PCAC anomalies and π⁰ photoproductionphotoproduction

The Adler anomaly is applied to π⁰ photoproduction at threshold in the framework of a quark-vector gluon model. The anomalous contributions may account for the possible discrepancy between the predicted and measured values of the M _1± multipoles. With a «reasonable» quark-gluon coupling constant the data favour a three-tripletquark model (as is the case for π⁰→2γ). The range and errors of the existing theoretical analyses prevent firm conclusions from being drawn. The effect may serve as a sensitive test for the validity of the vectorgluon model.