Correspondence between quasinormal modes and grey-body factors for massive fields in Schwarzschild-de Sitter spacetime

Recently, a correspondence between quasinormal modes and grey-body factors of black holes has been established. This correspondence is known to be exact in the eikonal regime for a large class of asymptotically flat black holes and approximate when the multipole number $\ell$ is small. In this work, we demonstrate that there exists a regime where the correspondence holds with unprecedented accuracy even for the lowest multipole numbers: specifically, for perturbations of massive fields in the background of asymptotically de Sitter black holes, provided the field mass is not very small. We also fill the gap in the existing literature via finding the grey-body factors of a massive scalar field in the Schwarzschild- de Sitter background, when $\mu M/m_{P}$ is not small.