Complex Scalar Field Reheating and Primordial Black Hole production

TL;DR

This paper investigates how perturbations in a complex scalar field during reheating can lead to the formation of primordial black holes, with implications for dark matter relics and differences from real scalar field behavior.

Contribution

It provides a detailed analysis of instability scales and PBH production in complex scalar fields during reheating, highlighting differences from real scalar fields and implications for dark matter.

Findings

Identified a distinct instability scale for complex scalar fields.

Found significant production of tiny primordial black holes that evaporate quickly.

Imposed constraints on reheating parameters based on relic dark matter considerations.

Abstract

We study perturbations of a complex scalar field during reheating with no self-interaction in the regime $ \mu \gg H$, when the scalar field has a fast oscillatory behaviour (close to a pressure-less fluid). We focus on the precise determination of the instability scale and find it differs from that associated with a real scalar field. We further look at the probability that unstable fluctuations form Primordial Black Holes (PBHs) obtaining a significant production of tiny PBHs which quickly evaporate and may subsequently leave a population of Planck-mass relics. We finally impose restrictions on the duration and energy scale of the fast oscillations period by considering that such relics constitute, at most, the totality of dark matter in the Universe.