Constraining inflationary potentials with inflaton PBHs

If, after primordial inflation, the Universe undergoes a relatively long reheating period, it could present a phase of matter domination supported by the oscillating inflaton field. During this epoch, small perturbations from the inflaton that reenter the cosmological horizon could virialize to form inflaton structures. If the primordial overdensities are large enough, their associated inflaton structures could collapse to form primordial black holes (PBHs) [L. E. Padilla et al., New mechanism for primordial black hole formation during reheating, Phys. Rev. D 106, 023519 (2022); hereinafter P1.]. For this to happen at a considerable rate, the primordial power spectrum should be enhanced at small scales, a feature typically induced in single-field inflation through an ultraslow roll phase (produced by a nearly inflection point in the inflationary potential). In this paper we consider two specific inflationary potentials that present this nearly inflection point, and we look at the PBH formation rate through the mechanism proposed in P1. We report on constraints to these two specific models from the bounds to PBH abundances. This serves as an illustration of the usefulness of the PBH formation mechanism proposed in P1.