Quasinormal modes and entropy spectrum of three dimensional Godel black hole

We have studied perturbations of scalar and spinor field in the background of three dimensional G\"{o}del black hole. The wave equations are shown to be exactly solvable in terms of hypergeometric functions. The quasinormal modes are analytically calculated by imposing the Dirichlet boundary condition at spatial infinity, which are shown to be of the same form in both cases. By considering the physical interpretation of quasinormal modes, we obtain the consistent transition frequencies from the quasinormal modes of scalar and spinor field. As an application of quasinormal modes, we have also investigated the area and entropy quantization of three dimensional G\"{o}del black hole. By choosing the conserved mass of G\"{o}del black hole properly, the entropy spectrum are shown to be equally-spaced.Comment: 18 pages, no figure

Stability of charged black holes in string theory under charged massive scalar perturbations

Similar to the superradiant effect in Reissner-Nordstr\"{o}m black hole, a charged scalar field can be amplified when impinging on the charged black hole in string theory. According to the black-hole bomb mechanism,the mass term of the incident field can works as the reflecting mirror, which may trigger the instability of black hole. We study the possible instability triggered by superradiant effect and demonstrate that the charged black hole in string theory is stable against the massive charged scalar perturbation. The reason is that there is no trapping potential well in the black hole exterior which is separated from the horizon by a potential barrier and there is no bound states in the superradiant regime.Comment: 12 pages, 3 figure

Superradiant instability of the charged scalar field in stringy black hole mirror system

It has been shown that the mass of the scalar field in the charged stringy black hole is never able to generate a potential well outside the event horizon to trap the superradiant modes. This is to say that the charged stringy black hole is stable against the massive charged scalar perturbation. In this paper we will study the superradiant instability of the massless scalar field in the background of charged stringy black hole due to a mirror-like boundary condition. The analytical expression of the unstable superradiant modes is derived by using the asymptotic matching method. It is also pointed out that the black hole mirror system becomes extremely unstable for a large charge $q$ of scalar field and the small mirror radius $r_m$.Comment: 5 pages, no figure, published versio

Hawking Radiation of Fermionic Field and Anomaly in 2+1 Dimensional Black Holes

The method of anomaly cancellation to derive Hawking radiation initiated by Robinson and Wilczek is applied to 2+1 dimensional stationary black holes. Using the dimensional reduction technique, we find that the near-horizon physics for the fermionic field in the background of the general 2+1 dimensional stationary black hole can be approximated by an infinite collection of two component fermionic fields in 1+1 dimensional spacetime background coupled with dilaton field and U(1) gauge field. By restoring the gauge invariance and the general coordinate covariance for the reduced two dimensional theory, Hawking flux and temperature of black hole are obtained. We apply this method to two types of black holes in three dimensional spacetime, which are BTZ black hole in Einstein gravity and a rotating black hole in Bergshoeff-Hohm-Townsend (BHT) massive gravity.Comment: 14pages, no figures, to appear in Class.Quant.Gra

Holographic description of three dimensional Godel black hole

Three dimensional G\"{o}del black hole is a solution to Einstein-Maxwell-Chern-Simons theory with a negative cosmological constant. We have studied the hidden conformal symmetry for massive scalar field without any additional condition in the background of three dimensional non-extremal and extremal G\"{o}del black holes. This conformal symmetry is uncovered by the observation that the radial wave equations in both cases can all be rewritten in the form of $SL(2, R)$ Casimir operators through introducing two sets of conformal coordinates to write the $SL(2, R)$ generators. At last, we give the holographic dual descriptions of Bekenstein-Hawking entropies of non-extremal and extremal black holes from Cardy formula of conformal field theory.Comment: 7 pages, no figur

Time evolutions of scalar field perturbations in DD-dimensional Reissner-Nordstr\"om Anti-de Sitter black holes

Reissner-Nordstr\"om Anti-de Sitter (RNAdS) black holes are unstable against the charged scalar field perturbations due to the well-known superradiance phenomenon. We present the time domain analysis of charged scalar field perturbations in the RNAdS black hole background in general dimensions. We show that the instabilities of charged scalar field can be explicitly illustrated from the time profiles of evolving scalar field. By using the Prony method to fit the time evolution data, we confirm the mode that dominates the long time behavior of scalar field is in accordance with the quasinormal mode from the frequency domain analysis. The superradiance origin of the instability can also be demonstrated by comparing the real part of the dominant mode with the superradiant condition of charged scalar field. It is shown that all the unstable modes are superradiant, which is consistent with the analytical result in the frequency domain analysis. Furthermore, we also confirm there exists the rapid exponential growing modes in the RNAdS case, which makes the RNAdS black hole a good test ground to investigate the nonlinear evolution of superradiant instability.Comment: 15 pages, 7 figure