Speaker
Description
Primordial curvature perturbations seed both primordial black holes (PBHs) and scalar-induced gravitational waves (SIGWs). However, the standard second-order perturbative calculation of SIGWs omit important nonlinear effect. Once these perturbations re-enter the horizon, their gravitational collapse and subsequent nonlinear hydrodynamic evolution excite strong sound waves in the primordial plasma. Collisions among these sound waves constitute a distinct and additional source of gravitational waves. Here we employ the Misner-Sharp formalism to derive the initial fluid profiles of a single sound wave produced by the gravitational collapse of an overdensity. Building on these profiles, we adapt the sound shell model and perform three-dimensional lattice simulations to compute the gravitational-wave signal produced by an ensemble of such sound waves. These acoustic gravitational waves are complementary to conventional SIGWs and offer a new observational target for future gravitational-wave detectors.
