Speaker
Description
I will discuss the scattering problem for a massless scalar field in a Schwarzschild-de Sitter geometry. A rigorous application of the method of matched asymptotic expansions allows us to solve analytically the low-frequency s-wave dynamics, and connect the scalar’s evolution in the proximity of the black-hole horizon with that on cosmological scales. The scattering coefficients, greybody factors, and Wigner time delay are computed explicitly. We consider both small and large black holes (relative to the cosmological horizon), extending previous studies confined to the small black-hole regime. In addition, for small black holes we perform a calculation that remains agnostic about the relative size between the ratio of the geometry’s horizons and the scalar’s frequency in units of the black-hole radius. When the two are comparable, we find that the greybody factor is symmetric under the exchange of the scalar frequency and the cosmological horizon radius.
Based on arxiv:2511.09168 (to appear in PRD), in collaboration with M. Miranda and A.P. Porfyriadis.