Joint analysis of propagation-induced and PBH-induced gravitational-wave backgrounds

Develop a joint analysis of the propagation-induced and PBH-induced gravitational-wave contributions when the PBH-induced background is sufficiently large, or the pre-existing gravitational-wave background is sufficiently weak, to obscure the characteristic frequencies associated with the onset and end of the early matter-dominated era.

Background

The paper reconstructs an early primordial-black-hole-dominated era from two propagation-induced features in a stochastic gravitational-wave background: the frequency associated with the end of PBH domination and the frequency associated with its onset. This reconstruction assumes that gravitational waves induced by Poisson fluctuations in the PBH population remain subdominant and do not obscure those features.

For sufficiently large initial PBH abundances, or for a sufficiently small amplitude of the pre-existing gravitational-wave background, the PBH-induced contribution can instead become comparable to or larger than the propagation-induced signal. In that regime, the separate extraction of the two characteristic frequencies is no longer reliable, and the propagation-induced and PBH-induced components must be modeled simultaneously.