Leptonic coupling-types in K+ → π++- decays and the question of strangeness-changing semileptonic neutral currents

A study of the leptonic coupling types in K⁺→π⁺?⁺?^? (? = e, μ) provides come model-independent distinction between the various underlying mechanism: lowest order weak cum electromagnetic vs higher order weak interactions vs genuine strangeness-changing semileptonic neutral currents. This distinction is necessary in order to know the existence of these neutral currents. Pion energy spectrum for ? = e and the ratio of the total rate for ? = e to that for ? = μ is useful for this purpose, and the pion energy spectrum for ? = μ is of further help. Available data (? = eonly) are inadequate to provide the above distinction. Estimates of various coupling strengths are made from the observed ? = e rate.