2000 character limit reached
Why PQ? (1005.0643v1)
Published 4 May 2010 in hep-ph and hep-th
Abstract: I discuss how the solution of the $U(1)A$ problem of QCD through the existence of the $\theta$-vacuum gave rise to the strong CP problem. After examining various suggested solutions to this problem, I conclude that the only viable solution still is the one that involves the existence of a spontaneously broken chiral symmetry: $U(1){PQ}$