Quark masses and chiral symmetry

I discuss the global structure of the strongly interacting gauge theory of quarks and gluons as a function of the quark masses and the CP-violating parameter {θ}. I concentration on whether a first order phase transition occurs at {θ}={π}. I show why this is expected when multiple flavors have a small degenerate mass. This transition can be removed by sufficient flavor breaking. I speculate on the implications of this structure for Wilson's lattice fermions.