Leptonic decay-constant ratio fK/fπ from lattice QCD using 2+1 clover-improved fermion flavors with 2-HEX smearing

Abstract

We present a calculation of the leptonic decay-constant ratio f(kappa)/f(pi) in 2+1 flavor QCD. Our data set includes five lattice spacings and pion masses reaching down below the physical one. Special emphasis is placed on a careful study of all systematic uncertainties, especially the continuum extrapolation. Our result is perfectly compatible with the first-row unitarity constraint of the Standard Model.