The evolution of primordial black hole masses in the radiation- dominated era

TL;DR

This paper analyzes the mass evolution of primordial black holes during the radiation era, showing they gain negligible mass and cannot stay in thermal equilibrium, which supports observational searches for evaporating black holes.

Contribution

It provides a complete differential equation solution for PBH mass evolution considering absorption and evaporation, clarifying their growth limitations in the radiation era.

Findings

PBHs gain very little mass in the radiation era

Relativistic motion does not significantly affect PBH growth

PBHs cannot remain in thermal equilibrium with radiation

Abstract

We revisit the problem of PBH mass evolution in the radiation-dominated era. We solve the complete differential equation in the semiclassical regime with absorption and evaporation terms and show that PBHs can gain very little mass, if at all, in this era. Relativistic proper motion of PBHs respect to the CMBR, as a possible loophole in the growth argument, is shown to be unlikely. Finally we demonstrate that PBHs can not remain in thermodynamical equilibrium with the ambient radiation, and therefore initially non-evaporating black holes must enter the evaporating regime, supporting several efforts to look for observational signatures.