Recent work in the theory of black holes

Perturbations in the Kerr-Newman Dilatonic Black Hole Background: Maxwell Waves
R. Casadio, B. Harms, Y. Leblanc and P.H. Cox
Phys. Rev. D56, 4948(1997)


In this paper we analyze the perturbations of the Kerr-Newman dilatonic black hole background. For this purpose we perfom a double expansion in both the background electric charge and the wave parameters of the relevant quantities in the Newman-Penrose formalism. We then display the gravitational, dilatonic and electromagnetic equations, which reproduce the static solution (at zero order in the wave parameter) and the corresponding wave equations in the Kerr background (at first order in the wave parameter and zero order in the electric charge). At higher orders in the electric charge one encounters corrections to the propagation of waves induced by the presence of a non-vanishing dilaton. An explicit computation is carried out for the electromagnetic waves up to the asymptotic form of the Maxwell field perturbations produced by the interaction with dilatonic waves. A simple physical model is proposed which could make these perturbation relevant in the detection of radiation coming from the region of space near a black hole.


Statistical mechanics of Kerr-Newman dilaton black holes and the bootstrap condition
R. Casadio, B. Harms and Y. Leblanc
Phys. Rev. D57, 1309(1998)


The Bekenstein-Hawking entropy of a Kerr-Newman dilaton black hole is computed in a perturbative expansion in the charge-to-mass ratio. The most probable configuration for a gas of such black holes is analyzed in the microcanonical formalism and it is argued that it does not satisfy the equipartition principle but does satisfy a bootstrap condition.


Perturbation in the Kerr-Newman Dilatonic Black Hole Background: Maxwell Waves, the Dilaton Background and Gravitational Lensing
R. Casadio and B. Harms
Phys. Rev. D 58, 044015(1998)


In this paper we continue the analysis of one of our previous papers and study the affect of the existence of a non-trivial dilaton background on the propagation of electromagnetic waves in the Kerr-Newman dilatonic black hole space-time. For this purpose we again employ the double expansion in both the background electric charge and the wave parameters of the relevant quantities in the Newman-Penrose formalism and then identify the first order at which the dilaton background enters Maxwell equations. We then assume that gravitational and dilatonic waves are negligible (at that order in the charge parameter) with respect to electromagnetic waves and argue that this condition is consistent with the solutions already found in the previous paper. Explicit expressions are given for the asymptotic behaviour of scattered waves, and a simple physical model is proposed in order to test the effects. An expression for the relative intensity is obtained for Reissner-Nordström dilaton black holes using geometrical optics. A comparison with the approximation of geometrical optics for Kerr-Newman dilaton black holes shows that at the order to which the calculations are carried out gravitational lensing of optical images cannot probe the dilaton background.


Microfield Dynamics of Black Holes
R. Casadio and B. Harms
Phys. Rev. D58, 044014(1998)


The microcanonical treatment of black holes as opposed to the canonical formulation is reviewed and some major differences are displayed. In particular the decay rates are compared in the two different pictures.