Memory burden effect mimics reheating signatures on SGWB from ultra-low mass PBH domination

TL;DR

This paper investigates how the memory burden effect during the evaporation of ultra-low mass primordial black holes can mimic reheating signatures in the stochastic gravitational wave background, complicating their interpretation.

Contribution

It demonstrates that the memory burden effect can produce SGWB signals similar to those from non-standard reheating, revealing a degeneracy in observational signatures.

Findings

Memory burden effects can mimic reheating signatures in SGWB.

Degeneracy between PBH evaporation effects and reheating can be broken by detecting the first peak.

SGWB spectrum features depend critically on PBH evaporation and inflationary perturbations.

Abstract

Ultra-low mass primordial black holes (PBH), briefly dominating the expansion of the universe, would leave detectable imprints in the secondary stochastic gravitational wave background (SGWB). Such a scenario leads to a characteristic doubly peaked spectrum of SGWB and strongly depends on the Hawking evaporation of such light PBHs. However, these observable signatures are significantly altered if the memory burden effect during the evaporation of PBHs is taken into account. We show that for the SGWB induced by PBH density fluctuations, the memory burden effects on the Hawking evaporation of ultra-low mass PBHs can mimic the signal arising due to the non-standard reheating epoch before PBH domination. Finally, we point out that this degeneracy can be broken by the simultaneous detection of the first peak in the SGWB, which is typically induced by the inflationary adiabatic perturbations.