K→πlν semileptonic form factors from two-flavor lattice QCD

Abstract

We present new lattice results of the K → π ℓ ν 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 K ℓ 3 decays, leads to | V u s | = 0.2267 ( 5 ) exp  ( 20 ) f + ( 0 ) . Using the PDG(2008) determinations of | V u d | and | V u b | our result implies for the unitarity relation | V u d | 2 + | V u s | 2 + | V u b | 2 = 1.0004 ( 15 ) . For the O ( p 6 ) term of the chiral expansion of f + ( 0 ) we get Δ f ≡ f + ( 0 ) − 1 − f 2 = − 0.0214 ( 84 ) .