HIGHER-TWIST PARTON DISTRIBUTIONS IN QCD2

The higher-twist structure functions are calculated in QCD1 + 1 and formal sum rules are derived. It is demonstrated that the sum rule for the first moment of f4 is violated if one restricts the integration to "experimental data" (x > 0). However. the sum rule is valid if a delta-function at the origin is taken into account. The physical origin of this delta-function is clarified from the point of view of canonical light-cone quantization ("zero mode" for the "bad" component) as well as using dispersion relations (fixed pole). The coefficient of the delta-function can be calculated by means of these dispersion relations as well as by considering a slightly non-forward Compton amplitude instead of the usual forward amplitude.