Warm Hawking Relics From Primordial Black Hole Domination

TL;DR

This paper investigates how warm relic particles produced by primordial black holes as Hawking radiation influence cosmic structure formation, providing constraints and potential observational signatures to distinguish them from thermal relics.

Contribution

It introduces a detailed model of Hawking relic production and evolution, highlighting their unique momentum distribution and impact on cosmology, which differs from standard thermal relics.

Findings

Hawking relics are produced with larger momenta but in smaller quantities than thermal relics.

They affect large-scale structure growth similarly to eV-scale neutrinos.

Constraints limit Hawking relic abundance to less than 2% of dark matter.

Abstract

We study the cosmological impact of warm, dark-sector relic particles produced as Hawking radiation in a primordial-black-hole-dominated universe before big bang nucleosynthesis. If these dark-sector particles are stable, they would survive to the present day as "Hawking relics" and modify the growth of cosmological structure. We show that such relics are produced with much larger momenta, but in smaller quantities than the familiar thermal relics considered in standard cosmology. Consequently, Hawking relics with keV-MeV masses affect the growth of large-scale structure in a similar way to eV-scale thermal relics like massive neutrinos. We model their production and evolution, and show that their momentum distributions are broader than comparable relics with thermal distributions. Warm Hawking relics affect the growth of cosmological perturbations and we constrain their abundance to be less than $2\%$ of the dark matter over a broad range of their viable parameter space. Finally, we examine how future measurements of the matter power spectrum can distinguish Hawking relics from thermal particles.