Title: Formation of primordial black holes during the QCD phase transition
Abstract: The formation of Primordial black holes is naturally enhanced during the quark-hadron phase transition, because of the softening of the equation of state occurring during this epoch: at a scale between 1 and 3 solar masses, the threshold is reduced of about 10% with a corresponding abundance of primordial black holes significantly increased by more than 100 times. We show that a sub-population of primordial black black holes formed during the QCD epoch, in the solar mass range, is compatible with the current observational constraints, and could explain some of the interesting sources emitting gravitational waves detected by LIGO/VIRGO in the black hole mass gap, such as GW190814, and other light events.