scholarly journals Geodesic stability and quasi normal modes via Lyapunov exponent for Hayward black hole

2020 ◽  
Vol 35 (30) ◽  
pp. 2050249
Author(s):  
Monimala Mondal ◽  
Parthapratim Pradhan ◽  
Farook Rahaman ◽  
Indrani Karar
Keyword(s):  
Black Hole ◽  
Lyapunov Exponent ◽  
Time Scale ◽  
Proper Time ◽  
Normal Modes ◽  
Schwarzschild Black Hole ◽  
Coordinate Time ◽  
Stability And Instability ◽  
The Stability ◽  
Asymptotic Observers

We derive proper time Lyapunov exponent [Formula: see text] and coordinate time Lyapunov exponent [Formula: see text] for a regular Hayward class of black hole. The proper time corresponds to [Formula: see text] and the coordinate time corresponds to [Formula: see text], where [Formula: see text] is measured by the asymptotic observers both for Hayward black hole and for special case of Schwarzschild black hole. We compute their ratio as [Formula: see text] for time-like geodesics. In the limit of [Formula: see text] that means for Schwarzschild black hole this ratio reduces to [Formula: see text]. Using Lyapunov exponent, we investigate the stability and instability of equatorial circular geodesics. By evaluating the Lyapunov exponent, which is the inverse of the instability time scale, we show that, in the eikonal limit, the real and imaginary parts of quasi-normal modes (QNMs) is specified by the frequency and instability time scale of the null circular geodesics. Furthermore, we discuss the unstable photon sphere and radius of shadow for this class of black hole.

scholarly journals Stability analysis of circular orbits around a charged BTZ black hole spacetime in a nonlinear electrodynamics model via Lyapunov exponents

2021 ◽  
Author(s):  
Shobhit Giri ◽  
Hemwati Nandan ◽  
Lokesh Kumar Joshi ◽  
Sunil D. Maharaj
Keyword(s):  
Black Hole ◽  
Stability Analysis ◽  
Lyapunov Exponent ◽  
Cosmological Constant ◽  
Proper Time ◽  
Btz Black Hole ◽  
Circular Orbits ◽  
Coordinate Time ◽  
Conformally Invariant ◽  
The Stability

We investigate the existence and stability of both the timelike and null circular orbits for a (2 + 1)-dimensional charged BTZ black hole in Einstein-nonlinear Maxwell gravity with a negative cosmological constant. The stability analysis of orbits is performed to study the possibility of chaos in geodesic motion for a special case of black hole so-called conformally invariant Maxwell spacetime. The computations of both proper time Lyapunov exponent [Formula: see text] and coordinate time Lyapunov exponent [Formula: see text] are useful to determine the stability of these circular orbits. We observe the behavior of the ratio [Formula: see text] as a function of radius of circular orbits for the timelike case in view of different values of charge parameter. However, for the null case, we calculate only the coordinate time Lyapunov exponent [Formula: see text] as there is no proper time for massless test particles. More specifically, we further analyze the behavior of the ratio of [Formula: see text] to angular frequency [Formula: see text], so-called instability exponent as a function of charge [Formula: see text] and parameter related to cosmological constant [Formula: see text] for the particular values of other parameters.

scholarly journals Radial and circular motion of photons and test particles in the Schwarzschild black hole with quintessence and string clouds

2021 ◽  
Vol 81 (5) ◽  
Author(s):  
G. Mustafa ◽  
Ibrar Hussain
Keyword(s):  
Black Hole ◽  
Proper Time ◽  
Schwarzschild Black Hole ◽  
Circular Orbits ◽  
Coordinate Time ◽  
Test Particles ◽  
Close Proximity ◽  
Massive Particles ◽  
Quintessence Field ◽  
Cloud Parameter

AbstractThe null and timelike geodesic motion in the vicinity of the Schwarzschild black hole in the presence of the string cloud parameter a and the quintessence field parameter q is studied. The ranges for both the parameters a and q are determined, which allow the existence of the black hole. In the radial motion of photon, the coordinate time t first decreases with the increasing values of both the parameters a and q and then in the close proximity of the horizon of the black hole, there is a turning point, after which the effect of the quintessence field is just opposite on the time t. For the massive particles, the proper time $$\tau $$ τ decreases with increasing values of the parameter a and increases with increase in the value of the parameter q. In the same case of the massive particles, the coordinate time t decreases with increase in the values of both the parameters a and q. Further, it is found that for test particles, the stable circular orbits exist in this spacetime for small values of both the parameters i.e., for $$0<a\ll 1$$ 0 < a ≪ 1 and $$0<q\ll 1$$ 0 < q ≪ 1 . It is observed that the radii of the null circular orbits increase as the values of the parameters a and q increase. While in the case of the timelike geodesics, the radii of the circular orbits increase as the value of the parameter a increases, and they decrease as the value of the parameter q increases.

scholarly journals Black hole S-matrix for a scalar field

2021 ◽  
Vol 2021 (7) ◽  
Author(s):  
Panos Betzios ◽  
Nava Gaddam ◽  
Olga Papadoulaki
Keyword(s):  
Black Hole ◽  
Normal Modes ◽  
Massless Scalar ◽  
Scattering Process ◽  
Schwarzschild Black Hole ◽  
Asymptotically Flat ◽  
Scalar Particles ◽  
Black Hole Background ◽  
S Matrix ◽  
Do So

Abstract We describe a unitary scattering process, as observed from spatial infinity, of massless scalar particles on an asymptotically flat Schwarzschild black hole background. In order to do so, we split the problem in two different regimes governing the dynamics of the scattering process. The first describes the evolution of the modes in the region away from the horizon and can be analysed in terms of the effective Regge-Wheeler potential. In the near horizon region, where the Regge-Wheeler potential becomes insignificant, the WKB geometric optics approximation of Hawking’s is replaced by the near-horizon gravitational scattering matrix that captures non-perturbative soft graviton exchanges near the horizon. We perform an appropriate matching for the scattering solutions of these two dynamical problems and compute the resulting Bogoliubov relations, that combines both dynamics. This allows us to formulate an S-matrix for the scattering process that is manifestly unitary. We discuss the analogue of the (quasi)-normal modes in this setup and the emergence of gravitational echoes that follow an original burst of radiation as the excited black hole relaxes to equilibrium.

Gravitational analysis of neutral regular black hole in Rastall gravity

2020 ◽  
Vol 35 (27) ◽  
pp. 2050225 ◽  
Author(s):  
Riasat Ali ◽  
Muhammad Asgher ◽  
M. F. Malik
Keyword(s):  
Black Hole ◽  
Wave Equation ◽  
Quantum Gravity ◽  
Generalized Uncertainty Principle ◽  
Gravity Effect ◽  
Tunneling Radiation ◽  
Regular Black Hole ◽  
Quantum Gravity Effect ◽  
Stability And Instability ◽  
The Stability

This paper is devoted to the tunneling radiation and quantum gravity effect on tunneling radiation of neutral regular black hole in Rastall gravity. We analyzed the tunneling radiation and Hawking temperature of neutral regular black hole by applying the Hamilton-Jacobi ansatz phenomenon. Lagrangian wave equation have been investigated by generalized uncertainty principle (GUP), using the WKB-approximation and calculated the tunneling rate as well as temperature. Furthermore, we analyzed the temperature of this neutral regular black hole in the presence of gravity. The stability and instability of neutral regular black hole are also analyzed.

scholarly journals QUASI-NORMAL MODES OF SCHWARZSCHILD–ANTI-DE SITTER BLACK HOLES: ELECTROMAGNETIC AND GRAVITATIONAL PERTURBATIONS

2002 ◽  
Vol 17 (20) ◽  
pp. 2752-2752
Author(s):  
VITOR CARDOSO ◽  
JOSÉ P. S. LEMOS
Keyword(s):  
Black Hole ◽  
Imaginary Part ◽  
Normal Modes ◽  
De Sitter ◽  
Schwarzschild Black Hole ◽  
Small Black Hole ◽  
Conformal Field ◽  
Gravitational Perturbations ◽  
Ads Spacetime ◽  
Electromagnetic Perturbation

We studied the quasi-normal modes (QNM) of electromagnetic and gravitational perturbations of a Schwarzschild black hole in an asymptotically anti-de Sitter (AdS) spacetime, extending previous works1,2 on the subject. Some of the electromagnetic modes do not oscillate, they only decay, since they have pure imaginary frequencies. The gravitational modes show peculiar features: the odd and even gravitational perturbations no longer have the same characteristic quasinormal frequencies. There is a special mode for odd perturbations whose behavior differs completely from the usual one in scalar1 and electromagnetic perturbation in an AdS spacetime, but has a similar behavior to the Schwarzschild black hole3 in an asymptotically flat spacetime: the imaginary part of the frequency goes as [Formula: see text], where r+ is the horizon radius. We also investigated the small black hole limit showing that the imaginary part of the frequency goes as [Formula: see text]. These results are important to the AdS/CFT4 conjecture since according to it the QNMs describe the approach to equilibrium in the conformal field theory. For other geometries see5,6.

scholarly journals NUMERICAL SIMULATION OF QUASI-NORMAL MODES IN TIME-DEPENDENT BACKGROUND

2004 ◽  
Vol 19 (03) ◽  
pp. 239-252 ◽  
Author(s):  
LI-HUI XUE ◽  
ZAI-XIONG SHEN ◽  
BIN WANG ◽  
RU-KENG SU
Keyword(s):  
Numerical Simulation ◽  
Black Hole ◽  
Wave Propagation ◽  
Normal Modes ◽  
Time Dependent ◽  
Massless Scalar ◽  
Scalar Wave ◽  
Schwarzschild Black Hole ◽  
Black Hole Background ◽  
Scattering Potential

We study the massless scalar wave propagation in the time-dependent Schwarzschild black hole background. We find that the Kruskal coordinate is an appropriate framework to investigate the time-dependent spacetime. A time-dependent scattering potential is derived by considering dynamical black hole with parameters changing with time. It is shown that in the quasinormal ringing both the decay time-scale and oscillation are modified in the time-dependent background.

Black hole spectroscopy from a class of Plebański and Demiański space–times

2014 ◽  
Vol 92 (1) ◽  
pp. 46-50
Author(s):  
De-Jiang Qi
Keyword(s):  
Black Hole ◽  
Normal Modes ◽  
Kerr Black Hole ◽  
Black Hole Thermodynamics ◽  
Area Spectrum ◽  
Spherically Symmetric ◽  
Adiabatic Invariance ◽  
Schwarzschild Black Hole ◽  
Gravity System ◽  
Area Spectra

Recently, via adiabatic invariance, Majhi and Vagenas quantized the horizon area of the general class of a static spherically symmetric space–time. Very recently, applying the period of the gravity system with respect to the Euclidean time, Zeng and Liu derived area spectra of a Schwarzschild black hole and a Kerr black hole. It is noteworthy that the preceding methods are not useful for the quasi-normal modes. In this paper, based on those works, and as a further study, adopting near horizon approximation, applying the laws of black hole thermodynamics, we would like to investigate the black hole spectroscopy from a class of Plebański and Demiański space–times by using two different methods. The result shows that the area spectrum of the black hole is [Formula: see text], which confirms the initial proposal of Bekenstein, and the result is consistent with that already obtained by Maggiore with quasi-normal modes.

scholarly journals Effective GUP-modified Raychaudhuri equation and black hole singularity: four models

2021 ◽  
Vol 2021 (9) ◽  
Author(s):  
Keagan Blanchette ◽  
Saurya Das ◽  
Saeed Rastgoo
Keyword(s):  
Black Hole ◽  
Proper Time ◽  
Generalized Uncertainty Principle ◽  
Rate Of Change ◽  
Conjugate Points ◽  
Raychaudhuri Equation ◽  
Schwarzschild Black Hole ◽  
Effective Dynamics ◽  
Singularity Theorems ◽  
Black Hole Singularity

Abstract The classical Raychaudhuri equation predicts the formation of conjugate points for a congruence of geodesics, in a finite proper time. This in conjunction with the Hawking-Penrose singularity theorems predicts the incompleteness of geodesics and thereby the singular nature of practically all spacetimes. We compute the generic corrections to the Raychaudhuri equation in the interior of a Schwarzschild black hole, arising from modifications to the algebra inspired by the generalized uncertainty principle (GUP) theories. Then we study four specific models of GUP, compute their effective dynamics as well as their expansion and its rate of change using the Raychaudhuri equation. We show that the modification from GUP in two of these models, where such modifications are dependent of the configuration variables, lead to finite Kretchmann scalar, expansion and its rate, hence implying the resolution of the singularity. However, the other two models for which the modifications depend on the momenta still retain their singularities even in the effective regime.

Effects of electromagnetic field on the motion of particles in dyonic Reissner–Nordström black hole

2017 ◽  
Vol 26 (09) ◽  
pp. 1750091 ◽  
Author(s):  
M. Sharif ◽  
Sehrish Iftikhar
Keyword(s):  
Black Hole ◽  
Electromagnetic Field ◽  
Lyapunov Exponent ◽  
Circular Orbit ◽  
Center Of Mass ◽  
Mass Energy ◽  
Center Of Mass Energy ◽  
Stable Circular Orbit ◽  
The Stability ◽  
Dynamics Of Particles

This paper explores dynamics of particles in the combined gravitational and electromagnetic fields of the dyonic Reissner–Nordström background. We discuss possibilities for the particle escape to infinity at inner most stable circular orbit. We study the stability of orbit through Lyapunov exponent and the effective force on particle. The collision of particles is investigated through the center of mass energy near the horizon of black hole. Finally, we compare our results with the motion of particles around Schwarzschild and Reissner–Nordström black hole. We conclude that charge of the black hole has a strong effect on the motion of particles.

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