celestial object as a massive test particle and obtain its four-velocity and effective potential. We explore the effects of quantum corrections on marginally bound orbits, innermost stable circular orbits, and other periodic orbits. Using the numerical kludge scheme, we further explore the gravitational waveforms of the small celestial object along different periodic orbits. The waveforms exhibit distinct zoom and whirl phases in a complete orbital period, closely tied to the quantum parameter $\hat \alpha$. We also perform a spectral analysis of the gravitational waves from these periodic orbits and assess their detectability. With the steady progress of space-based gravitational wave detection programs, our findings will contribute to utilizing extreme mass-ratio inspirals to test and understand the properties of quantum-corrected black holes.

gr-qc↗

arXiv2024

Role of Coulomb interaction in elastic pion-proton scattering from holography

Differential cross sections of the elastic pion-proton scattering are investigated at very small momentum transfer in a holographic QCD model, considering both the strong and Coulomb interaction in the Regge regime. The strong interaction is described by the Pomeron and Reggeon exchange, and the Coulomb interaction is characterized by the one photon exchange. The two interactions are linked through an interference term and we only need to determine a single adjustable parameter involved in this term. As to the parameters for the strong interaction, we can utilize the values determined in the previous studies. The differential cross sections can be predicted without any additional parameters, and it is shown that our predictions are consistent with the experimental data. We explicitly show the momentum transfer dependence for the interference effect. The energy dependence of the contribution ratios for each component is also discussed.

hep-ph↗

arXiv2024

Multi-kink brane in Gauss-Bonnet gravity and its stability

Einstein-Gauss-Bonnet gravity in high dimensional spacetime is intriguing. Here, the properties of thick branes generated by a bulk scalar field in the five-dimensional Einstein-Gauss-Bonnet gravity were studied. With the help of the superpotential method, we obtain a series of multi-kink brane solutions. We also analyze the linear stability of the brane system under tensor perturbations and prove that they are stable. The massless graviton is shown to be localized near the brane and hence the four-dimensional Newtonian potential can be recovered. By comparing the properties of these thick branes under different superpotentials we find with some specific choice of superpotential the Gauss-Bonnet term can determine the scalar field are multi-kink or single kink.

hep-th↗

arXiv2024

Characteristic modes of thick brane model: resonances and quasinormal modes

In this work, we investigate the gravitational quasinormal modes (QNMs) and the gravitational resonances of a thick brane model. We use the asymptotic iteration and shooting methods to obtain the quasinormal frequencies (QNFs) of the brane. On the other hand, we investigate the resonances and their evolution numerically. The results show that the oscillations of the resonances equal (up to numerical error) to the real parts of the QNFs, while the damping rates of the resonances equal to the imaginary parts of the QNFs. The QNMs and resonances, both of them can be regarded as the characteristic modes of the thick brane, are closely related with each other. In addition, the lifetime of these QNMs could be very long, perhaps they might be detected in future accelerator or gravitational wave detector.

gr-qc↗