Opening the Window of Ultra-Light PBHs by Exorcising the Poltergeist

TL;DR

This paper challenges standard predictions about primordial black hole evaporation, showing that considering the mass distribution tail smooths reheating and significantly reduces gravitational wave signals, reopening the possibility of ultra-light PBHs.

Contribution

It introduces the impact of the general relativity predicted mass tail on PBH evaporation, altering previous expectations and expanding the viable parameter space for ultra-light PBHs.

Findings

Reheating is smoothed by the mass tail, reducing abruptness.

Gravitational wave signals are suppressed by orders of magnitude.

The ultra-light PBH window is reopened due to these effects.

Abstract

The hot Big Bang may have emerged from evaporation of primordial black holes (PBHs) lighter than $10^9$g. Standard monochromatic treatments predict nearly simultaneous evaporation, abrupt reheating, and a large Poltergeist scalar-induced gravitational wave signal. We confront this expectation with the irreducible collapse mass tail predicted by general relativity, $df_{\rm PBH}/d\ln M\propto M^{3.78}$, which smooths reheating, suppresses the signal by orders of magnitude, and reopens the ultra-light PBH window.