Kπlνsemileptonic form factors from two-flavor lattice QCD

Abstract
We present new lattice results of the Kπν semileptonic form factors obtained from simulations with two flavors of dynamical twisted-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 K3 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(p6) term of the chiral expansion of f+(0) we get Δff+(0)1f2=0.0214(84).
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