# The Holographic QCD Axion

## TL;DR

This paper develops a holographic model of the QCD axion using the Witten-Sakai-Sugimoto framework, enabling calculations of axion properties and couplings in strongly coupled regimes, including temperature effects.

## Contribution

It introduces a novel holographic model of the QCD axion based on a gravity dual, allowing for calculable properties and couplings in strongly coupled QCD-like theories.

## Key findings

- Derived the low energy axion Lagrangian and nucleon couplings.
- Analyzed the temperature dependence of the axion mass.
- Calculated the topological susceptibility of strongly coupled ${
m N}=4$ SYM at finite temperature.

## Abstract

A holographic model of QCD axion is presented. It describes a composite axion in the KSVZ class. Having a gravity dual, based on the Witten-Sakai-Sugimoto model, it is calculable in the strongly coupled regime. Its basic properties are derived, including the low energy Lagrangian, from which the axion couplings to nucleons can be derived. Basic features in the deconfined phase are studied as well. In particular, the temperature dependence of the axion mass is extracted from the topological susceptibility. As an aside, the topological susceptibility of strongly coupled ${\cal N}=4$ SYM at finite temperature is derived for the first time.