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arXiv · 1807.01707

Primordial Black Holes from the QCD axion

Francesc Ferrer·Eduard Masso·Giuliano Panico·Oriol Pujolas·Fabrizio Rompineve
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Abstract

We propose a mechanism to generate Primordial Black Holes (PBHs) which is independent of cosmological inflation and occurs slightly below the QCD phase transition. Our setup relies on the collapse of long-lived string-domain wall networks and is naturally realized in QCD axion models with domain wall number $N_{DW}>1$ and Peccei-Quinn symmetry broken after inflation. In our framework, dark matter is mostly composed of axions in the meV mass range along with a small fraction, $Ω_{\text{PBH}} \gtrsim 10^{-6} Ω_{\text{CDM}} $ of heavy $M \sim 10^4-10^7 M_\odot$ PBHs. The latter could play a role in alleviating some of the shortcomings of the $Λ$CDM model on sub-galactic scales. The scenario has distinct signatures in ongoing axion searches as well as gravitational wave observatories.

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Francesc Ferrer, Eduard Masso, Giuliano Panico, Oriol Pujolas, Fabrizio Rompineve. 2019-02-21. Primordial Black Holes from the QCD axion. https://doi.org/10.1103/physrevlett.122.101301

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