arXiv subjects

Zhaoyi Xu

Publications and source records attributed to Zhaoyi Xu.

At least 19 recordsLinked to original sources

arXiv2026

Periodic Orbits of Van der Waals Black Holes

Black holes in asymptotically anti-de Sitter (AdS) spacetime whose extended-phase-space thermodynamics reproduces that of a van der Waals fluid exactly form a distinctive class, the van der Waals black holes (VBHs). The timelike geodesics of VBHs are solved, their periodic orbits are catalogued, and the gravitational waves emitted along them are computed, so as to trace how the thermodynamic pressure P and the molecular-volume parameter b shape the orbital dynamics. Integrating the geodesic equations numerically yields the energy, angular momentum and radius of the innermost stable circular orbit (ISCO) and maps out the family of bound orbits. To delimit the parameter window in which the effective potential stays well behaved, we introduce a critical angular momentum Ls. Within the orbit-classification scheme, we compute the energies corresponding to rational q for several parameter sets and display the resulting orbits. The waveforms produced along these orbits are generated within the "Kludge" formalism, which makes it possible to quantify the imprint of b on the wave amplitude and on the period. Both the orbital architecture and the gravitational-wave signature turn out to be strongly sensitive to b. The dynamical behavior of VBHs and Schwarzschild-AdS (SAdS) black holes differs markedly, providing a new perspective for probing black hole thermodynamics via gravitational wave observations.

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arXiv2026

Multiscale probing of a Hernquist-type environmental black hole spacetime with the Sgr A* shadow and S2 orbital dynamics

The supermassive black hole Sgr A* at the Galactic center provides a unique opportunity to probe the distribution of environmental matter around black holes. In this work, we adopt the Hernquist-type environmental black hole spacetime, a non-vacuum exact solution of the Einstein field equations, as its gravitational model to describe the joint gravitational field of the black hole and its surrounding matter, with environmental effects characterized by the dimensionless compactness $C$ and the characteristic scale $α$. We combine black hole shadow data with two sets of S2 star data provided by Do et al. and Gillessen et al., and constrain the model parameters using the Markov chain Monte Carlo method. At the 95\% credible upper limit, the shadow-only data constrain $C < 1.498\times10^{-1}$.but provide no effective constraint on $α$. The two S2 datasets yield $C<5.239\times10^{-5}$ and $C<1.303\times10^{-4}$, respectively, with $α$ exhibiting a bimodal structure in both cases. After combining the shadow and S2 star data, the $C$ upper limits are tightened to $C<3.760\times10^{-5}$ and $C<1.073\times10^{-4}$, respectively. These results indicate that current observations rule out highly compact configurations of the environmental halo, while the obtained constraints are consistent with the typical compactness range of matter halos. However, $α$ still exhibits a significant bimodal degeneracy, indicating that current observations are insufficient to uniquely determine the radial distribution of the environmental halo. Future observations of multiple stellar orbits may provide further insights into the radial structure of the environmental halo.

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arXiv2026

Quasinormal modes of Kerr-like black bounce spacetime

We investigate the quasinormal mode (QNM) spectrum of a Kerr-like black-bounce spacetime under massive scalar-field perturbations. Starting from the Kerr-like deformation of the Simpson--Visser black-bounce geometry, we derive the corresponding radial and angular equations and obtain the effective potential governing scalar perturbations. The QNM frequencies are computed by means of the Pöschl--Teller potential approximation and the semi-analytic WKB method (up to sixth order), and we demonstrate reasonable agreement between these two approaches. We then analyze in detail how the QNM spectrum depends on the spin parameter $a$, the bounce parameter $p$ that interpolates between black-hole and wormhole geometries, and the scalar-field mass $μ$. Our results show that increasing the spin parameter $a$ raises the oscillation frequency, while increasing the bounce parameter $p$ lowers it, and in both cases the damping rate decreases. Moreover, the mass of the scalar field has a non-negligible impact on the ringdown spectrum. These features suggest that rotating black-bounce geometries may leave distinct imprints in the ringdown phase of gravitational-wave signals, and motivate future studies of echoes and parameter estimation in the context of present and upcoming detectors.

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arXiv2026

Periodic Orbits and Gravitational Wave Radiation of Black Hole in EGB gravity

This paper investigates the orbital dynamics and gravitational wave radiation characteristics of neutral test particles around a static spherically symmetric charged black hole (BH) in 4D Einstein-Gauss-Bonnet (4D-EGB) gravity theory. We analyze the dependence of the marginally bound orbit (MBO) and the innermost stable circular orbit (ISCO) on the Gauss-Bonnet coupling parameter $α$ and charge $Q$. The results indicate that the orbital radius, angular momentum, and energy all decrease with increasing $α$ or $Q$, with the corresponding bound orbit region shifting leftward in the $(E, L)$ parameter space. By combining observational data from the BH shadows of M87* and Sgr A* as well as the orbital precession of the S2 star, we constrain the model parameters and find that existing observations can limit the ranges of $α$ and $Q$ to a certain extent. Furthermore, we investigate the characteristics of periodic orbits corresponding to different rational numbers $q$ and the gravitational waveforms they excite, finding that variations in $α$ and $Q$ can lead to distinguishable differences in periodic orbit structures and gravitational wave phases. This study contributes to understanding the effects of Gauss-Bonnet corrections on BH spacetimes, and the results may provide theoretical references for future gravitational wave observations of extreme mass ratio inspirals (EMRIs).

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arXiv2026

Non-minimally coupled Einstein-Yang-Mills black holes: periodic orbits and gravitational wave radiation in extreme mass ratio systems

Extreme mass ratio inspirals (EMRIs), as a core target for future space-based gravitational wave detection, offer crucial observational grounds for testing strong-field gravitational theories and classifying black holes through their orbital dynamics and gravitational wave radiation characteristics. This study systematically investigates the periodic orbit characteristics and gravitational wave radiation properties of EMRIs in the spacetime of a non-minimally coupled Einstein-Yang-Mills (EYM) black hole. The results show that as the magnetic charge parameter $Q$ and the non-minimal coupling constant $ξ$ increase, the radii of the marginally bound orbit ($r_{\text{MBO}}$) and the innermost stable circular orbit ($r_{\text{ISCO}}$) decrease significantly, with corresponding reductions in the orbital energy $E$ and angular momentum $L$. Furthermore, the allowable parameter space of energy and angular momentum ($E$-$L$) for bound orbits shifts towards the left. We then plot typical periodic orbits through orbit classification, finding that the non-minimal coupling effect suppresses the orbital contraction induced by the magnetic charge, leading to degeneracy of orbits with different $Q$ values towards the Schwarzschild case, as well as phase shifts, amplitude enhancement, and period shortening in the gravitational waveforms with increasing $Q$ and $ξ$. These results provide theoretical predictions for distinguishing different black hole models through future gravitational wave observations.

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arXiv2026

Periodic Orbits and Gravitational Radiation from Extreme Mass-Ratio Inspirals as Probes of Black Hole Quantum Hair

The classical no-hair theorem states that stationary black holes in general relativity can be completely described by only a small set of global parameters. Within this framework, no additional geometric structures are expected to persist outside the event horizon. However, quantum vacuum polarization may introduce small modifications to the near-horizon geometry, effectively giving rise to what is known as quantum hair. Such corrections may provide a possible window into the microscopic structure and thermodynamic properties of black holes. In this work, we examine how the quantum hair parameter γ influences the periodic orbital dynamics of test bodies in extreme mass-ratio inspirals (EMRIs) and their associated gravitational-wave emission. We find that γ significantly modifies the characteristic radii and angular momenta of two important circular orbits, namely the marginally bound orbit (MBO) and the innermost stable circular orbit (ISCO), leading to a shift in the allowed region of the energy-angular momentum (E-L) phase space. Based on the rational number q classification, we further show that quantum corrections tend to enhance the zoom-whirl orbital behavior.Gravitational-wave calculations using the Numerical Kludge approach indicate that quantum hair alters the effective spacetime potential, produces small drifts in the fundamental orbital frequencies, and consequently leads to observable phase dephasing in longduration signals. These results provide a dynamical signature for distinguishing quantum-corrected black holes from classical Schwarzschild ones and offer theoretical motivation for testing quantum gravity effects with future space-based gravitational-wave observatories.

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arXiv2026

Scalar-tensor-vector gravity theory is tested by black hole photon rings

This paper investigates the photon ring and shadow structure of the Reissner-Nordström black hole in the scalar-tensor-vector gravitational framework. The black hole is characterized by the ( MOG) parameter (α) and the charge (Q). The study finds that as (α) increases, the event horizon radius (r_h), photon sphere radius (r_{ph}), and critical impact parameter (b_{ph}) all increase, while these decrease as (Q) increases. The innermost stable circular orbit radius (r_{isco}) exhibits similar monotonic behavior. Ray-tracing shows that as (Q) increases, the impact parameter (b) interval between the lensing ring and photon ring widens; (b_{\text{ph}}) is non-degenerate, and the photon ring radius is uniquely determined by (α) and (Q). Using $EHT$ constraints on (SgrA^*) and (M87^*), the bounds on (α) and (Q) are derived. For (Q = 0), (0.5), and (1), the allowed ranges are (α\in [0, 0.06]), ([0, 0.11]), and ([0.19, 0.36]), respectively. Radiative simulations show that for fixed (Q), larger (α) leads to a larger, non-degenerate photon ring. The Schwarzschild case is approached only when both (α) and (Q) are small. This provides a computational basis for testing modified black holes and offers a non-degenerate observational criterion for distinguishing quantum gravity models, consistent with current $EHT$ data. Future observations with $ngEHT$ and multi-band polarization can further test this. The results suggest that studying the photon ring structure of a Reissner-Nordström black hole in scalar-tensor-vector gravity provides a unique optical diagnostic for potential quantum-gravity tests and black hole properties.

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arXiv2025

Using Randomized Nyström Preconditioners to Accelerate Variational Image Reconstruction

Model-based iterative reconstruction plays a key role in solving inverse problems. However, the associated minimization problems are generally large-scale, nonsmooth, and sometimes even nonconvex, which present challenges in designing efficient iterative solvers. Preconditioning methods can significantly accelerate the convergence of iterative methods. In some applications, computing preconditioners on-the-fly is beneficial. Moreover, forward models in image reconstruction are typically represented as operators, and the corresponding explicit matrices are often unavailable, which brings additional challenges in designing preconditioners. Therefore, for practical use, computing and applying preconditioners should be computationally inexpensive. This paper adapts the randomized Nyström approximation to compute effective preconditioners that accelerate image reconstruction without requiring an explicit matrix for the forward model. We leverage modern GPU computational platforms to compute the preconditioner on-the-fly. Moreover, we propose efficient approaches for applying the preconditioners to problems with classical nonsmooth regularizers, i.e., wavelet, total variation, and Hessian Schatten-norm. Our numerical results on image deblurring, super-resolution with impulsive noise, and 2D computed tomography reconstruction illustrate the efficiency and effectiveness of the proposed preconditioner.

eess.IV↗

arXiv2025

Convergent Complex Quasi-Newton Proximal Methods for Gradient-Driven Denoisers in Compressed Sensing MRI Reconstruction

In compressed sensing (CS) MRI, model-based methods are pivotal to achieving accurate reconstruction. One of the main challenges in model-based methods is finding an effective prior to describe the statistical distribution of the target image. Plug-and-Play (PnP) and REgularization by Denoising (RED) are two general frameworks that use denoisers as the prior. While PnP/RED methods with convolutional neural networks (CNNs) based denoisers outperform classical hand-crafted priors in CS MRI, their convergence theory relies on assumptions that do not hold for practical CNNs. The recently developed gradient-driven denoisers offer a framework that bridges the gap between practical performance and theoretical guarantees. However, the numerical solvers for the associated minimization problem remain slow for CS MRI reconstruction. This paper proposes a complex quasi-Newton proximal method that achieves faster convergence than existing approaches. To address the complex domain in CS MRI, we propose a modified Hessian estimation method that guarantees Hermitian positive definiteness. Furthermore, we provide a rigorous convergence analysis of the proposed method for nonconvex settings. Numerical experiments on both Cartesian and non-Cartesian sampling trajectories demonstrate the effectiveness and efficiency of our approach.

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arXiv2025

Shadows and Observational Images of a Schwarzschild-like Black Hole Surrounded by a Dehnen-type Dark Matter Halo

This paper investigates the optical appearance of a Schwarzschild-like black hole (BH) surrounded by a Dehnen-(1, 4, 5/2) type dark matter (DM) halo, with a focus on how the DM halo's density $ρ_{s}$ and radius $r_{s}$ influence the BH's shadow and photon ring. First, the radius $r_h$ of the BH's event horizon and the equation of motion for photons were derived, and observational data from the Event Horizon Telescope (EHT) for M87* were used to constrain the parameters $ρ_{s}$ and $r_{s}$ of the DM halo. Afterward, by varying the values of $ρ_{s}$ and $r_{s}$, key parameters such as the effective potential $V_{eff}$ of photons, the critical impact parameter $b_{ph}$, the radius $r_{isco}$ of the innermost stable circular orbit, and the radius $r_{ph}$ of the photon sphere were calculated for each case. It was found that as $ρ_{s}$ and $r_{s}$ increase, the above mentioned parameters all show an increasing trend. Subsequently, we investigated the optical appearance of the BH illuminated by two types of accretion models: optically and geometrically thin disk models and spherical accretion models. The findings indicate that as $ρ_{s}$ and $r_{s}$ increase, the peak of the received intensity shifts toward a higher impact parameter $b$, resulting in a distinct optical appearance.

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arXiv2025

Constraints on the Scale Parameter of Regular Black Hole in Asymptotically Safe Gravity from Extreme Mass Ratio Inspirals

This paper evaluates the potential for constraining the quantum scale parameter $ξ$ of regular black hole within the asymptotically safe gravity framework using gravitational waves from extreme mass ratio inspirals (EMRIs). Since $ξ$ cannot be precisely determined from first principles, observational constraints become crucial. We employ the Augmented Analytical Kludge (AAK) method to calculate gravitational waveforms in the equatorial plane and systematically analyze the influence of different $ξ$ values on phase evolution. Comparison with the Schwarzschild case demonstrates that the corrective effects of $ξ$ accumulate in the phase over observation time, thereby providing distinguishable observational signatures. Through waveform mismatch analysis, our results indicate that the LISA detector can effectively detect the presence of $ξ$ at the $\sim10^{-4}$ level for systems with a mass of $10^6M_\odot$. Further assessment using the Fisher information matrix (FIM) confirms a measurement precision of $Δξ\approx3.225\times10^{-4}$, which significantly surpasses existing observational methods, providing quantitative observational evidence for asymptotically safe quantum gravity theory in the strong-field regime.

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arXiv2025

Shadow constraints of charged black hole with scalar hair and gravitational waves from extreme mass ratio inspirals

Black hole (BH) shadow observations and gravitational wave astronomy have become crucial approaches for exploring BH physics and testing gravitational theories in extreme environments. This paper investigates the charged black hole with scalar hair (CBH-SH) derived from the Einstein-Maxwell-conformal coupled scalar (EMCS) theory. We first constrain the parameter space $(Q/M, s/M^2)$ of the BH using the Event Horizon Telescope (EHT) observations of M87* and Sgr A*. The results show that M87* provides stronger constraints on positive scalar hair, constraining the scalar hair $s$ within $0\le s/M^2\le0.4632$ and the charge $Q$ within the range $0\le Q/M\le0.6806$. In contrast, Sgr A* imposes tighter constraints on negative scalar hair. When $Q$ approaches zero, $s$ is constrained within the range $0\geq s/M^2\geq-0.0277$. Overall, EHT observations can provide constraints at most on the order of $\mathcal{O}\left({10}^{-1}\right)$. Subsequently, we construct extreme mass ratio inspiral (EMRI) systems and calculate their gravitational waves to assess the detection capability of the LISA detector for these BHs. The results indicate that for central BHs of $M={10}^6M_\odot$, LISA is expected to detect scalar hair $s/M^2$ at the $\mathcal{O}\left({10}^{-4}\right)$ level and charge $Q/M$ at the $\mathcal{O}\left({10}^{-2}\right)$ level, with detection sensitivity far exceeding the current EHT capabilities. This demonstrates the immense potential of EMRI gravitational wave observations in testing EMCS theory.

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arXiv2025

Testing Extended Theories of Gravity via Black Hole Photon Rings

This research delves into the optical characteristics of stationary, spherically symmetric black holes. These black holes follow the Konoplya-Zhidenko deformation rule in arbitrary gravity theories. This research finds that the effects of $a_2$ and $b_2$ on photon orbital dynamics exhibit observational degeneracy, while $\varepsilon$ significantly governs photon capture characteristics. As $\varepsilon$ increases, the radius of the photon sphere $r_{\text{ph}}$ and the critical impact parameter $b_{\text{ph}}$, and the innermost stable circular orbit radius $r_{\text{isco}}$ all increase. The event horizon $ r_{\text{h}} $ corresponds to that of the Schwarzschild black hole, while the impact parameter range for the lens and photon rings is reduced. Black hole shadow and photon ring analyses across three emission models show that increasing $\varepsilon$ shifts the peak rightward while enlarging the photon ring radius. The closer $\varepsilon$ is to zero, the more the results approach the Schwarzschild case, the more the results approach the Schwarzschild case. Additionally, by combining EHT observational data on the shadow diameters of M87 and Sgr A*, we imposed constraints on the correlation parameter $\varepsilon$ in the theoretical model(at the confidence level anchored by $d_{\text{sh}}^{(M87^*)}$, the parameter $\varepsilon$ is confined to the interval $-0.09 \lesssim \varepsilon \lesssim 0.19$. For $d_{\text{sh}}^{(Sgr A^*)}$, the constraint on $\varepsilon$ is delineated as $-0.280 \lesssim \varepsilon \lesssim 0.047$). The results show that within the observationally allowed range of $\varepsilon$ (such as $[-0.04, 0.04]$), the characteristics of the black hole exhibit specific regularities with changes in $\varepsilon$.

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arXiv2025

Strong Gravitational Lensing Effects of the Rotating Short-Haired Black Hole and Constraints from EHT Observations

For the short hairs that have a significant impact only near the event horizon, studying their strong gravitational lensing effects is of great significance for revealing the properties of these hairs. In this study, we systematically investigated the strong gravitational lensing effects in the rotating short-haired black hole and constrained its hair parameter $Q_m$. Specifically, $Q_m$ causes the event horizon radius, photon - orbit radius, and impact parameter to be lower than those of the Kerr black hole. Regarding the lensing coefficients $\bar{a}$ and $\bar{b}$, as the spin parameter $a$ increases, $\bar{a}$ shows an increasing trend, while $\bar{b}$ shows a decreasing trend. In the observational simulations of M87* and Sgr A*, the angular position and angular separation of the relativistic image increase with the increase of $a$, while the magnification of the image shows an opposite trend. The existence of $Q_m$ only intensifies these trends, while parameter $k$ suppresses such tendencies. More importantly, the rotating short-haired black hole exhibits a significant difference in time delay compared to other black hole models. Especially in the simulation of M87*, the time delay deviation between the rotating short-haired black hole and the Kerr black hole, as well as the Kerr-Newman black hole, can reach dozens of hours. Through a comparative analysis with the observational data from the EHT, we effectively constrain the parameter space of the rotating short-haired black hole. The results indicate that this model has potential application prospects in explaining cosmic black hole phenomena and provides a possible theoretical basis for differentiating between different black hole models.

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arXiv2025

Bound Orbits and Gravitational Wave Radiation Around the Hairy Black Hole

The hairy black hole model provides a new theoretical framework for exploring phenomena in strong gravitational fields. This paper systematically investigates the influence of the hair parameter $β$ on the timelike geodesics of the regular hairy black hole, including the radius of the event horizon, the properties of bound orbits, and the characteristics of gravitational wave radiation over a single period. The study reveals that $β$ has a significant impact on the event horizon but only a minor effect on the innermost stable circular orbit(ISCO), the marginally bound orbit(MBO), and periodic orbits. Moreover, the trajectories of the periodic orbits are nearly identical to those of the Schwarzschild black hole. In addition, the parameter $β$ was constrained by simulating the precession observational data of the S2 star orbiting the supermassive black hole Sgr A*. The results indicate that the correction effects of $β$ comply with existing observational constraints, without providing stricter limitations. Furthermore, by considering periodic orbits as transitional orbits in the extreme-mass-ratio inspiral (EMRI) system, it is found that the presence of $β$ introduces subtle effects on the amplitude, phase, and period of the gravitational wave signal for a single orbit. Although these effects appear minor within a single cycle, they may accumulate into significant effects over long-term evolution. In the future, space-based gravitational wave detectors are expected to further investigate the properties of the hair parameter, enhancing our understanding of the spacetime structure and dynamical behavior of black holes.

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arXiv2025

Distinguishing Between Dark Matter-Black Hole Systems and Naked Singularities via Quasi-Periodic Oscillations

Quasi-Periodic Oscillations (QPOs) are an important phenomenon commonly observed in the X-ray radiation of black holes and neutron stars, closely related to the dynamics of accretion disks around compact objects and general relativistic effects. The objective of this study is to use the QPO phenomenon to distinguish between dark matter-black hole systems and naked singularities, as well as to investigate the effects of different dark matter models (Cold Dark Matter, CDM, and Scalar Field Dark Matter, SFDM) on the accretion disk dynamics. By introducing a dark matter correction model within the framework of general relativity, we systematically investigate the differences in dragging effects, characteristic frequency distribution, and the innermost stable circular orbit (ISCO) radius between dark matter-black hole systems and naked singularities, while analyzing the potential coupling between QPO frequencies and dark matter distribution. The main results of this study are as follows: $ν_r$ and $ν_θ$ in dark matter-black hole systems can be identified as HFQPOs, while for lower spins ($a < 0.5$), $ν_\text{nod}$ can be identified as LFQPOs, and for higher spins ($1 > a \geq 0.5$), $ν_\text{nod}$ falls within the HFQPO observation range. Cold Dark Matter (CDM) and Scalar Field Dark Matter (SFDM) modulate the accretion disk dynamics at the order of $10^{-6}$.

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arXiv2025

Periodic orbits and gravitational wave radiation in short hair black hole spacetimes for an extreme mass ratio system

For a short hair black hole(BH) which circumvents the "no-short-hair" theorem, it manifests intense hair behavior in the vicinity of the event horizon, accompanied by remarkable quantum effects. These effects may carry important information about the internal structure and dynamical evolution of BHs, thereby providing a new perspective on the problem of black hole information loss. Therefore, in this paper, we analyze the influence of the hair parameter $Q_m$ and the structural parameter $k$ of the short hair BH in an extreme mass ratio(EMR) system on the periodic orbits of particles and gravitational wave radiation. The results show that as $Q_m$ increases, the radius and angular momentum of the bound orbit decrease, and the $E-L$ space shifts to the left. An increase in $k$ weakens this trend. When $k$ takes a larger value, the short hair BH and the Schwarzschild BH tend to be degenerate. Compared with the Schwarzschild BH, the bound orbit energy and angular momentum of the short hair black hole are reduced. Under the conditions of higher $Q_m$ and lower $k$, the gravitational wave period is suppressed and the signal amplitude is significantly increased. These results provide new observational means for distinguishing short hair BH from classical BH and offer new insights for verifying the no-hair theorem and understanding the physical behavior near the event horizon.

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arXiv2025

Testing Einstein Maxwell Power-Yang-Mills Hair via Black Hole Photon Rings

In this paper, the optical appearance of static and spherically symmetric hairy black holes is studied under the standard Einstein-Maxwell theory considering the p-power Yang-Mills term. During the research process, the specific case of $p=1/2$ was mainly selected for discussion. To understand the impact of the hairy parameter on black holes, we have studied the event horizon radius $r_{h} $, the photon sphere radius $r_{ph}$ and the radius of the innermost stable circular orbit $r_{isco}$ of this hairy black hole. Then, we utilized the backward ray-tracing method to analyze the geodesics of photons around this black hole and discussed the influence of the hairy parameter on the photon geodesics. In addition, we also calculated the unique shadow and photon ring of the black hole irradiated by a static thin accretion disk with three toy model emission functions. The research results show that as the hairy parameter gradually increases, the event horizon radius $r_{h} $, the photon sphere radius $r_{ph}$, the radius of the innermost stable circular orbit $r_{isco}$ and the critical impact parameter $b_{ph}$ of the black hole all exhibit a decreasing trend. Meanwhile, it also causes the area of the black hole shadow and the photon ring to decrease accordingly. Consequently, in the case of the static and spherically symmetric standard Einstein Maxwell power-Yang-Mills hairy black hole, there is no degeneracy in the photon ring and the shadow. Theoretically, it can reflect different black hole solutions and thus verify the Yang-Mills hair.

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