Nonforward parton distributions

Abstract

Applications of perturbative QCD to deeply virtual Compton scattering and hard exclusive electroproduction processes require a generalization of usual parton distributions for the case when long-distance information is accumulated in nonforward matrix elements $〈p^{\prime }|\mathcal{O}\mathrm{}(0,z)\mathrm{}|p〉$ of quark and gluon light-cone operators. We describe two types of nonperturbative functions parametrizing such matrix elements: double distributions $F(x,y;t)\mathrm{}$ and nonforward distribution functions ${\mathcal{F}}_{\zeta }\mathrm{}(X;t),$ discuss their spectral properties, evolution equations which they satisfy, basic uses and general aspects of factorization for hard exclusive processes.