Equal-time commutators and photoproduction sum rules

Abstract

Generalized sum rules derived from equal-time commutators for arbitrary values of momentum transfer square are given for photoproduction amplitudes. In particular, it is shown that, in the decuplet dominant model, the electric quadrupole transition part of the γNN^∗ vertex has to vanish, which seems to be true experimentally. However, the sum rule for the anomalous magnetic moments of the nucleons obtained from charged photoproduction amplitudes does not seem to hold in this approximation. Possible reasons for this discrepancy are discussed.