More axions from diluted domain walls

TL;DR

This paper explores a scenario where axion production from a string-domain wall network after inflation leads to higher axion abundance, allowing lower decay constants to account for dark matter, and discusses models realizing this scenario.

Contribution

It introduces a novel scenario where post-inflationary string-domain wall networks significantly increase axion abundance, expanding viable parameter space for axion dark matter.

Findings

Axion abundance can be much larger than in conventional scenarios.

Lower axion decay constants (~10^8 GeV) can explain dark matter.

Produced axion mini-halos are more massive than in standard models.

Abstract

We consider the scenario in which the Peccei-Quinn symmetry breaking is followed by a period of inflation. A particularly interesting case is that the string-domain wall network produced by the symmetry breaking enters the horizon after the QCD phase transition. We show that the abundance of axions produced by such a string-domain wall network is counterintuitively much larger than the conventional post-inflationary Peccei-Quinn symmetry breaking scenario. As a result, a scenario with the axion decay constant even as low as the astrophysical bound of about $10^8$ GeV can explain the observed abundance of dark matter. The axion mini-halos produced from the string-domain wall network is much more massive than the conventional scenario. We also briefly discuss models which can realize this scenario such as a Peccei-Quinn phase transition during inflation or a second inflation after a Peccei-Quinn phase transition.