Primordial black hole dark matter from axion inflation

TL;DR

This paper demonstrates that primordial black holes from axion inflation can constitute all dark matter in the asteroidal mass range, with detectable gravitational wave signatures, by improving theoretical modeling and calculations.

Contribution

It advances the understanding of PBH production during axion inflation by incorporating numerical gauge mode functions and statistical uncertainties, confirming the viability of PBHs as dark matter candidates.

Findings

PBHs can make up all dark matter in the asteroidal mass range.

The mechanism produces a stochastic gravitational wave background detectable by LISA.

The results support the backreaction regime even with low inflaton gradient energy.

Abstract

We revisit the production of primordial black holes (PBHs) by a U(1) gauge field with a pseudo-scalar coupling to the inflaton. We improve upon the existing literature by working in the homogeneous backreaction regime with numerically computed gauge mode functions, adopting state-of-the-art PBH abundance calculations, and incorporating the uncertainty in the statistics of $\delta\rho$. We find that PBHs can account for all of the dark matter in the asteroidal mass range, even when the inflaton gradient energy density is highly subdominant ($10^{-4}$--$10^{-3}$ of the kinetic energy), supporting the validity of the backreaction scheme. This mechanism also unavoidably generates a stochastic gravitational wave background with an amplitude that will be measured at LISA and that will allow to indirectly discriminate between different statistics of $\delta \rho$.