Anomalies and discrete chiral symmetries

Abstract

The quantum anomaly that breaks the U(1) axial symmetry of massless multi-flavored QCD leaves behind a discrete flavor-singlet chiral invariance. With massive quarks, this residual symmetry has a close connection with the strong CP-violating parameter theta. One result is that if the lightest quarks are degenerate, then a first order transition will occur when theta passes through pi. The resulting framework helps clarify when the rooting prescription for extrapolating in the number of flavors is valid.

arXiv comment12 pages, 7 figures. Contribution to the International Workshop on QCD Green's Functions, Confinement and Phenomenology September 7-11, 2009, ECT Trento, Italy. Revised version adds references