Mass corrections in deep-inelastic scattering

The moment sum rules for deep-inelastic lepton scattering are expected for asymptotically free field theories to display a characteristic pattern of logarithmic departures from scaling at large enough Q². In the large-Q² limit these patterns do not depend on hadron or quark masses m. For modest values of Q² one expects corrections at the level of powers of m²Q². We discuss the question whether these mass effects are accessible in perturbation theory, as applied to the twist-2 Wilson coefficients and more generally. Our conclusion is that some part of the mass effects must arise from a nonperturbative origin. We also discuss the corrections which arise from higher orders in perturbation theory for very large Q², where mass effects can perhaps be ignored. The emphasis here is on a characterization of the Q², x domain where higher-order corrections are likely to be unimportant.