Light quark masses and pseudoscalar decay constants from Nf = 2 lattice QCD with twisted mass fermions

We present the results of a lattice QCD calculation of the average up-down and strange quark masses and of the light meson pseudoscalar decay constants with Nf = 2 dynamical fermions. The simulation is carried out at a single value of the lattice spacing with the twisted mass fermionic action at maximal twist, which guarantees automatic O(a)-improvement of the physical quantities. Quark masses are renormalized by implementing the non perturbative RI-MOM renormalization procedure. Our results for the light quark masses are mudMS-bar(2 GeV) = 3.85±0.12±0.40 MeV, msMS-bar(2 GeV) = 105±3±9 MeV and ms/mud = 27.3±0.3±1.2. We also obtain fK = 161.7±1.2±3.1 MeV and the ratio fK/fπ = 1.227±0.009±0.024. From this ratio, by using the experimental determination of Γ(K → μν-bar μ(γ))/Γ(π → μν-bar μ(γ)) and the average value of |Vud| from nuclear beta decays, we obtain |Vus| = 0.2192(5)(45), in agreement with the determination from Kl3 decays and the unitarity constraint