Towards a post-inflationary composite axion model

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 NDW = 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.