Are there ALPs in the asymptotically safe landscape?

TL;DR

This paper explores the possibility of axion-like particles (ALPs) within asymptotically safe gravity-matter theories, concluding that fundamental ALPs are unlikely to be compatible with such frameworks, making their experimental detection significant for understanding quantum gravity.

Contribution

It analyzes the behavior of ALP-photon interactions in asymptotically safe gravity-matter systems and assesses their compatibility, providing new insights into quantum gravity constraints.

Findings

ALP-photon coupling can become asymptotically safe or free.

Strong gravity needed to alter ALP interactions conflicts with asymptotic safety bounds.

Fundamental ALPs are likely incompatible with asymptotically safe gravity-matter systems.

Abstract

We investigate axion-like particles (ALPs) in the context of asymptotically safe gravity-matter systems. The ALP-photon interaction, which facilitates experimental searches for ALPs, is a dimension-5-operator. Quantum fluctuations of gravity lower its scaling dimension, and the ALP-photon coupling can become asymptotically free or even asymptotically safe. However, quantum fluctuations of gravity need to be strong to overcome the canonical scaling and this strong-gravity regime is in tension with the weak-gravity bound in asymptotic safety. Thus, we tentatively conclude that fundamental ALPs can likely not be accommodated in asymptotically safe gravity-matter systems. In turn, an experimental discovery of an ALP would thus shed valuable light on the quantum nature of gravity.