Primordial black holes from a cosmic phase transition: The collapse of Fermi-balls

Abstract: In this talk I will introduce a novel mechanism of forming primordial black holes (PBHs) via a first-order phase transition (FOPT). If a fermion species gains a huge mass in the true vacuum, the corresponding particles get trapped in the false vacuum as they do not have sufficient energy to penetrate the bubble wall. After the FOPT, the fermions are compressed into the false vacuum remnants to form non-topological solitons called Fermi-balls, and then collapse to PBHs due to the interior Yukawa attractive force. After describing the general mechanism, I will discuss a concrete application to the electroweak phase transition and demonstrate that a PBH dark matter scenario is possible.