GUT-Scale Primordial Black Holes: Consequences and Constraints

TL;DR

This paper explores the implications of very light primordial black holes evaporating before nucleosynthesis, focusing on their gravitational wave signatures and potential effects on early universe expansion.

Contribution

It demonstrates that graviton radiation from evaporating black holes produces a detectable high-frequency gravitational wave background and analyzes their impact on early universe dynamics.

Findings

Hawking radiation from primordial black holes sources a high-frequency gravitational wave background.

Evaporating black holes could cause a transient matter-dominated era in the early universe.

The gravitational wave spectrum is independent of initial black hole density.

Abstract

A population of very light primordial black holes which evaporate before nucleosynthesis begins is unconstrained unless the decaying black holes leave stable relics. We show that gravitons Hawking radiated from these black holes would source a substantial stochastic background of high frequency gravititational waves ($10^{12}$ Hz or more) in the present universe. These black holes may lead to a transient period of matter dominated expansion. In this case the primordial universe could be temporarily dominated by large clusters of "Hawking stars" and the resulting gravitational wave spectrum is independent of the initial number density of primordial black holes.