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.

Automated summary

The PQ mechanism addresses the strong CP problem but introduces challenges in model building, related to the origin, scale, and quality of the PQ symmetry. A UV completed model with extra quarks and anti-quarks separated by branes, along with a hidden gauge field condensation, is proposed to tackle these challenges. The Casimir force of SU(N-H) condensation stabilizes the fifth dimension and ensures the quality of the PQ symmetry.