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

Understand

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.