  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.

High Energy Physics - Phenomenology