  We investigate Primoridal Black Hole (PBH) formation by which we mean black
holes produced in the early universe during radiation domination. After
discussing the range of PBH mass permitted in the original mechanism of Carr
and Hawking, hybrid inflation with parametric resonance is presented as an
existence theorem for PBHs of arbitrary mass. As proposed in arXiv:1510.00400,
PBHs with many solar masses can provide a solution to the dark matter problem
in galaxies. PBHs can also explain dark matter observed in clusters and suggest
a primordial origin for supermassive black holes in galactic cores.
