THE ADLER-BARDEEN THEOREM FOR THE AXIAL U(1) ANOMALY IN A GENERAL NON-ABELIAN GAUGE THEORY

A general, regularization-scheme-independent proof of the nonrenormalization theorem for the anomaly of a U(1) axial current in a renormalizable gauge theory is presented. The gauge group may be an arbitrary compact Lie group. The validity of the theorem is traced back to some finiteness properties allowing for a well defined but particular choice of the anomaly operators. Whereas in the case of a purely Abelian gauge group this choice amounts to a physically reasonable normalization at zero energy, the general non-Abelian case awaits a deeper understanding.