Axion as a CDM component

TL;DR

This paper reviews the QCD axion's role in solving the strong CP problem and its potential as a dark matter component, discussing theoretical aspects, astrophysical effects, and implications from string theory.

Contribution

It provides a comprehensive overview of the QCD axion's theoretical motivation, astrophysical implications, and the possibility of detection within string theory frameworks.

Findings

QCD axion addresses the strong CP problem

Axion could be a significant dark matter component

String theory may or may not produce a detectable axion

Abstract

I discuss the essential features of the QCD axion: the strong CP solution and hence its theoretical necessity. I also review the effects of the QCD axion on astrophysics and cosmology, in particular with emphasis on its role in the dark matter component together with its supersymmetric partner axino. It is pointed out that string theory may or may not give a detectable QCD axion.