Application of Current Algebra Techniques to Neutral-Current-Induced Threshold Pion Production

I apply current-algebra techniques to study threshold pion production induced by the weak neutral current. In addition to specific predictions for the Weinberg-Salam-model current, I find upper bounds on the magnitude of threshold pion production for an isoscalar neutral current and for a general hadronic neutral current formed from the usual vector and axial-vector nonets. Violation of these bounds would suggest the presence of new coupling types in the neutral semileptonic interaction.