Robustness of the dispersive representation of Kπ form factors

Some time ago a dispersive representation of the scalar Kπ form factor has been proposed. It does not only allow to limit the number of free parameters in the analysis of the experimental Kl3 decay data on physically motivated ground, but the main interest is that it allows via the Callan-Treiman low-energy theorem to test the standard model precisely. This asks for a detailed study of the uncertainties of the dispersive representation which will be presented here. In addition, a dispesive representation of the vector form factor together with its uncertainties will be discussed.