Numerical simulation of QCD with u, d, s and c quarks in the twisted-mass Wilson formulation T. Chiarappa, F. Farchioni, K. Jansen, I. Montvay, E.E. Scholz, L. Scorzato, T. Sudmann and C. Urbach Eur. Phys. J. C, 50 2 (2007) 373-383 Published online: 10 February 2007 DOI: 10.1140/epjc/s10052-006-0204-4