Calculation of axion-photon-photon coupling in string theory

TL;DR

This paper calculates the axion-photon-photon coupling constant within a specific string theory model, providing a precise value that can inform experimental searches for axions.

Contribution

It presents an exact calculation of the axion-photon-photon coupling in a string compactification with an exact Peccei-Quinn symmetry, including the effects of singlets at the GUT scale.

Findings

Calculated coupling constant $ar{c}_{a\gamma\gamma} = 8/3$ in the model.

Predicted the low-temperature axion coupling $c_{a\gamma\gamma} \\simeq 0.69$ after QCD corrections.

Provides a target value for experimental axion searches.

Abstract

The axion search experiments invite a plausible estimation of the axion--photon--photon coupling constant $\overline{c}_{a\gamma\gamma}$ in string models with phenomenologically acceptable visible sectors. We present the calculation of $\overline{c}_{a\gamma\gamma}$ with an exact Peccei-Quinn symmetry. In the Huh-Kim-Kyae $\Z_{12-I}$ orbifold compactification, we obtain $\overline{c}_{a\gamma\gamma} =\frac{8}{3}$ even with a lot of singlets at the GUT scale, and the low-temperature axion search experiments will probe the QCD corrected coupling, $ {c}_{a\gamma\gamma} \simeq \overline{c}_{a\gamma\gamma}-1.98\simeq 0.69$.