Primordial black hole formation from self-resonant preheating?

TL;DR

This paper investigates the likelihood of primordial black hole formation during preheating after inflation, finding it to be non-generic and often overshadowed by oscillon formation due to anharmonic effects.

Contribution

The study combines analytical and lattice methods to assess the role of self-resonant inflaton fluctuations in primordial black hole production, highlighting the importance of anharmonicity.

Findings

Black hole formation is not a common outcome in self-resonant preheating.

Anharmonic potential effects lead to oscillon formation rather than black holes.

Metric preheating terms are often subdominant in viable inflation models.

Abstract

We revisit the question of how generic is the formation of primordial black holes via self-resonant growth of inflaton fluctuations in the post-inflationary, preheating phase. Using analytical and lattice calculations, we find that primordial black hole production is far from being a generic outcome. Also, in most of the parameter space of viable inflationary models, the metric preheating term is subleading to the anharmonic terms and the approximation of a quadratic potential for describing the resonance dynamics is inadequate. Nonetheless, the anharmonicity of the potential cannot be used to rescue the mechanism: The generic outcome of the non-linear evolution of the scalar field in this case is the formation of metastable transients or oscillons, that do not generically collapse into black holes.