Non-oscillatory gravitational quasinormal modes of Reissner-Nordström-de Sitter spacetime

Abstract: Proper oscillation frequencies of black holes (quasinormal modes) of asymptotically de Sitter black holes were extensively studied, yet the non-oscillatory (purely imaginary) branch of modes of gravitational perturbations of the four-dimensional Reissner-Nordstr\"om-de Sitter solution was omitted in the literature. This branch of modes appears as deformations of the modes of empty de Sitter space. Here we find accurate numerical values of this branch of quasinormal modes and show that they are responsible for the exponential asymptotic tails.