Factoring the Strong CP Problem

TL;DR

This paper introduces a novel multi-axion mechanism involving an $SU(3)^N$ gauge group to naturally solve the strong CP problem, resulting in heavier axions without requiring mirror sectors or new light colored states.

Contribution

It proposes a new multi-axion solution to the strong CP problem that avoids mirror sectors and stabilizing light colored states, expanding the viable parameter space for axion-like particles.

Findings

The mechanism naturally aligns the vacuum to set $ar heta=0$.

Axion masses can be significantly larger than the standard QCD axion.

It avoids introducing discrete symmetries and new light colored states.

Abstract

We present a new mechanism to solve the strong CP problem using $N\geq2$ axions, each dynamically relaxing part of the $\bar\theta$ parameter. At high energies $M\gg\Lambda_{QCD}$ the $SU(3)_{c}$ group becomes the diagonal subgroup of an $SU(3)^{N}$ gauge group, and the non-perturbative effects in each individual $SU(3)$ factor generate a potential for the corresponding axion. The vacuum is naturally aligned to ensure $\bar\theta=0$ at low energies, and the masses of these axions can be much larger than for the standard QCD axion. This mechanism avoids the introduction of a discrete $Z_2$ symmetry and associated 'mirror' copies of the SM fermions, and also avoids the introduction and stabilization of new light colored states to modify the running of the QCD gauge coupling found in other heavy axion models. This strengthens the motivation for axion-like particles solving the strong CP problem at points beyond the standard QCD axion curve in the $(m_a, f_a)$ plane.