Generalized sum rules for spin-dependent structure functions of the nucleon

The Drell-Hearn-Gerasimov and Bjorken sum rules are special examples of dispersive sum rules for the spin-dependent structure function G(1)(nu, Q(2)) at Q(2) = 0 and infinity. We generalize these sum rules through studying the virtual-photon Compton amplitudes S-1(nu, Q(2)) and S-2(nu, Q(2)) At small Q(2), we calculate the Compton amplitudes at leading order in chiral perturbation theory; the resulting sum rules will be ableto be tested against data soon available from the Jefferson Laboratory. For Q(2) much greater than Lambda (2)(QCD) the standard twist-expansion for the Compton amplitudes leads to the well known deep-inelastic sum rules. Although the situation is still relatively unclear in a small intermediate-Q(2) window, we argue that chiral perturbation theory and the twist-expansion alone already provide strong constraints on the Q(2)-evolution of the G(1)(nu, Q(2)) sum rule from Q(2) = 0 to infinity.