Reheating in runaway inflation models via the evaporation of mini primordial black holes

TL;DR

This paper explores how mini primordial black holes formed during a stiff fluid phase can reheat the universe through evaporation, potentially leaving remnants and contributing to dark energy, with observable gravitational wave signatures.

Contribution

It introduces a scenario where mini PBHs from a runaway inflation model reheat the universe and predicts unique gravitational wave signals, expanding understanding of early universe cosmology.

Findings

Mini PBHs evaporate promptly, reheating the early universe.

A gravitational wave signal with distinct features is predicted.

Residual PBH remnants could exist in galaxies.

Abstract

We investigate the cosmology of mini Primordial Black Holes (PBHs) produced by large density perturbations that collapse during a stiff fluid domination phase. Such a phase can be realized by a runaway-inflaton model that crosses an inflection point or a sharp feature at the last stage of inflation. Mini PBHs evaporate promptly and reheat the early universe. In addition, we examine two notable implications of this scenario: the possible presence of PBH evaporation remnants in galaxies and a non-zero residual potential energy density for the runaway inflaton that might play the role of the dark energy. We specify the parameter space that this scenario can be realized and we find that a transit PBH domination phase is necessary due to gravitational wave (GW) constraints. A distinct prediction of the scenario is a compound GW signal that might be probed by current and future experiments. We also demonstrate our results employing an explicit inflation model.