Protecting the axion with local baryon number

The Peccei–Quinn (PQ) solution to the Strong CP Problem is expected to fail unless the global symmetry U(1)_PQ is protected from Planck-scale operators up to high mass dimension. Suitable protection can be achieved if the PQ symmetry is an automatic consequence of some gauge symmetry. We highlight that if baryon number is promoted to a gauge symmetry, the exotic fermions needed for anomaly cancellation can elegantly provide an implementation of the Kim–Shifman–Vainshtein–Zakharov 'hidden axion' mechanism with a PQ symmetry protected from Planck-scale physics.