K ->pi l nu semileptonic form factors from two-flavor lattice QCD

Abstract

We present new lattice results of the K ->pi l nu semileptonic form factors obtained from simulations with two flavors of dynamicaltwisted-mass fermions, using pion masses as light as 260 MeV. Our main result is f(+)(0)=0.9560(84), which, combined with the latest experimental data for Kl3 decays, leads to |Vus|=0.2267(5)(exp)(20)(f+(0)). Using the PDG(2008) determinations of|Vud| and |Vub| our result implies for the unitarity relation |Vud|^2+|Vus|^2+|Vub|^2=1.0004(15). For the O(p^6) term of the chiral expansion of f+(0) we get Delta f = f+(0)-1-f2=-0.0214(84).