Why PQ
/ Authors
/ Abstract
I discuss how the solution of the U(1)A problem of QCD through the existence of the θ -vacuum gave rise to the strong CP problem. After examining v arious suggested solutions to this problem, I conclude that the only viable solution still is one that involves the existence of a spontaneously broken chiral symmetry: U(1)PQ.
DOI: 10.1063/1.3489562