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

We introduce a group theoretically motivated procedure of parametrizing non-forward matrix elements of non-local QCD operators by (two-variable) distribution amplitudes of well-defined geometric twist being multiplied by kinematical factors (related to the Lorentz structure of the operators and to the target states) as well as position-dependent coefficient functions resulting from the (infinite) twist decomposition of the operators. These distribution amplitudes are interpreted as (sum over) power corrections of the double distributions. Using the technique of harmonic polynomials for the local operators we determine the (infinite) twist decomposition of totally symmetric operators completely and for operators with non-trivial symmetry type up to twist τ=3. This covers the phenomenological interesting quark–antiquark 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 obtained, by harmonic extension, from the corresponding expressions for operators or distribution amplitudes, on the light-cone.