Relativistic accretion and burdened primordial black holes

TL;DR

This paper explores how relativistic accretion and memory burdened evaporation influence primordial black hole evolution, potentially allowing small PBHs to survive until today and contribute to dark matter and radiation.

Contribution

It introduces the combined effects of relativistic accretion and memory burdened evaporation on PBH evolution, revealing new survival scenarios and observational implications.

Findings

Memory burden delays PBH evaporation, enabling survival of PBHs with mass less than 10^{15} g.

Accretion enhances PBH mass, increasing their survival probability and dark matter contribution.

Evaporation emits dark matter and dark radiation, affecting cosmological parameters.

Abstract

We examine the joint effects of relativistic accretion and memory burdened evaporation on the evolution of primordial black holes (PBHs). The memory burden effect, which delays the evaporation by inducing a backreaction and making the evaporation rate scale as an inverse power law of the PBH entropy, opens up a new window that allows PBHs with $M \lesssim 10^{15}~\mathrm{g}$ to survive until the present epoch. Meanwhile, accretion increases the mass of PBHs, thereby enhancing their chances of survival for a given initial mass. We consider two main scenarios: one where PBHs evaporate completely before big bang nucleosynthesis, and another where PBHs persist until today. In the case of evaporation, we analyse the emission of dark matter (DM) and dark radiation (DR) during the process of evaporation. Conversely, in the other case, the surviving PBHs themselves can contribute as DM. We further investigate how relativistic and non-relativistic accretion, together with memory burdened evaporation, impact the parameter space of the emitted DM, the abundance of stable PBHs as DM, and the contribution of DR to the effective number of relativistic degrees of freedom, $\Delta N_{\mathrm{eff}}$.