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.
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