When Primordial Black Holes Absorb During the Early Universe

TL;DR

This paper investigates how thermal absorption affects primordial black hole evolution, revealing significant mass growth and implications for dark matter and reheating, which alters previous understanding of PBH cosmological roles.

Contribution

It introduces the first comprehensive study of thermal absorption effects on PBHs, quantifying their impact on mass growth, lifetime, and cosmological parameters.

Findings

PBHs can undergo significant mass growth due to thermal absorption.

A critical collapse efficiency of approximately 0.395 determines unbounded mass growth.

Reheating temperature and dark matter parameter space are substantially affected.

Abstract

We study the evolution of primordial black holes (PBHs) formed in the early universe in the presence of a surrounding thermal bath. By incorporating the effects of thermal absorption, we show that PBHs can undergo significant mass growth, leading to extended lifetimes and substantial deviations from the standard Hawking evaporation scenario. We find a critical collapse efficiency, $\gamma_{\rm c} \simeq 0.395$, above which the PBH mass grows without bound. This correction has profound implications for both PBH-induced reheating and dark matter (DM) production. Specifically, we find that the reheating temperature can be suppressed, and the DM parameter space for the PBH reheating scenario can undergo $\mathcal{O}(10)$-$\mathcal{O}(10^4)$ corrections, depending on the PBH formation mass and collapse efficiency. Moreover, our results significantly shift the parameter space in which PBHs can account for the entirety of the DM. To the best of our knowledge, this is the first comprehensive phenomenological study to incorporate thermal absorption into PBH evolution and quantify its impact on cosmological observables.