K-L4 DECAYS BEYOND ONE-LOOP

The matrix elements for K --> pi pi l nu decays are described by four form factors F, G, H and R. We complete previous calculations by evalu ating R at next-to-leading order in the low-energy expansion. We then estimate higher order contributions using dispersion relations and det ermine the low-energy constants L(1), L(2) and L(3) from data on K-e4 decays and on elastic pion scattering. Finally, we present predictions for the slope of the form factor G and for total decay rates.