Axion as a CDM component

Understand

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.