# Primordial black holes from the preheating instability

## TL;DR

This paper investigates how resonant instabilities after inflation can lead to the formation of primordial black holes, which can dominate the universe's content and influence reheating, providing constraints on inflationary models.

## Contribution

It demonstrates that PBH formation during reheating is a generic outcome of simple inflationary models, without fine-tuning, and links PBH abundance to reheating temperature constraints.

## Key findings

- PBHs can dominate the universe after formation.
- Reheating temperature is tightly constrained by PBH abundance.
- PBH production is a generic feature of post-inflation dynamics.

## Abstract

After the end of inflation, the inflaton field oscillates around a local minimum of its potential and decays into ordinary matter. These oscillations trigger a resonant instability for cosmological perturbations with wavelengths that exit the Hubble radius close to the end of inflation. In this paper, we study the formation of Primordial Black Holes (PBHs) at these enhanced scales. We find that the production mechanism can be so efficient that PBHs subsequently dominate the content of the universe and reheating proceeds from their evaporation. Observational constraints on the PBH abundance also restrict the duration of the resonant instability phase, leading to tight limits on the reheating temperature that we derive. We conclude that the production of PBHs during reheating is a generic and inevitable property of the simplest inflationary models, and does not require any fine tuning of the inflationary potential.