Abstract
Primordial black hole (PBH) formation during cosmic phase transitions and annihilation periods, such as the QCD transition or the annihilation, is thought to be particularly efficient due to a softening of the equation of state. We present a detailed numerical study of PBH formation during the QCD epoch in order to derive an accurate PBH mass function. We also briefly consider PBH formation during the -annihilation epoch. Our investigation confirms that, for nearly scale-invariant spectra, PBH abundances on the QCD scale are enhanced by a factor compared to a purely radiation dominated Universe. For a power spectrum producing an (almost) scale-invariant PBH mass function outside of the transition, we find a peak mass of with a fraction of the PBHs having a mass of , possibly contributing to the LIGO-Virgo black hole merger detections. We point out that the physics of PBH formation during the -annihilation epoch is more complex as it is very close to the epoch of neutrino decoupling. We argue that neutrinos free-streaming out of overdense regions may actually hinder PBH formation.
5 More- Received 30 June 2023
- Accepted 7 March 2024
DOI:https://doi.org/10.1103/PhysRevD.109.083506
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