Decomposition of non-local light-cone operators into harmonic operators ofdefinite twist

Bilocal light-ray operators which are Lorentz scalars, vectors or antisymme tric tensors, and which appear in various hard QCD scattering processes, ar e decomposed into operators of definite twist. These operators are harmonic tensor functions and their Taylor expansion consists of (traceless) local light-cone operators which span irreducible representations of the Lorentz group with definite spin j and common (geometric) twist (= dimension - spin ). Some applications concerning the non-forward matrix elements of these op erators and the generalization to conformal light-cone operators of definit e twist is considered. The group theoretical background of the method has b een made clear. (C) 1999 Elsevier Science B.V. All rights reserved.