Flavour Breaking Effects of Wilson twisted mass fermions
  We study the flavour breaking effects appearing in the Wilson twisted mass formulation of lattice QCD. In this quenched study, we focus on the mass splitting between the neutral and the charged pion, determining the neutral pion mass with a stochastic noise method to evaluate the disconnected contributions. We find that these disconnected contributions are significant. Using the Osterwalder-Seiler interpretation of the connected piece of the neutral pion correlator, we compute the corresponding neutral pion mass to study with more precision the scaling behaviour of the mass splitting. 
K. Jansen, C. McNeile, C. Michael, K. Nagai, M. Papinutto, J.   Pickavance, A. Shindler, C. Urbach, I. Wetzorke