The Axion is Going Dark

TL;DR

This paper investigates how a non-Abelian dark sector coupled to the axion can alter its topological couplings and lower bounds on axion-photon interactions, revealing new possibilities for axion phenomenology.

Contribution

It introduces a novel framework where dark sector gauge groups modify axion topological couplings through topological mixing, expanding the landscape of axion models.

Findings

Lower bounds on axion-photon coupling can be significantly reduced.

Allowed exotic matter representations are constrained by topological mixing.

Generalized categorical symmetries of axion theories are characterized.

Abstract

In this work we explore the effect of a non-Abelian dark sector gauge group that couples to the axion field. In particular, we analyze effects that arise if the dark sector gauge group mixes topologically with the Standard Model. This is achieved by gauging a subgroup of the global center 1-form symmetries which embeds non-trivially in both the visible as well as the dark sector gauge groups. Leaving the local dynamics unchanged, this effect modifies the quantization conditions for the topological couplings of the axion, which enter the estimate of a lower bound on the axion-photon coupling. In the presence of a dark sector this lower bound can be reduced significantly, which might open up interesting new parameter regions for axion physics. We further determine the allowed exotic matter representations in the presence of topological mixing with a dark sector, explore the generalized categorical symmetries of such axion theories, and comment on other model-independent phenomenological consequences.