arXiv subjects

Deyou Chen

Publications and source records attributed to Deyou Chen.

At least 37 records · Page 2Linked to original sources

arXiv2023

Gravitational Lensing by Transparent Janis-Newman-Winicour Naked Singularities

The Janis-Newman-Winicour (JNW) spacetime can describe a naked singularity with a photon sphere that smoothly transforms into a Schwarzschild black hole. Our analysis reveals that photons, upon entering the photon sphere, converge to the singularity in a finite coordinate time. Furthermore, if the singularity is subjected to some regularization, these photons can traverse the regularized singularity. Subsequently, we investigate the gravitational lensing of distant sources and show that new images emerge within the critical curve formed by light rays escaping from the photon sphere. These newfound images offer a powerful tool for the detection and study of JNW naked singularities.

gr-qc↗

arXiv2023

Two non-perturbative $α^{\prime}$ corrected or loop corrected string cosmological solutions

In this paper, we present two non-perturbative string cosmological solutions without curvature singularities for the bosonic gravi-dilaton system. These solutions are general in the sense that they can straightforwardly match the perturbative solution to arbitrarily high orders in the perturbative region. The first solution includes non-perturbative $α'$ corrections based on Hohm-Zwiebach action. We then use the simple phenomenological map between $α^{\prime}$ corrected theory and loop corrected theory in string cosmology to construct a non-perturbative loop corrected non-singular solution. Both solutions are non-singular everywhere. Therefore, the pre- and post-big-bangs are smoothly connected by these solutions.

hep-th↗

arXiv2023

Spatial regions, chaos bound and its violation

The influence of the angular momentum of the particle on the Lyapunov exponent has been studied. In this paper, we investigate influences of the charge and angular momentum of a particle around non-extremal and extremal Reissner-Nordström black holes with a scalar hair on the exponent, and find spatial regions where the chaos bound is violated for certain values of the black holes' parameters. The exponent is gotten by calculating the eigenvalue of a Jacobian matrix in a phase space. The violation occurs from the nea-horizon regions to certain distances from the event horizons. When the charge or angular momentum of the particle are fixed at certain values, the spatial regions increase with the increase of the hair parameter's value when the black hole's charge is fixed, and with the increase of the black hole's charge when the hair parameter is fixed. For the extremal black hole, the violation can occur very close to the horizon when the particle's charge is large enough.

hep-th↗

arXiv2022

Angular momentum and chaos bound of charged particles around Einstein-Euler-Heisenberg AdS black holes

In this paper, we investigate influences of the charge and angular momentum of a particle around a charged Einstein-Euler-Heisenberg AdS black hole on a Lyapunov exponent, and find spatial regions where the chaos bound is violated. Positions of circular orbits are gotten by fixing the charge and angular momentum of the particle, respectively. The positions gradually move away from the event horizon with the increase of the angular momentum when the charge is fixed and with the decrease of the charge when the angular momentum is fixed. For certain values of the charge, angular momentum and Euler-Heisenberg parameter, the spatial regions where the bound is violated are found. When the charge is fixed and the Euler-Heisenberg parameter is large, a small angular momentum causes the violation. Although the angular momentum is small, the corresponding spatial region is not small. An interesting discovery is that the bound is violated by the black hole when the particle's charge is less than 1 and $Λ=0$, but this requires the black hole's charge to be large enough. This violation may be related to the dynamical stability of the black hole. The backreaction of the particle on the background spacetime isn't considered in the investigation.

hep-th↗

arXiv2022

Bound on Lyapunov exponent in Einstein-Maxwell-Dilaton-Axion black holes

In this paper, we investigate the influence of the angular momentum of a charged particle around non-extremal and extremal Einstein-Maxwell-Dilaton-Axion black holes on the Lyapunov exponent. The angular momentum's ranges and spatial regions where the bound of the exponent is violated are found for certain values of the rotation parameter and dilatonic constant of the black holes. This violation always exists when the rotation parameter is large enough and the rotation directions of the particle is opposite to those of the black holes. The spatial regions outside the extermal black hole for the violation is relatively large. In the near-horizon regions of the extremal black holes, the violation depends on the rotation directions of the black holes and particle, and does not depend on the value of the angular momentum.

hep-th↗

arXiv2022

Quasinormal modes and the correspondence with shadow in black holes with a deficit solid angle and quintessence-like matter

In this paper, we investigate the photon sphere, shadow radius and quasinormal modes of a $4$-dimensional black hole with a deficit solid angle and quintessence-like matter. We find that the radii of the photon sphere and shadow decrease with the decreases of the deficit solid angle and density of quintessence-like matter. The quasinormal modes are gotten by the sixth order WKB approximation method and shadow radius, respectively. The values of the real part and imaginary parts of the quasinormal modes increase with the decrease of the values of the deficit solid angle and density of quintessence-like matter when the multipole number is fixed. The quasinormal modes gotten by these two methods are in good agreement, especially when the multipole number is large. It shows the correspondence between the quasinormal modes in the eikonal limit and shadow.

gr-qc↗

arXiv2022

Chaos bound and its violation in charged Kiselev black hole

The chaos bound in the near-horizon regions has been studied through the expansions of the metric functions on the horizon. In this paper, we investigate the chaos bound in the the near-horizon region and at a certain distance from the horizon of a charged Kiselev black hole. The value of the Lyapunov exponent is accurately calculated by a Jacobian matrix. The angular momentum of a charged particle around the black hole affects not only the exponent, but also the position of the equilibrium orbit. This position gradually moves away from the horizon with the increase of the angular momentum. We find that the the bound is violated at a certain distance from the horizon and there is no violation in the near-horizon region when the charge mass ratio of the particle is fixed. The small value of the normalization factor is more likely to cause the violation.

gr-qc↗

arXiv2021

Quasinormal modes and the correspondence with shadow in a charged black hole in presence of quintessence

In this paper, we investigate the photon sphere, shadow radius and quasinormal modes of a charged black hole in presence of quintessence. The result shows that the shadow radius decreases with the increase of the electric charge. The quasinormal modes are derived by the sixth WKB approximation method and shadow radius, respectively. For the fixed electric charge and multipole number, the values of the real and imaginary parts of the quasinormal modes decrease with the increase of the quintessence charge. When the value of the multipole number is large, the quasinormal modes derived by the two methods are consistent, which shows the correspondence between the quasinormal modes in the eikonal limit and shadow. When the value of the multipole number is small, the quasinormal modes obtained by the two methods are also in good agreement.

gr-qc↗

arXiv2021

The correspondence between shadow and test field in a four-dimensional charged Einstein-Gauss-Bonnet black hole

In this paper, we investigate the photon sphere, shadow radius and quasinormal modes of a four-dimensional charged Einstein-Gauss-Bonnet black hole. The perturbation of a massless scalar field in the black hole's background is adopted. The quasinormal modes are gotten by the $6th$ order WKB approximation approach and shadow radius, respectively. When the value of the Gauss-Bonnet coupling constant increase, the values of the real parts of the quasinormal modes increase and those of the imaginary parts decrease. The coincidence degrees of quasinormal modes derived by the two approaches increases with the increase of the values of the Gauss-Bonnet coupling constant and multiple number. It shows the correspondence between the shadow and test field in the four-dimensional Einstein-Gauss-Bonnet-Maxwell gravity. The radii of the photon sphere and shadow increase with the decrease of the Gauss-Bonnet coupling constant.

gr-qc↗

arXiv2020

Remarks on the weak cosmic censorship conjecture of RN-AdS black holes with cloud of strings and quintessence under the scalar field

In this paper, we investigate the thermodynamics and weak cosmic censorship conjecture in a RN-AdS black hole with the cloud of strings and quintessence by the scattering of a scalar field. The variations of the thermodynamic variables are calculated in the normal and extended phase spaces. In the normal phase space, where the cosmological constant is considered as a constant, the first and second laws of thermodynamics are satisfied. In the extended phase space, where the cosmological constant and the parameters related to the cloud of strings and quintessence are treated as variables, the first law of thermodynamics is still satisfied and the second law of thermodynamics is indefinite. Moreover, we find that the weak cosmic censorship conjecture is valid for the extremal and near-extremal black holes in both phase spaces.

gr-qc↗

arXiv2020

Thermodynamic extremality relations in the massive gravity

A universal relation between the leading correction to the entropy and extremality was gotten in the work of Goon and Penco. In this paper, we extend this work to the massive gravity and investigate thermodynamic extremality relations in a topologically higher-dimensional black hole. A rescaled cosmological constant is added to the action of the massive gravity as a perturbative correction. This correction modifies the extremality bound of the black hole and leads to the shifts of the mass, entropy, etc. The Goon-Penco relation is gotten. Regarding the cosmological constant as a variable related to pressure, we get the thermodynamic extremality relations between the mass and pressure, charge, parameters $c_i$ by accurate calculations, respectively. Finally, these relations are verified by a triple product identity, which shows that the universal relation exists in black holes.

gr-qc↗

arXiv2020

Overcharging problem and thermodynamics in extended phase spaces

In this paper, the overcharging problem and thermodynamics in the extended phase spaces of the five-dimensional spherically symmetric topological black holes are investigated by absorptions of scalar particles and fermions. The cosmological constant is regarded as a variable related to pressure and its conjugate quantity is a thermodynamic volume. The first law of thermodynamics is recovered. The second law is violated in the extended phase space of the extremal and near-extremal black holes. The overcharging problem is tested by the existence of the event horizons. The event horizon is determined by the metric component $f(r)$. The minimal values of the metric component at the final stage show that the extremal and near-extremal black holes can not be overcharged.

gr-qc↗

arXiv2019

Weak cosmic censorship conjecture in BTZ black holes with scalar fields

The weak cosmic censorship conjecture in the near-extremal BTZ black hole has been tested by the test particles and fields. It was claimed that this black hole could be overspun. In this paper, we review the thermodynamics and weak cosmic censorship conjecture in BTZ black holes by the scattering of the scalar field. The first law of thermodynamics in the non-extremal BTZ black hole is recovered. For the extremal and near-extremal black holes, due to the divergence of the variation of the entropy, we test the weak cosmic censorship conjecture by evaluating the minimum values of the function $f$. Both of the extremal and near-extremal black holes cannot be overspun.

gr-qc↗

arXiv2019

Thermodynamics and weak cosmic censorship conjecture in Reissner-Nordstr$\ddot{o}$m anti-de Sitter black holes with scalar field

The thermodynamics and weak cosmic censorship conjecture in Reissner-Nordstr$\ddot{o}$m anti-de Sitter black holes are investigated by the scattering of the scalar field. The first law of thermodynamics in the non-extremal Reissner-Nordstr$\ddot{o}$m anti-de Sitter black hole is recovered by the scattering. The increase of the horizon radius indicates that the singularity is not naked in this black hole. For the near-extremal and extremal black holes, the validity is tested by the minimum values of the function $f$ at their final states. It is found that both of the near-extremal and extremal black holes can not be overcharged. When $ω=qϕ$, the final state of the extremal black hole is still an extremal black hole. When $ω\neq qϕ$, it becomes a near-extremal black hole with new mass and charge.

hep-th↗

arXiv2019

Thermodynamics and weak cosmic censorship conjecture in extended phase spaces of anti-de Sitter black holes with particles' absorption

The thermodynamics and weak cosmic censorship conjecture in extended phase spaces of charged anti-de Sitter black holes describing the massive gravity are investigated by the absorptions of the scalar particle and fermion. The cosmological constant is seen as a pressure with a conjugate volume. The first law of thermodynamics is recovered. The second law of thermodynamics is violated in the extended phase space of the extremal black hole. For the near-extremal and extremal black holes, the validity of weak cosmic censorship conjecture is tested by evaluating the minimum values of the metric function $f$. It is found that they remain their near-extremity and extremity when the particles are absorbed.

hep-th↗

arXiv2016

The modified first laws of thermodynamics of anti-de Sitter and de Sitter space-times

We modify the first laws of thermodynamics of a Reissner-Nordstrom anti-de Sitter black hole and a pure de Sitter space-time by the surface tensions. The corresponding Smarr relations are obeyed. The cosmological constants are first treated as fixed constants, and then as variables associated to the pressures. For the black hole, the law is written as $δE = T δS - σδA$ when the cosmological constant is fixed, where $E$ is the Misner-Sharp mass and $σ$ is the surface tension. Adopting the varied constant, we modify the law as $δE_0 = T δS - σ_{eff}δA +VδP$, where $E_0=M-\frac{Q^2}{2r_+}$ is the enthalpy. The thermodynamical properties are investigated. For the de Sitter space-time, the expressions of the modified laws are different from these of the black hole. The differential way to derive the law is discussed.

hep-th↗

arXiv2016

Modifying horizon thermodynamics by surface tensions

The modified first laws of thermodynamics at the black hole horizon and the cosmological horizon of the Schwarzschild de Sitter black hole and the apparent horizon of the Friedmann-Robertson-Walker cosmology are derived by the surface tensions, respectively. The corresponding Smarr relations are obeyed. For the black hole, the cosmological constant is first treated as a fixed constant, and then as a variable associated to the pressure. The law at the apparent horizon takes the same form as that at the cosmological horizon, but is different from that at the black hole horizon. The positive temperatures guarantee the appearance of the worked terms in the modified laws at the cosmological and apparent horizons. While they can disappear at the black hole horizon.

gr-qc↗

arXiv2014

Effects of quantum gravity on black holes

In this review, we discuss effects of quantum gravity on black hole physics. After a brief review of the origin of the minimal observable length from various quantum gravity theories, we present the tunneling method. To incorporate quantum gravity effects, we modify the Klein-Gordon equation and Dirac equation by the modified fundamental commutation relations. Then we use the modified equations to discuss the tunneling radiation of scalar particles and fermions. The corrected Hawking temperatures are related to the quantum numbers of the emitted particles. Quantum gravity corrections slow down the increase of the temperatures. The remnants are observed as $M_{\hbox{Res}}\gtrsim \frac{M_p}{\sqrt{β_0}}$. The mass is quantized by the modified Wheeler-DeWitt equation and is proportional to $n$ in quantum gravity regime. The thermodynamical property of the black hole is studied by the influence of quantum gravity effects.

gr-qc↗