Note on the strong CP problem from a 5-dimensional perspective

TL;DR

This paper explores a 5-dimensional gauge theory with a compactified extra dimension, proposing a model where a U(1)_X gauge field acts as an axion to address the strong CP problem, with detailed phenomenological analysis.

Contribution

It introduces a novel 5D model with a bulk Chern-Simons term and an extra U(1)_X gauge field that naturally solves the strong CP problem via an axion-like mechanism.

Findings

The model successfully avoids most experimental constraints.

The axion-like field effectively solves the strong CP problem.

Detailed phenomenological implications are discussed.

Abstract

We consider 5 dimensional gauge theories where the 5th direction is compactified on an interval. The Chern-Simons (CS) terms (favored by naive dimensional analysis) are discussed. A simple scenario with an extra U(1)_X gauge field that couples to SU(3)_{color} through a CS term in the bulk is constructed. The extra component of the Abelian gauge field plays a role of the axion, which in the standard manner solves the strong CP problem easily avoiding most of experimental constraints. This version has an expanded discussion of the phenomenology of the model and various clarifications in the estimation of the operator coefficients in the appendix.