Form Factors inKμ3andKe3Decay

An investigation of the form factors in $K_{\mu 3}$ and $K_{e3\mathrm{}}$ decay amplitudes, on the assumption of local production of the fermion pair, is carried out by means of dispersion relation techniques. The approximation is made of taking explicit account of $K-\pi$ scattering in the unitarity condition and incorporating all the other contributions into a single arbitrary parameter. The validity of this approximation is discussed. The results are expressed in terms of $S$ and $P$ phase shifts for $K-\pi$ scattering.