FK/Fpi from the Budapest-Marseille-Wuppertal Collaboration
  Based on a series of lattice calculations we determine the ratio FK/Fpi in QCD. With experimental data from kaon decay and nuclear double beta decay, we obtain a precise determination of |Vus|. Our simulation includes 2+1 flavours of sea quarks, with three lattice spacings, large volumes and a simulated pion mass reaching down to about 190 MeV for a full control over the systematic uncertainties. 
A. Ramos, S. Durr, Z. Fodor, C. Hoelbling, S. D. Katz, S. Krieg, T.   Kurth, L. Lellouch, T. Lippert, K. K. Szabo
hep-lat hep-ph