Parton distribution functions for twist 4

All O(1/Q2) corrections to leptoproduction are described by a small number of generalized multiparton distribution functions which depend only on the longitudinal momentum of the partons. We show that these functions can be represented (in A+=0 gauge) by sequential emission or absorption by the target of quarks, antiquarks and gluons where (I) all quanta move with O<=k+/p+<=1; (II) all intermediate hadronic states are on-mass-shell; (III) no graphs are semi-disconnected with respect to the target or the intermediate hadronic state. We show how all O(1/Q2) corrections to the forward virtual Compton amplitude can be represented in terms of these parton distributions. (orig.)