Power corrections of off-forward quark distributions and harmonic operators with definite geometric twist

We introduce a group theoretically motivated procedure of parametrizing non -forward matrix elements of non-local QCD operators by (two-variable) distr ibution amplitudes of well-defined geometric twist being multiplied by kine matical factors (related to the Lorentz structure of the operators and to t he target states) as well as position-dependent coefficient functions resul ting from the (infinite) twist decomposition of the operators. These distri bution amplitudes are interpreted as (sum over) power corrections of the do uble distributions. Using the technique of harmonic polynomials for the loc al operators we determine the (infinite) twist decomposition of totally sym metric operators completely and for operators with non-trivial symmetry typ e up to twist tau = 3. This covers the phenomenological interesting quark-a ntiquark operators. Using these results we determine the power corrections to the various double distributions and the vector meson wave functions. It is shown that the structure of the kinematical power corrections may be ob tained, by harmonic extension, from the corresponding expressions for opera tors or distribution amplitudes, on the light-cone. (C) 2001 Elsevier Scien ce B.V. All fights reserved.