Bounds on the form factor of $K_{l3}$ decay

The author derives bounds on the form factor f(t) of K/sub l3/ decay valid from the origin to the threshold (m/sub pi /+m/sub K/)/sup 2/. If he uses as input the soft-pion theorem on f/sub +or-/(t) and a bound on the propagator Delta (0) of the divergence of the strangeness changing current at zero momentum, he obtains an upper and lower bound, which are close together but which do not fit with experiment; by allowing Delta (0) to vary as a free parameter, there is then better agreement. He also discusses some bounds for the decay parameters. (13 refs).