Speaker
Description
In this talk, I will discuss how primordial black holes (PBHs) and their associated stochastic gravitational-wave backgrounds can probe the post-inflationary Universe. I will first consider PBH formation during a non-standard reheating phase, where an enhanced primordial scalar power spectrum can simultaneously generate PBHs and scalar-induced gravitational waves. Accounting for uncertainties in PBH formation and current abundance constraints, I will show that a reheating phase with an equation of state stiffer than radiation can produce a gravitational-wave spectrum consistent with the NANOGrav 15-year data, with stronger Bayesian evidence than the supermassive black-hole binary scenario in suitable regions of parameter space. I will then discuss a complementary scenario in which PBHs dominate the Universe before evaporating through Hawking radiation, generating induced gravitational waves from both PBH isocurvature perturbations and enhanced adiabatic perturbations during the transition to radiation domination. Using signal-to-noise estimates and Fisher forecast analyses, I will present the prospects for detecting these signals with LISA and the Einstein Telescope. Together, these scenarios demonstrate how gravitational-wave observations from PTA to interferometer frequencies can constrain PBH formation mass, abundance, and the early-Universe equation of state, providing a multi-frequency probe of reheating.
References: JCAP 01 (2025) 118; JCAP 08 (2025) 074.