Accidental SO(10) axion from gauged flavour

An accidental U(1) Peccei-Quinn (PQ) symmetry automatically arises in a class of SO(10) unified theories upon gauging the SU(3)_f flavour group. The PQ symmetry is protected by the &Z;₄ × &Z;₃ center of SO(10) × SU(3)_f up to effective operators of canonical dimension six. However, high-scale contributions to the axion potential posing a PQ quality problem arise only at d = 9. In the pre-inflationary PQ breaking scenario the axion mass window is predicted to be m_a ∈ [7 × 10^-8, 10^-3] eV, where the lower end is bounded by the seesaw scale and the upper end by iso-curvature fluctuations. A high-quality axion, that is immune to the PQ quality problem, is obtained for m_a ≳ 2 0.02 eV. We finally offer a general perspective on the PQ quality problem in grand unified theories.