The Drell-Hearn-Gerasimov Sum-Rule in QCD

Abstract

Photoproduction spin sum-rules offer a new window on the spin structure of the nucleon that complements the information we can learn from polarised deep inelastic scattering experiments. We review the theory and present status of the Drell-Hearn-Gerasimov sum-rule in QCD, emphasising the possible relation between the present ``discrepancy'' in this sum-rule and the nucleon's strangeness magnetic moment. In the case of an elementary electron or photon target (say at the NLC) the Drell-Hearn-Gerasimov sum-rule provides a test for physics beyond the minimal Standard Model.

Comments: 19 pages, LaTeX, no figures; various typos fixed; to appear in Mod. Phys. Letts. A