Some open questions in K decay

Attention is concentrated on the decays K/sub pi 3/- with respect to the origin of the mod Delta I mod =/sup 1///sub 2/ rule and K/sub mu 3 / - with respect to the breaking of chiral symmetry. Comment is also made on K/sub e4/ and K/sub mu mu / decays. The various isospin amplitudes are extracted from existing data on non-leptonic decays and ambiguities arising from electromagnetic mass differences are displayed. The mod Delta I mod =/sup 3///sub 2/ amplitudes are compared with the pole contribution and with current algebra predictions. The extrapolation of the soft pion theorem for K/sub mu 3 / to the physical region is discussed. Bounds are given for the divergence from factor as a function of chiral symmetry breaking parameters under the assumption of twice subtracted scalar and pseudoscalar propagators. (48 refs).