Warped QCD without the strong CP problem

QCD in a five-dimensional sliced AdS bulk with chiral extra-quarks on the boundaries is generically free from the strong CP problem. Accidental axial symmetry is naturally present except for suppressed breaking interactions, which plays a role of the Peccei–Quinn symmetry to make the strong CP phase sufficiently small. Breaking suppression and enhancement due to AdS warping are considered in addition to naive boundary separation effects.