Irreversible thermodynamics of Kerr-Newman black holes

The evaporation process of general Kerr-Newman black holes is discussed from a viewpoint of irreversible thermodynamics. The process is approximately regarded as a relaxation of a nonequilibrium Kerr-Newman state to its quasistationary counterpart, the Schwarzschild state with roughly the same mass. The thermodynamic fluctuations and evaporative evolution in the vicinity of the Schwarzschild limit are first discussed based, respectively, on the Kerr-Newman entropy expanded in the series of a small deviation from that limit and on the Langevin-type equations whose random-force terms reflect the effects of back reaction of evaporating particles. These equations are then generalized to describe the evaporation process of arbitrary Kerr-Newman holes and, by employing them, the validity of the fluctuation-dissipation theorem in the classical limit is demonstrated.