On String Theory Expectations for Photon Couplings to Axion-Like Particles

TL;DR

This paper models axion-like particle (ALP) photon couplings within string theory frameworks, revealing that couplings increase polynomially with the number of ALPs, which has implications for future detection experiments.

Contribution

It provides a novel string theory-based prediction of ALP-photon couplings, highlighting their dependence on the number of ALPs and potential experimental tensions.

Findings

Couplings increase polynomially with the number of ALPs

Expected couplings range from 10^{-12} to 10^{-10} GeV^{-1}

Some predicted couplings are already in tension with existing data

Abstract

ALP-photon couplings are modeled in large ensembles of string vacua and random matrix theories. In all cases, the effective coupling increases polynomially in the number of ALPs, of which hundreds or thousands are expected in the string ensembles, many of which are ultralight. The expected value of the couplings $g_{a\gamma\gamma}\simeq 10^{-12}\text{GeV}^{-1} - 10^{-10}\text{GeV}^{-1}$ provide viable targets for future x-ray telescopes and axion helioscopes, and in some cases are already in tension with existing data.