Numerical simulation of QCD with u, d, s and c quarks in the   twisted-mass Wilson formulation
  A first study of numerical Monte Carlo simulations with two quark doublets, a mass-degenerate one and a mass-split one, interpreted as u, d, s and c quarks, is carried out in the framework of the twisted mass Wilson lattice formulation. Tuning the bare parameters of this theory is explored on 12^3x24 and 16^3x32 lattices at lattice spacings a=0.20fm and a=0.15fm, respectively. 
T.Chiarappa, F.Farchioni, K.Jansen, I.Montvay, E.E.Scholz, L.Scorzato,   T.Sudmann, C.Urbach