Reconciling axion quality with post-inflation cosmology

Abstract

We address the axion quality/cosmology tension that often plagues QCD axion models in post-inflationary Peccei-Quinn (PQ) breaking scenarios. In the proposed framework, the PQ symmetry emerges accidentally from an ${\rm SU}(\mathcal{N})_L\times{\rm SU}(\mathcal{N})_R$ gauge symmetry spontaneously broken to ${\rm SU}(\mathcal{N})_{L+R}$, and its quality is protected because PQ breaking first appears at operator dimension $\mathcal{N}$. Moreover, the construction avoids the domain-wall problem, ensures that no stable fractionally charged relic survives ${\rm SU} (\mathcal{N})_{L+R}$ confinement, and remains free of Landau poles below the scale of PQ-breaking operators. The exotic quarks required to generate the PQ anomaly hadronize into unstable mesons and cosmologically stable neutral baryons. However, plausible arguments indicating a strong suppression of baryon formation in ${\rm SU}(\mathcal{N})$ gauge theories at large $\mathcal{N}$, suggest that their contribution to the dark matter energy density remains subdominant. Combining cosmological constraints with PQ quality and perturbativity requirements yields a viable parameter space in which the axion makes up most of the dark matter and its mass remains predictable.