Twisted mass fermions: neutral pion masses from disconnected   contributions
  Twisted mass fermions allow light quarks to be explored but with the consequence that there are mass splittings, such as between the neutral and charged pion. Using a direct calculation of the connected neutral pion correlator and stochastic methods to evaluate the disconnected correlations, we determine the neutral pion mass. We explore the dependence on lattice spacing and quark mass in quenched QCD. For dynamical QCD, we determine the sign of the splitting which is linked, via chiral PT, to the nature of the phase transition at small quark mass. 
F. Farchioni, K. Jansen, C. McNeile, C. Michael, I. Montvay, K. Nagai,   M. Papinutto, J. Pickavance, E. Scholz, L. Scorzato...