Probing modified Hawking evaporation with gravitational waves from the primordial black hole dominated universe

TL;DR

This paper investigates how a proposed slowdown in Hawking black hole evaporation, called 'memory burden', affects primordial black hole evolution, gravitational wave signals, and the potential to test these effects observationally.

Contribution

It introduces the impact of memory burden on PBH reheating, showing extended PBH lifetimes and altered GW signatures, providing a novel way to test Hawking evaporation modifications.

Findings

Longer PBH dominated phase due to memory burden.

GW frequency bound above 1 Hz with enhanced amplitude.

Potential to detect Hawking evaporation modifications via GW spectrum slope.

Abstract

It has been recently proposed that Hawking evaporation might slow down after a black hole has lost about half of its mass. Such an effect, called "memory burden", is parameterized as a suppression in the mass loss rate by negative powers $n$ of the black hole entropy and could considerably extend the lifetime of a black hole. We study the impact of memory burden on the Primordial Black Hole (PBH) reheating scenario. Modified PBH evaporation leads to a significantly longer PBH dominated stage. Requiring that PBHs evaporate prior enough to Big Bang Nucleosynthesis shrinks the allowed PBH mass range. Indeed, we find that for $n>2.5$ the PBH reheating scenario is not viable. The frequency of the Gravitational Waves (GWs) induced by PBH number density fluctuations is bound to be larger than about a Hz, while the amplitude of the GW spectrum is enhanced due to the longer PBH dominated phase. Interestingly, we show that, in some models, the slope of the induced GW spectrum might be sensitive to the modifications to Hawking evaporation, proving it may be possible to test the "memory burden" effect via induced GWs. Lastly, we argue that our results could also apply to general modifications of Hawking evaporation.