New bounds on Memory Burdened Primordial Black Holes from Big Bang Nucleosynthesis

TL;DR

This paper revisits early-Universe constraints on ultralight primordial black holes, showing that quantum memory effects can significantly alter their evaporation dynamics and the resulting cosmological bounds from Big Bang Nucleosynthesis.

Contribution

It introduces the memory burden effect into the analysis of primordial black hole evaporation, providing revised bounds on ultralight PBHs in the early Universe.

Findings

Memory burden effect significantly alters previous PBH constraints.

New BBN-based bounds strongly limit ultralight PBHs with masses 1-100 g.

PBHs in the mass range 1-100 g are unconstrained by current observations.

Abstract

Primordial black holes (PBHs) with masses below $10^9\,\rm{g}$ are typically assumed to have negligible cosmological impact due to their rapid evaporation via Hawking radiation. However, the 'memory burden' effect, which is a quantum suppression of PBH evaporation, can dramatically alter their decay dynamics. In this work, we revisit early-Universe constraints on ultralight PBHs in this mass range, demonstrating that memory burden significantly alters previous constraints. We compute new cosmological bounds from BBN that strongly limit the presence of ultralight PBHs in the early Universe. We report that the PBHs in the mass range $10^0$-$10^2\,\rm{g}$ for $k=2$ are unconstrained by observations.