ar X iv : g r - qc / 9 70 50 86 v 1 3 0 M ay 1 99 7 UAHEP 976 Perturbations in the Kerr - Newman Dilatonic Black Hole

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 gravita-tional, 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.