# Spontaneous symmetry breaking by axions?

I am just reading at the beginnin of this nice article, that axions could be responsible for spontaneously breaking of a symmetry in the early universe.

Does anybody know which symmetry is alluded to and how the mechanism of spontaneous symmetry breaking exactly works in this particular case?

• The original axion model has a global $U(1)$ Peccei-Quinn symmetry which is spontaneously broken, but this has been ruled out. Nowadays people look at elaborated versions of the basic idea. A quick look at the Pospelov et al. preprint mentioned in the article shows they study a $Z_n$ invariant scalar. I'm really not very familiar with the details of these models though. PDG has a nice review. Jul 3, 2013 at 11:50