Towards a post-inflationary composite axion model

A bstract Composite axions offer a scenario where the axion emerges as a pion-like state, avoiding fine-tuning of elementary scalars and ameliorating the axion quality problem. Despite these advantages, their post-inflationary cosmology remains largely unexplored, with challenges including the domain wall problem and the presence of exotic relics. We propose two composite axion models with an effective domain wall number N DW = 1 and study the dilution of relics via a short period of inflation. One model is based on an SU(5) chiral gauge theory, while the other employs a “gauged” U(1) Peccei-Quinn symmetry in vector-like SU( N ) gauge theories. We identify the viable parameter space in which axion strings re-enter the horizon before or even after the QCD transition and axion dark matter is dominantly produced from the decay of the string-wall network.