Resilience of Primordial Black Hole Formation from Inflation with a Light Spectator Field

Abstract

Scalar fields are ubiquitous in theories of high-energy physics. In the context of cosmic inflation, this suggests the existence of spectator fields, which provide a subdominant source of energy density. We show that spectator fields boost the inflationary production of primordial black holes, with single-field ultra-slow-roll evolution supplanted by a phase of evolution along the spectator direction, and primordial perturbations amplified by the resulting multifield dynamics. This generic mechanism is largely free from the severe fine-tuning that afflicts single-field inflationary PBH models.

arXiv comment5 pages, 4 figures + supplemental material. v2: matches version published in PRD. PBHspec code publicly available at: https://github.com/dario-lorenzoni/PBHspec