A Chiral Nelson-Barr Relaxion

We present the chiral Nelson-Barr relaxion model, an extension of the Nelson-Barr relaxion framework with a gauged chiral $\mathrm{U}(1)$ symmetry. It includes vector-like quarks to cancel gauge anomalies and a scalar whose vacuum expectation value generates their masses. The chiral symmetry forbids the leading operators responsible for the Nelson-Barr and clockwork quality problems. Right-handed neutrinos generate light-neutrino masses through the type-I seesaw mechanism and permit thermal leptogenesis. For the particular coupling considered, relaxion phenomenology gives $f_{\mathrm{m}\mathrm{a}\mathrm{x}}^{\mathrm{p}\mathrm{h}\mathrm{e}\mathrm{n}\mathrm{o}}\sim 4\times {10}^{11}\mathrm{G}\mathrm{e}\mathrm{V}$, about eight times the corresponding phenomenological ceiling in the original model. The model can accommodate thermal leptogenesis if its right-handed-neutrino masses and reheating history satisfy the required temperature bounds.