A natural and simple UV completion of the QCD axion model

The novel PQ mechanism replaces the strong CP problem with some challenges in a model building. In particular, the challenges arise regarding i) the origin of an anomalous global symmetry called a PQ symmetry, ii) the scale of the PQ symmetry breaking, and iii) the quality of the PQ symmetry. In this letter, we provide a natural and simple UV completed model that addresses these challenges. Extra quarks and anti-quarks are separated by two branes in the Randall-Sundrum R-4 x S-1/Z(2) spacetime while a hidden SU(N-H) gauge field condensates in the bulk. The brane separation is the origin of the PQ symmetry and its breaking scale is given by the dynamical scale of the SU(N-H) gauge interaction. The (generalized) Casimir force of SU(N-H) condensation stabilizes the 5th dimension, which guarantees the quality of the PQ symmetry. (C) 2021 The Author(s). Published by Elsevier B.V.