Kl3 decays in chiral perturbation theory

The process K-l3 is calculated to two-loop order (p(6)) in chiral perturbation theory (ChPT) in the isospin conserved case. We present expressions suitable for use with previous work in two-loop ChPT where the order p(4) parameters (L-i(r)) were determined from experiment. We point out that all the order p(6) parameters (C-i(r)) that appear in the value of f(+)(0) relevant for the determination of \V-us\ can be determined from K-l3 measurements via the slope and the curvature of the scalar form-factor. As by product we update the value of the CKM matrix element \V-us\. (C) 2003 Elsevier B.V. All rights reserved.