The matrix elements for K→ππ\lν decays are described by four form factors F,G,H and R. We complete previous calculations by evaluating R at next-to-leading order in the low-energy expansion. We then estimate higher order contributions using dispersion relations and determine the low-energy constants L1,L2 and L3 from data on Ke4 decays and on elastic pion scattering. Finally, we present predictions for the slope of the form factor G and for total decay rates.
@article{arxiv.hep-ph/9403390,
title = {$K_{l4}$ - Decays Beyond One Loop},
author = {J. Bijnens and G. Colangelo and J. Gasser},
journal= {arXiv preprint arXiv:hep-ph/9403390},
year = {2009}
}