Small Momentum Evolution of the Extended Drell--Hearn--Gerasimov Sum Rule

Abstract

We investigate the momentum dependence of the extended Drell-Hearn-Gerasimov sum rule. An economical formalism is developed which allows to express the extended DHG sum rule in terms of a single virtual Compton amplitude in forward direction. Rigorous results for the small momentum evolution are derived from chiral perturbation theory within the one-loop approximation. Furthermore, we evaluate some higher order contributions arising from $\Delta (1232)$ intermediate states and relativistic corrections. (2 figures available upon request).

Comments: 12 pages, TeX, BUTP-92/51 and CRN-92-53