Radiation processes in the vicinity of non-Schwarzschild and non-Kerr   black holes
  Usually alternative theories of gravity imply deviations from the well-known Kerr space-time, a model of an isolated black hole in General Relativity. In the dominant order, the deformed Kerr metric, free of closed time-like curves outside the event horizon, has been suggested recently by Johannsen and Psaltis. It has a single deformation parameter which is not constrained by the current observations, allowing, thereby, for a kind of unified and simple phenomenological description of black holes in various theories of gravity. Here we consider a number of classical and quantum phenomena of radiation in the vicinity of such deformed Schwarzschild-like and Kerr-like black holes: spiralling of particles into black holes, decay of fields propagating in the black hole's background, Hawking radiation. In particular, we calculate some quantitative characteristics of the above phenomena, such as the binding energy of particles, quasinormal modes, late-time tails of fields of various spin, intensity of Hawking radiation. The binding energy released when a particle goes over from a given stable orbit in the equatorial plane to the innermost stable one is calculated for such non-Kerr black holes. Due to inseparability of the wave equations in the general case, the perturbations and stability of scalar, Dirac, and electromagnetic fields are analyzed for vanishing rotation only. The dependence of the radiation phenomena on the deformation parameter is discussed. 
R. A. Konoplya, A. Zhidenko
gr-qc astro-ph.HE hep-th