Twisted mass quarks and the phase structure of lattice QCD
  The phase structure of zero temperature twisted mass lattice QCD is investigated. We find strong metastabilities in the plaquette observable when the untwisted quark mass assumes positive or negative values. We provide interpretations of this phenomenon in terms of chiral symmetry breaking and the effective potential model of Sharpe and Singleton. 
F. Farchioni, R. Frezzotti, K. Jansen, I. Montvay, G.C. Rossi, E.   Scholz, A. Shindler, N. Ukita, C. Urbach, I. Wetzorke