Twist decomposition of nonlocal light-cone operators II: general tensors of 2nd rank

A group theoretical procedure, introduced earlier in [20,21], to decompose bilocal light-ray operators into (harmonic) operators of definite twist is applied to the case of arbitrary 2nd rank tensors. As a generic example the biloc al gluon operator is considered which gets contributions of twist-2 up to twist-6 from four different symmetry classes characterized by corresp onding Young tableaux; also the twist decomposition of the related vector a nd scalar operators is considered. In addition, we extend these results to various trilocal light-ray operators, like the Shuryak-Vainshtein, the thre e-gluon and the four-quark operators, which are required for the considerat ion of higher-twist distribution amplitudes. The present results rely on th e knowledge of harmonic tensor polynomials of any order n which have been d etermined up to the case of 2nd rank symmetric tensor for arbitrary space-t ime dimension. (C) 2000 Elsevier Science B.V. All rights reserved.