A dispersive treatment ofK_ℓ4decays

Abstract

Abstract. The K 4 decay is one of the best sources of information on some low-energy constants of chiral perturbation theory (χPT). We present a dispersive approach to K 4 decays, which takes rescattering effects fully into account. The dispersion relation treats both experimentally accessible form factors simultaneously and also describes the dependence on the dilepton invariant mass. We apply isospin-breaking corrections before fitting the data of NA48/2 and E865 experiments and extract the values of the low-energy constants L r 1 , L r 2 and L r 3 from a matching to χPT.