  We investigate the kaon semileptonic decay (K_{l3}) form factors within the
framework of the nonlocal chiral quark model from the instanton vacuum, taking
into account the effects of flavor SU(3) symmetry breaking. All theoretical
calculations are carried out without any adjustable parameter. We also show
that the present results satisfy the Callan-Treiman low-energy theorem as well
as the Ademollo-Gatto theorem. It turns out that the effects of flavor SU(3)
symmetry breaking are essential in reproducing the kaon semileptonic form
factors. The present results are in a good agreement with experiments, and are
compatible with other model calculations.

High Energy Physics - Phenomenology