Physics Seminar

 

Abstract: "First-order phase transitions in an early universe can generate gravitational waves (GWs) and produce primordial black holes (PBHs). In this talk, I will discuss a mechanism in which false-vacuum domains left behind by the transition undergo gravitational collapse as they shrink. Unlike conventional PBH formation scenarios based on large density perturbations or overdensity thresholds, this collapse is driven by the vacuum energy contained within the domains. We describe the collapse dynamics using a junction-condition formalism and study the resulting PBH and GW signals in classically conformal particle models. We identify regions of parameter space that produce observable GWs, observable PBHs, or both, providing complementary probes of the underlying particle physics. In particular, transitions occurring on energy scales in the range 1–100 MeV are found to offer strong GW signals while potentially providing all of the observed dark matter in the form of PBHs.”