Pinning down the primordial black hole formation mechanism with gamma-rays and gravitational waves

TL;DR

This paper explores how gamma-ray and gravitational wave observations can identify the formation mechanisms of asteroid-mass primordial black holes, covering four specific models and their mass functions.

Contribution

It introduces a combined observational approach using gamma-rays and GWs to distinguish among four primordial black hole formation mechanisms.

Findings

Gamma-ray and GW signals can probe PBHs up to 10^{19} g.

Different formation mechanisms produce distinguishable signals.

Combined signals help identify the physical origin of PBHs.

Abstract

Primordial black holes (PBHs) are predicted in many models via different formation mechanisms. Identifying the origin of PBHs is of the same importance as probing their existence. We propose to probe the asteroid-mass PBHs [$\mathcal{O}(10^{17})~{\rm g}\lesssim M\lesssim\mathcal{O}(10^{22})~{\rm g}$] with gamma-rays from Hawking radiation and the stochastic gravitational waves (GWs) from the early Universe. We consider four concrete formation mechanisms, including collapse from primordial curvature perturbations, first-order phase transitions, or cosmic strings, and derive the extended PBH mass functions of each mechanism for phenomenological study. The results demonstrate that by combining gamma-rays and GW signals we can probe PBHs up to $\mathcal{O}(10^{19})~{\rm g}$ and identify their physical origins.