arXiv subjects

Yan-Gang Miao

Publications and source records attributed to Yan-Gang Miao.

At least 37 records · Page 2Linked to original sources

arXiv2023

Joule-Thomson effect of AdS black holes in conformal gravity

We investigate the Joule-Thomson effect of AdS black holes in conformal gravity. We derive the Joule-Thomson coefficient in terms of thermodynamic relations and then make an alternative derivation via a direct way. We analyze the Joule-Thomson coefficient and find that the Joule-Thomson coefficients obtained from two different approaches are equal. Moreover, we present a novel isenthalpic process in which the inversion temperature is minimal and it separates the corresponding heating-cooling phase. We analyze the inversion temperature and its corresponding inversion curve that separates the regions for the JT effect to be allowable and forbidden, where such an effect can only be observed in the allowable region. We also discuss the effects of two important parameters on the inversion curves.

gr-qc↗

arXiv2023

Superradiance of massive scalar particles around rotating regular black holes

Regular black holes, as an important attempt to eliminate the singularities in general relativity, have been widely concerned. Due to the fact that the superradiance associated with rotating regular black holes plays an indispensable role in black hole physics, we calculate the superradiance related effects, i.e., the superradiance instability and the energy extraction efficiency for a scalar particle with a small mass around a rotating regular black hole, where the rotating regular black hole is constructed by the modified Newman-Janis algorithm. We analytically give the eigenfrequency associated with instability and the amplification factor associated with energy extraction. For two specific models, the rotating Hayward and Bardeen black holes, we investigate how their regularization parameters affect the growth of instability and the efficiency of energy extraction from the two rotating regular black holes. We find that the regularization parameters give rise to different modes on the superradiance instability and the energy extraction when the rotation parameters are varying. There are two modes for the growth of superradiance instability, and four modes for the energy extraction. Our results show the diversity of superradiance in the competition between the regularization parameter and the rotation parameter for rotating regular black holes.

gr-qc↗

arXiv2023

Regular black holes with improved energy conditions and their analogues in fluids

On the premise of the importance of energy conditions for regular black holes, we propose a method to remedy those models that break the dominant energy condition, e.g., the Bardeen and Hayward black holes. We modify the metrics but ensure their regularity at the same time, so that the weak, null, and dominant energy conditions are satisfied, with the exception of the strong energy condition. Likewise, we prove a no-go theorem for conformally related regular black holes, which states that the four energy conditions can never be met in this class of black holes. In order to seek evidences for distinguishing regular black holes from singular black holes, we resort to analogue gravity and regard it as a tool to mimic realistic regular black holes in a fluid. The equations of state for the fluid are solved via an asymptotic analysis associated with a numerical method, which provides a modus operandi for experimental observations, in particular, the conditions under which one can simulate realistic regular black holes in the fluid.

gr-qc↗

arXiv2023

On heat properties of charged AdS black holes in Gauss-Bonnet gravity coupled with nonlinear electrodynamics

We investigate the heat properties of charged AdS black holes in the Gauss-Bonnet gravity coupled with nonlinear electrodynamics. We consider the thermodynamics of black holes from the perspective of heat capacity and show that the nonlinear electrodynamics can be helpful to improve the thermodynamic stability of black holes. We perform a two-dimensional description in order to reproduce the Hawking temperature, which confirms that the Hawking temperature has an intrinsic topological nature and holds for a higher dimensional spherically symmetric spacetime. We also analyze the Maxwell equal area law and coexistence curve, and find the existence of van der Waals-like phase transitions based on critical exponents. Moreover, we deal with a charged AdS black hole in the Gauss-Bonnet gravity coupled with nonlinear electrodynamics as a working material to study holographic heat engines and obtain an exact expression for the efficiency of a rectangular engine cycle. We then discuss the effects of nonlinear electrodynamics and Gauss-Bonnet couplings on the rectangular engine cycle and compare the efficiency of this cycle with that of the Carnot cycle.

gr-qc↗

arXiv2023

Bounce corrections to gravitational lensing, quasinormal spectral stability and gray-body factors of Reissner-Nordström black holes

Gravitational lensing in the weak field limit, quasinormal spectra, and gray-body factors are investigated in the Reissner-Nordström spacetime corrected by bounce parameters. Using the Gauss-Bonnet theorem, we analyze the effects of bounce corrections to the weak gravitational deflection angle and find that the divergence of the deflection angle can be suppressed by a bounce correction in the Reissner-Nordström spacetime. We also notice that the bounce correction plays the same role as the Morse potential in the deflection angle. Moreover, we derive the perturbation equations with the spin-dependent Regge-Wheeler potential and discuss the quasinormal spectral stability. We observe that the quasinormal spectra decrease for both the massless scalar and electromagnetic field perturbations. We further study the transmission probability of particles scattered by the Regge-Wheeler potential and reveal that the bounce correction introduced into the Reissner-Nordström spacetime increases the gray-body factors of perturbation fields.

gr-qc↗

arXiv2022

Gliner Vacuum, Self-consistent Theory of Ruppeiner Geometry for Regular Black Holes

In the view of the Gliner vacuum, we remove the deformations in the first law of mechanics for regular black holes, where one part of deformations associated with black hole mass will be absorbed into enthalpy or internal energy, and the other part associated with parameters rather than mass will constitute a natural $V$-$P$ term. The improved first law of mechanics redisplays its resemblance to the first law of thermodynamic systems, which implies a restored correspondence of the mechanic variables to the thermodynamic ones. In particular, the linear relation between the entropy and horizon area remains unchanged for regular black holes. Based on the modified first law of thermodynamics, we establish a self-consistent theory of Ruppeiner geometry and obtain a universal attractive property for the microstructure of regular black holes. In addition, the repulsive and attractive interactions inside and outside regular black holes are analyzed in detail.

gr-qc↗

arXiv2022

Noncommutative corrections to the minimal surface areas of the pure AdS spacetime and Schwarzschild-AdS black hole

Based on the perturbation expansion, we compute the noncommutative corrections to the minimal surface areas of the pure AdS spacetime and Schwarzschild-AdS black hole, where the noncommutative background is suitably constructed in terms of the Poincaré coordinate system. In particular, we find a reasonable tetrad with subtlety, which not only matches the metrics of the pure AdS spacetime and Schwarzschild-AdS black hole in the commutative case, but also makes the corrections real rather than complex in the noncommutative case. For the pure AdS spacetime, the nocommutative effect is only a logarithmic term, while for the Schwarzschild-AdS black hole, it contains a logarithmic contribution plus both a mass term and a noncommutative parameter related term. Furthermore, we show that the holographic entanglement entropy with noncommutativity obeys a relation which is similar to the first law of thermodynamics in the pure AdS spacetime.

hep-th↗

arXiv2022

Internal structure and its connection with thermodynamics and dynamics in black holes

In general, a finite metric function at the center of a black hole describes a non-singular spacetime but an infinite metric at the center gives a singular spacetime, where the former is associated with convergent Ricci and Kretschmann scalars together with complete radial geodesics, while the latter is related to divergent Ricci and Kretschmann scalars together with incomplete radial geodesics. For the charged black hole in the four-dimensional Einstein-Gauss-Bonnet theory, we find that its metric function is finite at its center in one region of parameters but complex in the other region of parameters. The finite case describes a strange spacetime which presents the Ricci and Kretschmann scalars of a singular spacetime and the radial geodesics of a non-singular spacetime, while the complex case gives rise to the similar situation. We verify that the cosmic censorship conjecture is maintained for the black hole model. Further, we investigate the second-order phase transition, quasinormal modes of perturbation of a test scalar field in the eikonal limit, and shadow radius for the black hole and find that the thermodynamic and dynamic properties depend on the metrics. In this way, we connect the internal structure with the thermodynamics and dynamics for this black hole. Moreover, we compare such a black hole of modified gravity with the Reissner-Nordström black hole of Einstein's general relativity in these thermodynamic and dynamic properties.

gr-qc↗

arXiv2022

Charged black-bounce spacetimes: Photon rings, shadows and observational appearances

The photon ring, shadow and observational appearance of the emission originating near a charged black-bounce are investigated. Based on the geodesic analysis, we determine the upper and lower limits of critical impact parameters of a charged black-bounce. In particular, we find that the charged black-bounce shares the same critical impact parameter with the Reissner-Nordstöm black hole. In addition, we classify the light trajectories coming from the region near the charged black-bounce by utilizing the rays tracing procedure, and then investigate the observational appearance of the emissions from a thin disk accretion and a spherically symmetric infalling accretion. We reveal that a large charge increases the observed intensity but decreases the apparent size of shadows, and that the photon ring presents the intrinsic property of a spacetime geometry, which is independent of the types of the two accretions. Our results are in good agreement with the recent observations.

gr-qc↗

arXiv2022

The generalized holographic $c$-function for regular AdS black holes

We use the causal horizon entropy to study the asymptotic behaviors of regular AdS black holes. In some literature, the causal horizon entropy is regarded as a generalized holographic $c$-function. In this paper, we apply this idea to the case of regular AdS black holes. We show that the causal horizon entropy decreases to zero at the center of regular AdS black holes and in particular it is stationary because its derivative with respect to the affine parameter approaches zero asymptotically. Meanwhile, the asymptotic behavior of the metric of regular AdS black holes implies that the black hole center corresponds to an IR fixed point. Therefore, we conclude that the causal horizon entropy is a valid candidate for the holographic $c$-function of these regular AdS black holes.

hep-th↗

arXiv2022

Weinhold geometry and thermodynamics of Bardeen AdS black holes

Thermodynamics of Bardeen AdS black holes has attracted a great deal of attentions due to its intrinsic complications and rich phase structures. However, the entropy and thermodynamic volume are incorrect in some literatures. In this paper we revisit the thermodynamics of Bardeen AdS black holes and provide the correct entropy and thermodynamic volume. Furthermore, thermodynamic geometries are a powerful tool to probe the microstructure of black holes. Based on the Hessian matrix of black hole mass, we introduce a thermodynamic metric and give its scalar curvature in Weinhold's geometry. The conformal relation between Weinhold's geometry and Ruppeiner's geometry will be changed due to the specific first law of thermodynamics for regular black holes like the Bardeen AdS black hole. We also investigate the critical behaviour of phase transitions in an extended phase space, and find that the critical behaviour of the Bardeen AdS black hole coincides with that of liquid-gas systems. In particular, based on the Weinhold geometry we unveil a repulsive interaction in the microstructure of the Bardeen AdS black hole under its small volume state, while it is known that only attractive interaction exists in the microstructure of the van der Waals fluid.

gr-qc↗

arXiv2022

Acoustic regular black hole in fluid and its similarity and diversity to a conformally related black hole

We address an interesting question in the present paper that whether the acoustic gravity can be applied as a tool to the study of regular black holes. For this purpose, we construct a general acoustic regular black hole in the spherically symmetric fluid, where its regularity is verified from the perspective of finiteness of curvature invariants and completeness of geodesics. In particular, we find that the acoustic interval not only looks like a line element of a conformally related black hole in which the fluid density can be regarded as a conformal factor, but also gives rise to a non-vanishing partition function which coincides with that of a conformally related black hole. As an application, we provide a specific acoustic regular black hole model, investigate its energy conditions and compute its quasinormal modes. We note that the strong energy condition of our model is violated completely outside the horizon of the model but remains valid in some regions inside the horizon, which may give a new insight into the relation between the regularity and strong energy condition. Moreover, we analyze the oscillating and damping features of our model when it is perturbed.

gr-qc↗

arXiv2022

Absorption cross section of regular black holes in scalar-tensor conformal gravity

In terms of the complex angular momentum method, we compute the absorption cross section by analyzing a massless test scalar field around conformally related black holes. At first, we investigate circular null geodesics and thereby prove a precondition for calculating the absorption cross section in the context of conformally related black holes. Then we use the WKB approximation method to derive the analytic expression of Regge frequency and the oscillation part of absorption cross sections. We find that this oscillation part depends on the scale factor of conformal transformations. By taking the conformally related Schwarzschild-Tangherlini black hole as an example, we show that this regular black hole has substantially distinctive absorption behavior compared with singular black holes. Our result provides a new approach to distinguish a regular black hole from a singular one.

gr-qc↗

arXiv2022

Higher-dimensional regular Reissner-Nordström black holes associated with linear electrodynamics

Following the interpretation of matter source that the energy-momentum tensor of anisotropic fluid can be dealt with effectively as the energy-momentum tensor of perfect fluid plus linear (Maxwell) electromagnetic field, we obtain the regular higher-dimensional Reissner-Nordström (Tangherlini-RN) solution by starting with the noncommutative geometry inspired Schwarzschild solution. Using the boundary conditions that connect the noncommutative Schwarzschild solution in the interior of the charged perfect fluid sphere to the Tangherlini-RN solution in the exterior of the sphere, we find that the interior structure can be reflected by the exterior parameter, the charge-to-mass ratio. Moreover, we investigate the stability of the boundary under mass perturbation and indicate that the new interpretation imposes a rigid restriction upon the charge-to-mass ratio. This restriction, in turn, permits a stable noncommutative black hole only in the 4-dimensional spacetime.

hep-th↗

arXiv2021

Can we know about black hole thermodynamics through shadows?

We investigate the relationship between shadow radius and microstructure for a general static spherically symmetric black hole and confirm their close connection. In this regard, we take the Reissner-Nordström (AdS) black hole as an example to do the concrete analysis. On the other hand, we study for the Kerr (AdS) black hole the relationship between its shadow and thermodynamics in the aspects of phase transition and microstructure. Our results for the Kerr (AdS) black hole show that the shadow radius $r_{\rm sh}$, the deformation parameters $δ_s$ and $k_s$, and the circularity deviation $ΔC$ can reflect the black hole thermodynamics. In addition, we give the constraints to the relaxation time of the M$87^{*}$ black hole by combining its shadow data and the Bekenstein-Hod universal bounds when the M$87^{*}$ is regarded as the Reissner-Nordström or Kerr black hole. We predict that the minimum relaxation times of M$87^{*}$ black hole and Sgr $A^{*}$ black hole are approximately 3 days and 2.64 minutes, respectively. Finally, we draw the first graph of the minimum relaxation time $τ_{\rm min}$ with respect to the maximum shadow radius $ r_{\rm sh}^{\rm max}$ at different mass levels.

gr-qc↗

arXiv2021

Quasinormal Modes and Thermodynamics of Regular Black Holes

By applying the dimensionless scheme, we investigate the quasinormal modes and phase transitions analytically for three types of regular black holes. The universal deviations to the first law of mechanics in regular black holes are proved. Meanwhile, we verify that second order phase transitions and Davies points still exist in these three models. In addition, we calculate their quasinormal modes in the eikonal limit by applying the light ring/quasinormal mode correspondence, and discuss the spiral-like shapes and the relations between the quasinormal modes and phase transitions. As the main result, we show that spiral-like shapes in the complex frequency plane are closely related to the parameterization, namely in some particular units the spiral-like shapes will emerge in the models, which may not be of the spiral behaviors reported by other authors. We also discover a universal property of regular black holes, i.e., the imaginary parts of their QNMs do not vanish for the extreme cases, which does not appear in singular black holes, such as the Reissner-Nordström and Kerr black holes, etc.

gr-qc↗

arXiv2021

High-dimensional Schwarzschild black holes in scalar-tensor-vector gravity theory

We obtain a high-dimensional Schwarzschild black hole solution in the scalar-tensor-vector gravity (STVG), and then analyze the influence of parameter $α$ associated with a deviation of the STVG theory from General Relativity on event horizons and Hawking temperature. We calculate the quasinormal mode frequencies of massless scalar field perturbations for the high-dimensional Schwarzschild STVG black hole by using the sixth-order WKB approximation method and the unstable null geodesic method in the eikonal limit. The results show that the increase of parameter $α$ makes the scalar waves decay slowly, while the increase of the spacetime dimension makes the scalar waves decay fast. In addition, we study the influence of parameter $α$ on the shadow radius of this high-dimensional Schwarzschild STVG black hole and find that the increase of parameter $α$ makes the black hole shadow radius increase, but the increase of the spacetime dimension makes the black hole shadow radius decrease. Finally, we investigate the energy emission rate of the high-dimensional Schwarzschild STVG black hole, and find that the increase of parameter $α$ makes the evaporation process slow, while the increase of the spacetime dimension makes the process fast.

gr-qc↗

arXiv2021

Distinct thermodynamic and dynamic effects produced by scale factors in conformally related Einstein-power-Yang-Mills black holes

We study the thermodynamics and dynamics of high-dimensional Einstein-power-Yang-Mills black holes in conformal gravity. Specifically, we investigate a class of conformally related black holes whose metrics differ by a scale factor. We show that a suitable scale factor cures the geodesic incompleteness and the divergence of Kretschmann scalars at the center of black holes. In the aspect of thermodynamics, we analyse the Hawking temperature, the entropy, and the specific heat, and verify the existence of second-order phase transitions. We find that the thermodynamics of this class of conformally related black holes is independent of scale factors. In the aspect of dynamics, we find that the quasinormal modes of minimally coupled scalar field perturbations are dependent on scale factors. Quite interesting is that the behavior of quasinormal mode frequencies also supports the independence of scale factors for the second-order phase transitions. Our results show that the scale factors produce distinct thermodynamic and dynamic effects in the conformally related Einstein-power-Yang-Mills black holes, which provides an interesting connection between thermodynamics and dynamics of black holes in conformal gravity.

gr-qc↗