arXiv subjects

Xin-Yang Wang

Publications and source records attributed to Xin-Yang Wang.

13 recordsLinked to original sources

arXiv2026

Novel extended inner shadow in images of Johannsen-Psaltis black holes with thin accretion disks

The Johannsen-Psaltis (JP) metric is constructed by introducing deviation parameters into the Kerr metric. The presence of these deviation parameters provides additional degrees of freedom for testing the extent to which astrophysical black holes are consistent with the Kerr paradigm and for examining the validity of the no-hair theorem. Since black hole imaging provides one of the most direct means of probing the properties of astrophysical black holes, a detailed investigation of the imaging characteristics of JP black holes constitutes a natural first step toward employing the JP metric to explore potential deviations from the Kerr geometry in astrophysical black hole systems. Accordingly, numerical backward ray-tracing simulations are employed to conduct a comprehensive investigation of the image structures, intensity distributions, and redshift-blueshift signatures of JP black holes with both closed and non-closed event horizons. The dependence of these imaging characteristics on the deviation parameter is also investigated systematically. Furthermore, the emergence of an extended inner shadow, distinct from the original inner shadow of the black hole, in images of JP black holes with non-closed event horizons motivated a detailed investigation of its physical formation mechanism using both numerical backward ray-tracing simulations and an approximate analytical framework.

gr-qc↗

arXiv2026

Imprints of the Lorentz-symmetry breaking on the precessing jet nozzle of M87*

The approximately 11-year jet precession period observed in M87* strongly suggests that the supermassive rotating black hole with a tilted accretion disk, which could provide a powerful constraint for confining the parameters of black hole. In this paper, our aim is to utilize the observations of M87* to preliminarily constrain the parameters of the rotating black hole in Bumblebee gravity by modeling the motion of the tilted accretion disk particle with the spherical orbits. We compute spherical orbits and ISSOs, demonstrating that the conserved quantities energy $\mathcal{E}$, angular momentum $\mathcal{L}$, and Carter constan $\mathcal{K}$ depend on $(r,a,\ell,ζ)$, exhibiting distinct behaviors for prograde and retrograde orbits. For prograde orbits, the ISSO radius $r_{ISSO}$ decreases with spin parameter $a$ and LSB parameter $\ell$ and increases with the tilt angular $ζ$, whereas the opposite trends occur for retrograde orbits. Angular analysis shows that $θ$ oscillates within $(π/2-ζ, π/2+ζ)$, while $ϕ$ increases approximately linearly, enabling the determination of the oscillation period $T_θ$, azimuthal accumulation $ϕ(T_θ)/π$, and precession angular velocity $ω_t$. Using the observed jet precession period $T=11.24 \pm 0.47$ years with a fixed tilt $ζ=1.25^\circ$, the warp radius $r/M$ ranges from $(5.73,25.15)$ for prograde and $(6.16,26.46)$ for retrograde orbits, increasing with $a$ or $\ell$. Comparisons with Kerr limits ($r/M=14.12$ prograde, $16.1$ retrograde) suggest that $r/M>16$ may indicate a non-vacuum Bumblebee vector field. Incorporating the EHT shadow $θ_{sh}=42\pm3μ$as further constrains $r/M$ to $(5.82,22.61)$ and $(6.17,24.74)$, with discrepancies of $0.05\sim1.96$.

gr-qc↗

arXiv2025

The characteristics of circular motion and quasiperiodic oscillations around accelerating black hole

{This study explores the motion of massive test particles and associated quasi-periodic oscillations (QPOs) around an accelerating black hole. The acceleration factor $A$ suppresses the radial effective potential $V_{\text{eff}}$, thereby lowering the energy $E$ and angular momentum $L$ required for stable circular orbits. Stability demands $\partial_r^2 V_{\text{eff}} \geq 0$, setting an upper bound $AM$ $\leq 0.0161$. As $A$ increases, the innermost stable circular orbit (ISCO) radius grows, while $L_{\text{ISCO}}$ and $E_{\text{ISCO}}$ decrease. Radiative efficiency $ε$ rises with $A$, peaking at $6.9\%$. Fundamental frequencies show that $A$ accelerates the decay of the Keplerian $Ω_ϕ$ and vertical $Ω_θ$ frequencies, while suppressing the radial frequency. The divergence between $Ω_θ$ and $Ω_ϕ$ increases with $A$, differing from spherical black hole behavior. Using the RP, ER3, ER4, and WD QPO models, the WD model predicts the highest frequencies. The resonant radius of ER4 model remains fixed across frequency ratios, unlike ER3. Although $A$ suppresses twin-peak QPO frequencies, it enhances the nodal precession frequency $ν_{\text{nod}}$. Fitting observational data from GRO J1655-40 and XTE J1859+226 and applying the TOV limit, the ER4 model uniquely fits GRO J1655-40 with $(10^3A, M, r/M) \approx (4.31, 3.43 M_\odot, 8.08)$. For XTE J1859+226, three models yield $10^3A \approx 1.4$, excluding ER3, suggesting stronger acceleration in GRO J1655-40.}

gr-qc↗

arXiv2025

Second Law of Black Holes Thermodynamics in Non-Quasi-Static Processes

The Bekenstein-Hawking entropy satisfies the generalized second law of black hole thermodynamics for arbitrary thermodynamic evolution within Einstein-Maxwell theory. In contrast, the black hole entropy that satisfies the second law in low-energy effective modified gravity theories related to quantum gravity is derived solely by considering linear perturbations within quasi-static processes. Since astrophysical processes are typically non-quasi-static, deriving a rigorous expression for entropy within the quasi-static framework is not feasible. By treating the effective quantum corrections as first-order perturbations, the black hole entropy in Einstein-Maxwell gravity with generalized quadratic corrections for arbitrary dynamical processes is derived. This entropy is distinct from the Iyer-Wald and Dong-Wald entropies and is applicable to non-quasi-static processes. Furthermore, it is shown that the black hole entropy is consistent with the generalized covariant entropy boundary. This work establishes a framework for examining the generalized second law of black hole thermodynamics in non-static processes within modified gravity theories.

gr-qc↗

arXiv2025

Revisiting the shadow of Johannsen-Psaltis black holes

The Johannsen-Psaltis (JP) metric provides a robust framework for testing the no-hair theorem of astrophysical black holes due to the regular spacetime configuration around JP black holes. Verification of this theorem through electromagnetic spectra often involves analyzing the photon sphere near black holes, which is intrinsically linked to black hole shadows. Investigating the shadow of JP black holes offers an effective approach for assessing the validity of theorem. Since the Hamilton-Jacobi equation in the JP metric does not permit exact variable separation, an approximate analytical approach is employed to calculate the shadow, while the backward ray-tracing numerical method serves as a rigorous alternative. For JP black holes with closed event horizons, the approximate analytical approach reliably reproduces results obtained through the numerical computation. However, significant discrepancies emerge for black holes with non-closed event horizons. As the deviation parameter $ε_3$ increases, certain regions of the critical curve transition into non-smooth configurations. Analysis of photon trajectories in these regions reveals chaotic dynamics, which accounts for the failure of the approximate analytical method to accurately describe the shadows of JP black holes with non-closed event horizons.

gr-qc↗

arXiv2024

Masses of the conjectured H-dibaryon at different temperatures

We present a lattice QCD determination of masses of the conjectured H-dibaryon $m_H$ at nine different temperatures $T/T_c =0.24, 0.63, 0.76, 0.84, 0.95, 1.09, 1.27, 1.52, 1.90$. In the meantime, the masses of baryon $N$, $Σ$, $Ξ$ and $Λ$ at different temperatures are also computed. The simulation is performed on anisotropic lattice with $N_f=2+1$ flavours of clover fermion at quark mass which corresponds to $m_π=384(4) {\rm MeV} $. The thermal ensembles were provided by the FASTSUM collaboration and the zero temperature ensembles by the Hadspec collaboration. We also calculate the spectral density of the correlation function of those particles. The spectral density distributions show rich peak structure at the lowest temperature, while at intermediate temperatures, the mass values of those particles obtained by extrapolation method reflect a two-peak structure. While the spectral density for octet baryon becomes smooth at $T/T_c = 1.27, 1.52, 1.90$, the spectral density for H-dibaryon becoms smooth at $T/T_c = 1.90$. At $T/T_c =0.24 $, the mass difference of H-dibaryon and $Λ$ pair $Δm = m_H - 2\,m_Λ $ is estimated to be $Δm = -14.6(6.2) {\rm MeV}$ which suggests there exists a bound H-dibaryon state.

hep-lat↗

arXiv2024

Active formation of Friedrich-Wintgen bound states in the continuum in dielectric dimerized grating borophene heterostructure

The Friedrich-Wintgen bound state in the continuum (FW BIC) provides a unique approach for achieving high quality factor (Q-factor) resonance, which has attracted wide attention and promoted the development of various applications. However, the FW BIC is usually considered as accident BIC resulting from the continuous parameters tuning, and a systematic approach to generate the FW BIC is still lacking. To address this, a method of actively forming FW BIC by matching the damping rate and resonance frequency of the coupling mode is proposed. As a proof-of-principle example, we propose a dielectric dimerized grating borophene heterostructure that generates a FW BIC near the commercially important communication wavelength. The coupling system comprises an electrically tunable borophene plasmon mode and a BIC supported by a dielectric dimer grating that can be attributed to the Brillouin zone folding. More interestingly, the BIC can be excited by the localized borophene plasmon (LBP) mode through near-field coupling as LBP mode can be considered as the dipole source. The interaction between them can further form the FW BIC, and support electromagnetically induced transparency (EIT)-like with maximum group index up to 2043, indicating its great potential for slow light applications. Our results provide a promising strategy and theoretical support for the generation of FW BIC in active plasmonic optical devices.

physics.optics↗

arXiv2022

The linearized second law for any higher curvature gravity with the scalar and the electromagnetic fields

The first law of black hole thermodynamics is suitable for any diffeomorphism invariant gravity, and the entropy in the first law is the Wald entropy which is highly dependent on the non-minimal coupling interactions in the theory of gravity. However, whether the Wald entropy still satisfies the second law needs to be investigated. The entropy of black holes obeying the linearized second law in arbitrary high-order curvature gravity is given, which can be written as the Wald entropy with correction terms. It indicates that the Wald entropy is not commonly obeying the linearized second law for any high-order curvature gravity. When the interactions of gravity with matter fields are included in the theory of gravity, the entropy of black holes obeying the linearized second law has not been obtained in this case. Considering any high-order curvature gravity with the scalar and the electromagnetic fields, from the Raychaudhuri equation, the entropy obeying the linearized second law is generally obtained, which can be expressed as the Wald entropy with correction terms as well. The entropy does not include the contribution from the electromagnetic fields, and the correction terms contain the contribution from the minimal coupling interaction between gravity and the scalar fields. Since the entropy satisfying the linearized second law depends only on the non-minimal coupling interaction of gravity in previous research, this result upends our understanding of the entropy of black holes obeying the linearized second law in any gravitational theory with matter fields.

gr-qc↗

arXiv2021

Generalized proof of the linearized second law in general quadric corrected Einstein-Maxwell gravity

Although the entropy of black holes in any diffeomorphism invariant theory of gravity can be expressed as the Wald entropy, the issue of whether the entropy always obeys the second law of black hole thermodynamics remains open. Since the nonminimal coupling interaction between gravity and the electromagnetic field in the general quadric corrected Einstein-Maxwell gravity can sufficiently influence the expression of the Wald entropy, we check whether the Wald entropy of black holes in the quadric corrected gravity still satisfies the second law. A quasistationary accreting process of black holes is first considered, which describes that black holes are perturbed by matter fields and eventually settle down to a stationary state. Two assumptions that the matter fields should obey the null energy condition and that a regular bifurcation surface exists on the background spacetime are further proposed. According to the two assumptions and the Raychaudhuri equation, we demonstrate that the Wald entropy monotonically increases along the future event horizon under the linear order approximation of the perturbation. This result indicates that the Wald entropy of black holes in the quadric corrected gravity strictly obeys the linearized second law of thermodynamics.

gr-qc↗

arXiv2020

Investigating the Linearized Second Law in Horndeski Gravity

Since the entropy of stationary black holes in Horndeski gravity will be modified by the non-minimally coupling scalar field, a significant issue of whether the Wald entropy still obeys the linearized second law of black hole thermodynamics can be proposed. To investigate this issue, a physical process that the black hole in Horndeski gravity is perturbed by the accreting matter fields and finally settles down to a stationary state is considered. According to the two assumptions that there is a regular bifurcation surface in the background spacetime and that the matter fields always satisfy the null energy condition, one can show that the Wald entropy monotonically increases along the future event horizon under the linear order approximation without any specific expression of the metric. It illustrates that the Wald entropy of black holes in Horndeski gravitational theory still obeys the requirement of the linearized second law. Our work strengthens the physical explanation of Wald entropy in Horndeski gravity and takes a step towards studying the area increase theorem in the gravitational theories with non-minimal coupled matter fields.

gr-qc↗

arXiv2020

Examining the weak cosmic censorship conjecture of RN-AdS black holes via the new version of the gedanken experiment

Based on the new version of the gedanken experiment proposed by Sorce and Wald, we investigate the weak cosmic censorship conjecture (WCCC) for a Reissner-Nordström-Anti-de Sitter (RN-AdS) black hole under the perturbation of extra matter fields. Firstly, we propose that the cosmological constant can be effectively derived from the matter fields and its value varies with the matter fields perturbing the black hole. Meanwhile, we assume that the perturbation satisfies the stability condition. This condition means that after a long time of the perturbation, the black hole solution also belongs to the family of the RN-AdS solution. After that, based on both the stability condition and the null energy condition, while using the off-shell variation method, the first-order and the second-order perturbation inequalities are derived respectively when the cosmological constant is considered as a dynamic variable. It is the first time to extend the two perturbation inequalities to contain the term of the press and volume of thermodynamics. Finally, we perform the two perturbation inequalities into testing the WCCC for the RN-AdS black hole under the second-order approximation of the perturbation. It is shown that if the variation of the cosmological constant is caused by the matter fields, while the stability condition and the null energy condition are all satisfied, the black hole cannot be destroyed after the perturbation. In other words, the WCCC for the RN-AdS black hole is valid under the second-order approximation of the perturbation.

hep-th↗

arXiv2020

Gedanken experiments at high-order approximation: nearly extremal Reissner-Nordstrom black holes cannot be overcharged

The new version of the gedanken experiment proposed by Sorce and Wald has been used to examine the weak cosmic censorship conjecture (WCCC) for black holes at the second-order approximation of the matter fields perturbation. However, only considering the perturbation until the second-order approximation is incomplete because there is an optimal option such that the existing condition of the event horizon vanishes at second-order. For this circumstance, we cannot judge whether the WCCC is satisfied at this order. In our investigation, the $k$th-order perturbation inequality is generally derived. Using the inequalities, we examine the WCCC for nearly extremal Reissner-Nordstöm black holes at higher-order approximation. It is shown that the WCCC cannot be violated yet after the perturbation. From this result, it can be indicated that the WCCC is strictly satisfied at the perturbation level for nearly extremal RN black holes.

hep-th↗

arXiv2018

Entropy in the interior of a Kerr black hole

Christodoulou and Rovelli have shown that the maximal interior volume of a Schwarzschild black hole linearly grows with time. Recently, their conclusion has been extended to the Reissner{-}Nordstr$\ddot{\text{o}}$m and Kerr black holes. Meanwhile, the entropy of interior volume in a Schwarzschild black hole has also been calculated. Here, a new method calculating the entropy of interior volume of the black hole is given and it can be used in more general cases. Using this method, the entropy associated with the volume of a Kerr black hole is calculated and it is found that the entropy is proportional to the Bekenstein-Hawking entropy in the early stage of black hole evaporation. Using the differential form, the entropy of interior volume in a Schwarzschild black hole is recalculated. It is shown that the proportionality coefficient between the entropy and the Bekenstein-Hawking entropy is half of that given in the previous literature. Moreover, the black hole information paradox is brought up again and discussed.

gr-qc↗