Contributions of order O(m(quark)**2) K(lepton 3) form-factors and unitarity of the CKM matrix
Résumé
The form factors for the K_{l 3} semileptonic decay are computed to order O(p^4) in generalized chiral perturbation theory. The main difference with the standard O(p^4) expressions consists in contributions quadratic in quark masses, which are described by a single divergence-free low-energy constant, A_3. A new simultaneous analysis is presented for the CKM matrix element V_{us}, the ratio F_K/F_{pi}, K_{l 3} decay rates and the scalar form factor slope lambda_0. This framework easily accommodates the precise value for $V_{ud}$ deduced from superallowed nuclear beta-decays.
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