arXiv subjects

Zhaoyi Xu

Publications and source records attributed to Zhaoyi Xu.

At least 37 records · Page 2Linked to original sources

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.

gr-qc↗

arXiv2025

Yang-Mills field modified RN black hole and the Strong Cosmic Censorship Conjecture

To address the singularity problem in black hole physics, Penrose proposed the cosmic censorship conjecture . However, whether this conjecture holds in different types of black holes, especially for the Strong Cosmic Censorship Conjecture (SCCC), remains an issue worth further exploration. This study investigates the Yang-Mills field modified RN black hole, which provides new possibilities for exploring the Strong Cosmic Censorship Conjecture due to its unique nonlinear dynamical properties. In this work, the perturbation equations of two scalar fields for the Yang-Mills field modified RN black hole are derived. By combining the WKB method and the Prony method, the quasi-normal modes frequencies of the perturbations are analyzed. Additionally, constraints on the charge-to-mass ratio of the charged and massive scalar field are obtained using the Weak Gravity Conjecture (WGC), and it is shown that the Yang-Mills field modified RN black hole satisfies the SCCC conditions in the extreme state. The study reveals that the Yang-Mills field charge $q_{YM}$ significantly affects the damping effect and gravitational blueshift effect of the perturbations, causing the RN black hole in the extreme state to transition from violating the SCCC to satisfying it. Furthermore, when the charge-to-mass ratio $q/m$ of the charged and massive scalar field satisfies the WGC condition, the scalar field perturbations destabilize the Cauchy horizon of the Yang-Mills field modified RN black hole in the extreme state, thus confirming the applicability of the SCCC under extreme conditions. This study highlights the key role of nonlinear fields in singularity theory and gravitational dynamics, providing important support for the completeness of general relativity and offering new insights into the theoretical research of black holes in extreme states.

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arXiv2024

Test the weak cosmic censorship conjecture via black hole in dark matter halo

The weak cosmic censorship conjecture states that the black hole singularity is hidden inside the event horizon of the black hole, making it impossible for an external observer to measure. In this study, we investigate the weak cosmic censorship conjecture test of dark matter halo-black hole systems in both the cold dark matter model and ultralight dark matter model scenarios, with the aim of gaining insights into the influence of dark matter particles on the weak cosmic censorship conjecture. By examining the particle incident on an extremely or nearly extremal dark matter - black hole, as well as the scattering of a scalar field by an extreme or near-extreme dark matter - black hole. We find that, for test particles, the weak cosmic censorship conjecture is violated under extreme conditions. Under near-extreme conditions, our calculation results show a second-order small quantity, which indicates that the weak cosmic censorship conjecture may be breached under near-extreme conditions. However, if the self-force effect is taken into consideration, whether the weak cosmic censorship conjecture will be violated still requires further in-depth research. For scalar fields, the weak cosmic censorship conjecture is violated under extreme conditions, while under near-extreme conditions, our results show that the weak cosmic censorship conjecture still holds. This research will contribute to furthering our comprehension of the intricate interplay between dark matter and black holes.

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arXiv2024

The Lensing Effect of Quantum-Corrected Black Hole and Parameter Constraints from EHT Observations

The quantum-corrected black hole model demonstrates significant potential in the study of gravitational lensing effects. By incorporating quantum effects, this model addresses the singularity problem in classical black holes. In this paper, we investigate the impact of the quantum correction parameter on the lensing effect based on the quantum corrected black hole model. Using the black holes $M87^*$ and $Sgr A^*$ as our subjects, we explore the influence of the quantum correction parameter on angular position, Einstein ring, and time delay. Additionally, we use data from the Event Horizon Telescope observations of black hole shadows to constrain the quantum correction parameter. Our results indicate that the quantum correction parameter significantly affects the lensing coefficients $\bar{a}$ and $\bar{b}$, as well as the Einstein ring. The position $θ_{\infty}$ and brightness ratio $S$ of the relativistic image exhibit significant changes,with deviations on the order of magnitude of $\sim 1μas$ and $\sim 0.01μas$, respectively. The impact of the quantum correction parameter on the time delay $ΔT_{21}$ is particularly significant in the $M87^*$ black hole, with deviations reaching up to several tens of hours. Using observational data from the Event Horizon Telescope(EHT) of black hole shadows to constrain the quantum correction parameter, the constraint range under the $M87^*$ black hole is $0\le \fracα{M^2}\le 1.4087$ and the constraint range under the $Sgr A^*$ black hole is $0.9713\le \fracα{M^2}\le 1.6715$ . Although the current resolution of the EHT limits the observation of subtle differences, future high-resolution telescopes are expected to further distinguish between the quantum-corrected black hole and the Schwarzschild black hole, providing new avenues for exploring quantum gravitational effects.

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arXiv2024

Destroying the Event Horizon of Cold Dark Matter-Black Hole System

Since the Weak Cosmic Censorship Conjecture was proposed, research on this conjecture has been ongoing. This paper explores the conjecture in black holes that are closer to those existing in the real universe (i.e., rotating black holes enveloped by dark matter). In this paper, we obtained a first-order corrected analytical solution for the black hole event horizon through an approximate solution. The validity of the first-order corrected analytical solution will be provided in the appendix. We conduct our study by introducing a test particle and a scalar field into the black hole. Our conclusions show that, in extremal case, both a test particle and a scalar field can disrupt the event horizon of the Kerr-like black hole; in near-extremal case, both a test particle and a scalar field can disrupt the event horizon of the Kerr-like black hole. When cold dark matter is not considered, the conclusion is consistent with previous research.

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arXiv2024

Short-Hair Black Holes and the Strong Cosmic Censorship Conjecture

The singularity problem has always been a focus of physicists' research. In order to solve this problem, Penrose proposed the cosmic censorship conjecture, but verifying this conjecture in different situations still faces many challenges. In the context of short-hair black hole research, this paper explores whether the Strong Cosmic Censorship Conjecture (SCCC) is obeyed by the universe when it is disturbed by a scalar field. In this paper, we explore whether the short-hair black hole satisfies the SCCC under scalar field perturbations. Using the Weak Gravity Conjecture (WGC) and the WKB approximation method within the framework of general relativity, we systematically analyze the behavior of short-hair black holes under different parameter conditions. The focus is on whether violations of the SCCC occur when the black hole approaches extremal conditions. The results show that when the charge Q of the short-hair black hole approaches its extremal value, the SCCC is violated. However, as the order k of the black hole's metric equation and the angular momentum quantum number l increase, the phenomenon of SCCC violation is delayed. These findings indicate that the proximity of the black hole's charge Q to extremality, as well as the values of the angular momentum quantum number l and the order k, play crucial roles in exploring black hole physics and verifying the SCCC. This research not only reveals the behavior of short-hair black holes under extreme conditions but also provides a new perspective for further investigation of the SCCC.

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arXiv2024

Exploring the Possibility of Testing the No-Hair Theorem with Minkowski-deformed Regular Hairy Black Holes Via Photon Rings

In this paper, we investigate the optical appearance of a regular static spherically symmetric hairy black hole within the context of Minkowski deformation governed by the parameter $α$. This black hole describes a hairy black hole with geometric deformations in the radial and temporal metric components, parameterized by $α$. The optical appearance of the black hole, illuminated by a static thin accretion disk in three toy emission function models, exhibits distinctive shadows and photon rings. Our findings reveal that for static spherically symmetric hairy Minkowski-deformed regular black holes, the event horizon radius $r_h$, photon sphere radius $r_{ph}$, critical impact parameter $b_{ph}$, and innermost stable circular orbit radius $r_{isco}$ all have a positive correlation with $α$. These parameters affect the null geodesic trajectories, shadows, and the optical appearance of the photon rings illuminated by a static thin accretion disk around the black hole. Utilizing this, we obtained the optical appearance of this black hole when observed in the forward direction of the optical and geometric thin accretion disk models. In all three models, the radius of the photon ring images also shows a positive correlation with the parameter $α$. Therefore, under the static spherically symmetric hairy Minkowski-deformed regular black hole, there is no degeneracy of photon rings dependent on the parameter $α$. Theoretically, this allows for the distinction of different spacetime metrics of hairy Minkowski-deformed regular black holes, providing a potential method for testing the no-hair theorem through future observations of black hole photon rings.

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arXiv2024

Sensor Selection via GFlowNets: A Deep Generative Modeling Framework to Navigate Combinatorial Complexity

The performance of sensor arrays in sensing and wireless communications improves with more elements, but this comes at the cost of increased energy consumption and hardware expense. This work addresses the challenge of selecting $k$ sensor elements from a set of $m$ to optimize a generic Quality-of-Service metric. Evaluating all $\binom{m}{k}$ possible sensor subsets is impractical, leading to prior solutions using convex relaxations, greedy algorithms, and supervised learning approaches. The current paper proposes a new framework that employs deep generative modeling, treating sensor selection as a deterministic Markov Decision Process where sensor subsets of size $k$ arise as terminal states. Generative Flow Networks (GFlowNets) are employed to model an action distribution conditioned on the state. Sampling actions from the aforementioned distribution ensures that the probability of arriving at a terminal state is proportional to the performance of the corresponding subset. Applied to a standard sensor selection scenario, the developed approach outperforms popular methods which are based on convex optimization and greedy algorithms. Finally, a multiobjective formulation of the proposed approach is adopted and applied on the sparse antenna array design for Integrated Sensing and Communication (ISAC) systems. The multiobjective variation is shown to perform well in managing the trade-off between radar and communication performance.

cs.LG↗

arXiv2024

The Weak Cosmic Censorship Conjecture in Hairy Kerr Black Holes

The Weak Cosmic Censorship Conjecture, since its proposal, has always been a controversial hypothesis, but its significance in astrophysics is undeniable. For a regular black hole, its center does not contain a singularity, and the destruction of the horizon of such black holes is not protected by the Weak Cosmic Censorship Conjecture. Therefore, we employ Gedanken experiments to study the hairy Kerr black holes, which are promising candidates to serve as "simulators" of astrophysical black holes. By investigating these black holes through testing particles and scalar fields carrying large angular momentum, we explore whether these black holes can achieve overspinning. Our results suggest that the overspinning behavior of these hairy Kerr black holes in extremal or near-extremal conditions strongly depends on the hairy parameters (${α, l_0}$). This not only potentially offers us an opportunity to explore the interior structure of black holes, but may also provide clues for constraining the hairy parameters. This phenomenon might reveal the connection between the no-hair theorem of black holes and the weak cosmic censorship conjecture, bringing new perspectives to our understanding of these theories.

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arXiv2024

Testing The Weak Cosmic Censorship Conjecture in Short Haired Black Holes

The Weak Cosmic Censorship Conjecture is a hypothesis regarding the properties of event horizons and singularities during the formation of black holes, stating that singularities are always encompassed by the event horizons(TEH) of black holes, thus preventing naked singularities from affecting the causal structure of spacetime. In this paper, we explore the Weak Cosmic Censorship Conjecture in the context of rotating hairy black holes, aiming to understand the impact of hairiness on the conjecture for Kerr black holes. We investigate whether TEH of rotating hairy black holes can be disrupted by incoming test particles and scalar fields. When test particles and scalar fields incident on the rotating hairy black hole are found. In extreme cases, when considering a second order approximation, if the parameter $κ$ (The parameter here is a function related to hair strength $κ(Q_m^{2k})$.)falls within the range of $0<κ<\sqrt{1/3}$, TEH of a hairy black hole can be disrupted. Conversely, in the range of $\sqrt{1/3}<κ<1$, TEH of a hairy black hole cannot be disrupted. When considering the second order approximation in near extreme cases, the parameter $κ$, within the range of $0<κ<1$, can lead to the disruption of TEH in this spacetime. When an incident scalar field is present, in near extreme conditions, TEH of a rotating short hair black hole cannot be disrupted. Therefore, the value of the parameter $κ$ reveals the connection between rotating short hair black holes and the weak cosmic censorship conjecture, indicating that the presence of short hair significantly affects TEH of black holes. This will aid in further understanding the nature of rotating short hair black holes.

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arXiv2024

Quasinormal modes of dark matter core-black hole spacetime

In the galactic core, when the scale of dark matter is small, the distribution of dark matter is that of a constant density dark matter core.Considering the case of a supermassive black hole coupled to a constant density dark matter core, we study the quasinormal modes of the black hole in the constant density dark matter core black hole system and calculate the quasinormal modes frequency of the black hole using the third order WKB approximation and the prony method.In addition, we study the effect of the constant density dark matter core parameter $r_0$ on the quasinormal modes of black holes in the vicinity of black holes.As the angular quantum number increases, the ringdown process becomes closer and closer to the case of the ringdown process of a schwarzschild black hole.The presence of a constant density dark matter core affects the quasinormal modes of the black hole, with relative deviations on the order of $10^{-15}-10^{-13}$ with respect to the detector.These features suggest that with future improvements in detector accuracy, we can use them for the detection of gravitational waves in the spacetime of constant density dark matter core-black hole systems, which in turn opens up the possibility of understanding the behavior of dark matter in the vicinity of black holes.

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arXiv2024

Modeling the black holes surrounded by a dark matter halo in the galactic center of M87

In this paper, the structure of a dark matter halo can be well described by the mass model of M87 and the Einasto profile for the cold dark matter model, i.e., $ρ_{\text{eina}} (r)=ρ_\text{e} \exp ( -2 α^{-1} ((r/r_\text{e})^α-1 ) )$ (Wang et al. in Nature 585:39-42, 2020). Under these conditions, we construct a solution of a static spherically symmetric black hole in a dark matter halo. Then, using the Newman-janis algorithm, we extend this static solution to the case of rotation, and obtain a solution for the Kerr-like black hole. We prove that this solution of the Kerr-like black hole is indeed a solution to the Einstein field equations. Finally, taking M87 as an example, we study and analyze some physical properties of this Kerr-like black hole, and then compare them with the Kerr black hole. Particularly, from the perspective of the black hole shadow and the fact that the Kerr-like black hole and the Kerr black hole is distinguishable, we give the upper limit of the shape parameter of the Einasto density profile, that is approximately $α<0.22$, which may provide a new method to further improve and perfect the density profile of dark matter model. These research results for the black hole in a dark matter halo may indirectly provide an effective method for detecting the existence of dark matter.

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arXiv2023

Test the Weak Cosmic Supervision Conjecture in Dark Matter-Black Hole System

There is a possibility that the event horizon of a Kerr-like black hole with perfect fluid dark matter (DM) can be destroyed, providing a potential opportunity for understanding the weak cosmic censorship conjecture of black holes. In this study, we analyze the influence of the strength parameter of perfect fluid DM on the destruction of the event horizon of a Kerr-like black hole with spinning after injecting a test particle and a scalar field. We find that, when a test particle is incident on the black hole, the event horizon is destroyed by perfect fluid dark matter for extremal black holes. For nearly extremal black holes, when the dark matter parameter satisfies $α\in \left (-r_{h} , 0\right ) \cup \left ( r_{h} ,k_2\right )$ i.e.$(A<0)$, the event horizon of the black hole will not be destroyed; when the dark matter parameter satisfies $α\in\left ( k_1 ,-r_{h} \right ]\cup \left[0,r_{h}\right ]$ i.e.$(A\ge 0)$, the event horizon of the black hole will be destroyed. When a classical scalar field is incident into the black hole in the extremal black hole case, we find that the range of mode patterns of the scalar field that can disrupt the black hole event horizon is different for different values of the perfect fluid dark matter strength parameter. In the nearly extremal black hole case, through our analysis, we have found when $α\neq0 $ and $α\neq\pm\ r_h$ i.e.$A\neq0$, the event horizon of the black hole can be disrupted. Our research results indicate that dark matter might be capable of breaking the black hole horizon, thus potentially violating the weak cosmic censorship conjecture.

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arXiv2023

Destroying the Event Horizon of a Rotating Black-Bounce Black Hole

For a rotating black hole to be nonsingular, it means that there are no spacetime singularities at its center. The destruction of the event horizon of such a rotating black hole is not constrained by the weak cosmic censorship conjecture, which may provide possibilities to understand the internal structure of black hole event horizons. In this paper, we employ test particles with large angular momentum and a scalar field with large angular momentum to investigate the potential of destroying the event horizon of rotating Black-Bounce black holes. Additionally, we investigate the possibility of destroying the event horizon of a rotating Black-Bounce black hole by considering test particles with large angular momentum and scalar fields with large angular momentum, covering the entire range of the rotating Black-Bounce black hole. We analyze the influence of the parameter m on the possibility of destroying the event horizon in this spacetime. Our analysis reveals that under extreme or near-extreme conditions, the event horizon of this spacetime can potentially be destroyed after the absorption of particles energy and angular momentum, as well as the scattering of scalar fields. Additionally, we find that as the parameter m increases, the event horizon of this spacetime model becomes more susceptible to destruction after the injection of test particles or the scattering of scalar fields.

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arXiv2023

Time-Modulated Intelligent Reflecting Surface for Waveform Security

We consider an OFDM transmitter aided by an intelligent reflecting surface (IRS) and propose a novel approach to enhance waveform security by employing time modulation (TM) at the IRS side. By controlling the periodic TM pattern of the IRS elements, the system is designed to preserve communication information towards an authorized recipient and scramble the information towards all other directions. We introduce two modes of TM pattern control: the linear mode, in which we design common TM parameters for entire rows or columns of the IRS, and the planar mode, where we design TM parameters for each individual IRS unit. Due to the required fewer switches, the linear mode is easier to implement as compared to the planar mode. However, the linear model results in a beampattern that has sidelobes, over which the transmitted information is not sufficiently scrambled. We show that the sidelobes of the linear mode can be suppressed by exploiting the high diversity available in that mode.

eess.SP↗

arXiv2023

Enhance Security of Time-Modulated Array-Enabled Directional Modulation by Introducing Symbol Ambiguity

In this paper, if the time-modulated array (TMA)-enabled directional modulation (DM) communication system can be cracked is investigated and the answer is YES! We first demonstrate that the scrambling data received at the eavesdropper can be defied by using grid search to successfully find the only and actual mixing matrix generated by TMA. Then, we propose introducing symbol ambiguity to TMA to defend the defying of grid search, and design two principles for the TMA mixing matrix, i.e., rank deficiency and non-uniqueness of the ON-OFF switching pattern, that can be used to construct the symbol ambiguity. Also, we present a feasible mechanism to implement these two principles. Our proposed principles and mechanism not only shed light on how to design a more secure TMA DM system theoretically in the future, but also have been validated to be effective by bit error rate measurements.

eess.SP↗

arXiv2023

How secure is the time-modulated array-enabled ofdm directional modulation?

Time-modulated arrays (TMA) transmitting orthogonal frequency division multiplexing (OFDM) waveforms achieve physical layer security by allowing the signal to reach the legitimate destination undistorted, while making the signal appear scrambled in all other directions. In this paper, we examine how secure the TMA OFDM system is, and show that it is possible for the eavesdropper to defy the scrambling. In particular, we show that, based on the scrambled signal, the eavesdropper can formulate a blind source separation problem and recover data symbols and TMA parameters via independent component analysis (ICA) techniques. We show how the scaling and permutation ambiguities arising in ICA can be resolved by exploiting the Toeplitz structure of the corresponding mixing matrix, and knowledge of data constellation, OFDM specifics, and the rules for choosing TMA parameters. We also introduce a novel TMA implementation to defend the scrambling against the eavesdropper.

eess.SP↗

arXiv2023

Gravitational ringing and superradiant instabilities of the Kerr-like black holes in a dark matter halo

Supermassive black holes from the center of galaxy may be immersed in a dark matter halo. This dark matter halo may form a "cusp" structure around the black hole and disappear at a certain distance from the black hole. Based on this interesting physical background, we use the continued fraction method to study gravitational ringring of the Kerr-like black holes immersed in a dark matter halo, i.e., quasinormal modes (QNM) and quasibound states (QBS). We consider these gravitational ringring of black holes both in cold dark matter (CDM) model and scalar field dark matter (SFDM) model at the LSB galaxy, and compare them with Kerr black hole. By testing the states of QNM/QBS frequencies with different parameters $l,m,a$, we confirm the existence of the superradiant instabilities when the black holes both in CDM model and SFDM model. Besides, we also study the impacts of dark matter parameters on the QNM/QBS of black holes at the specific circumstances. In the future, these results may be used for gravitational wave detection of supermassive black holes, and may provide an effective method for detecting the existence of dark matter.

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