Abstract
We investigate the 2-flavor QCD with non-degenerate quark masses at low-energy, using the chiral perturbation theory including the h meson and anomaly effects. For the fixed md 6 0, the neutral pion becomes massless at two values of mu, between which a spontaneously CP broken phase appears with the neutral pion condensation. We then show that the topological susceptibility diverges at these two critical points. We also consider the case of mu =md but q =p, equivalently mu = md with q = 0 by the chiral rotation and show that the CP symmetry is spontaneously broken by the h condensation at small m. Around m = 0, three pions become Nambu-Goldstone modes, showing non-standard behavior that m 2 = O(m 2 ), which, however, is consistent with the chiral Ward-Takahashi identities.
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