Speaker
Description
We investigate the scalar-induced gravitational wave (SIGW) signal originating from the evaporation of primordial black holes (PBHs). In the idealized monochromatic mass scenario, a pronounced SIGW signal arises via the so-called poltergeist mechanism, triggered by a sharp transition from matter to radiation domination. However, more realistic extended mass distributions—such as those predicted by the Press–Schechter formalism and peak theory for PBHs formed from the collapse of superhorizon overdensities—smooth this transition.
Using both Press–Schechter and peak theory, we derive the narrowest extended mass function consistent with superhorizon collapse. We show that even in this limiting case, the associated smoothing leads to a significant suppression of the resulting GW signal. This suppression limits the detectability of large parts of the ultra-light PBH parameter space by future GW observatories, while simultaneously relaxing stringent Big Bang nucleosynthesis (BBN) bounds and reopening previously excluded regions.
Our analysis carefully treats the curvature power spectrum cutoff and consistently includes contributions from both adiabatic and isocurvature initial conditions. In particular, we revisit and update the transfer functions and the evolution of adiabatic and isocurvature fluctuations across the radiation-dominated to early matter-dominated transition.
Furthermore, we extend our framework to SIGWs generated during early matter- and radiation-dominated phases, including enhancements of the power spectrum at PBH formation. Separately, we analyze the high-frequency gravitational wave contribution from PBH binaries, accounting for different merger channels, as well as from PBH evaporation.