Value of the ξ parameter in Kl3 decay from the pion-gauge condition

Abstract

It is shown with the help of the pion-gauge condition that the divergence of the most general boson current in K l 3 decay vanishes in the limit of zero four-momentum of the pion. This in turn implies ξ = − 1 at the (unphysical) point t = m 2 K . Inasmuch as ξ does not seem, experimentally, to vary much with t , the result is significant in the physical region and agrees with experiment.