Compact extra-dimensions as solution to the strong CP problem

TL;DR

This paper proposes a novel approach to solving the strong CP problem by utilizing extra compact dimensions, demonstrating that the problem can be addressed without axion-like particles in a higher-dimensional framework.

Contribution

It introduces a higher-dimensional model with trivial vacuum structure that dynamically solves the strong CP problem without requiring axions.

Findings

The model reproduces QCD's perturbative properties in the low-energy limit.

The vacuum structure remains trivial in the weak coupling regime.

No axion-like particles are produced, avoiding astrophysical constraints.

Abstract

We show that the strong CP problem can, in principle, be solved dynamically by adding extra-dimensions with compact topology. To this aim we consider a toy model for QCD, which contains a vacuum angle and a strong CP like problem. We further consider a higher dimensional theory, which has a trivial vacuum structure and which reproduces the perturbative properties of the toy model in the low-energy limit. In the weak coupling regime, where our computations are valid, we show that the vacuum structure of the low-energy action is still trivial and the strong CP problem is solved. No axion-like particle occur in this setup and therefore it is not ruled out by astrophysical bounds.