Catalogues of cosmologically self-consistent hadronic QCD axion models

Abstract

We extend the catalogue of “phenomenologically preferred” hadronic axion models to include heavy fermion representations associated with higher-dimensional decay operators. The latter have recently been shown to self-consistently trigger a period of early matter domination, making the underlying axion models cosmologically viable. After identifying all possible representations up to decay operator dimension d ≤ 9, we update the hadronic axion band for the axion-photon coupling. The central regions of the axion band are similar to those found previously and approximately independent of the axion decay constant fa, suggesting that they are robust predictions and targets for future axion searches. Moreover, we find that d = 6 and d = 7 operators can lead to two new viable “model islands” around fa ∼ 1012 GeV and fa ∼ 1014 GeV, i.e., beyond the standard post-inflationary mass region.