Radiation from a scalar charge in Schwarzschild-de Sitter spacetimes

Abstract

The Schwarzschild-de Sitter (SdS) spacetime is a simple model for a black hole immersed in a universe
with a positive cosmological constant. We calculate the radiation generated by a scalar charged
particle moving in this spacetime, with the goal of understanding its dependence on the cosmological
constant Λ. We take interest in a particle undergoing circular geodesic motion, which is specified by a
unique orbital frequency at each orbital radius. We compute the energy flux spectra of the radiation
crossing both horizons. We determine that most of the power comes from the lower modes of the
scalar wave and that the contribution of the higher modes exponentially decreases with increasing
mode number. Our results show that the energy flux has little dependence on Λ.