Primordial Black Hole Formation During Slow Reheating After Inflation

TL;DR

This paper investigates how primordial black holes form during slow reheating after inflation, revealing a threshold for density fluctuations and a maximum mass cutoff relevant to LIGO black hole observations.

Contribution

It introduces a new analysis of PBH formation during slow reheating, including a threshold for density contrast and a maximum PBH mass cutoff, impacting observational predictions.

Findings

Threshold for density contrast variance: σ_c ≈ 0.05

Maximum PBH mass around 100 solar masses

Implications for LIGO black hole merger observations

Abstract

We study the formation of primordial black holes (PBHs) in the early Universe during a period of slow reheating after inflation. We demonstrate how the PBH formation mechanism may change even before the end of the matter-dominated phase and calculate the expected PBH mass function. We find that there is a threshold for the variance of the density contrast, $\sigma_c \simeq 0.05$, below which the transition occurs even before reheating, with this having important consequences for the PBH mass function. We also show that there is a maximum cut-off for the PBH mass at around $100\,M_{\odot}$, below which the subdominant radiation bath affects PBH production, making the scenario particularly interesting for the recent LIGO observations of black hole mergers.