A new constraint on the Hawking evaporation of primordial black holes in the radiation-dominated era

TL;DR

This paper investigates the interplay of Hawking evaporation and accretion in primordial black holes during the radiation era, proposing a revised lower mass limit and challenging existing evaporation-based cosmological models.

Contribution

It introduces a new constraint on PBH evaporation by analyzing accretion effects, leading to a revised lower mass limit and questioning previous models of PBH evaporation in the early universe.

Findings

PBHs grow rapidly during the radiation era due to accretion

Hawking radiation becomes ineffective as PBHs' horizons expand

Lower mass limit for surviving PBHs is approximately 10^{14}g

Abstract

In this paper, we revisit the evaporation and accretion of primordial black holes (PBHs) during cosmic history and compare them to see if both of these processes are constantly active for PBHs or not. Our calculations indicate that during the radiation-dominated era, PBHs absorb ambient radiation due to accretion, and their apparent horizon grows rapidly. This growth causes the Hawking radiation process to practically fail and all the particles that escape as radiation from PBHs to fall back into them. Nevertheless, our emphasis is that the accretion efficiency factor also plays a very important role here and its exact determination is essential. We have shown that the lower mass limit for PBHs that have not yet evaporated should approximately be $10^{14}g$ rather than $10^{15}g$. Finally, we study the effects of Hawking radiation quiescence in cosmology and reject models based on the evaporation of PBHs in the radiation-dominated era.