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 δ-function at the origin is taken into account. The physical origin of this δ-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 δ-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. (orig.)