N -> Delta DVCS, exclusive DIS processes and skewed quark distributions in large N_c limit

Abstract

We evaluate the amplitude of Bethe-Heitler process: \gamma^* p -> \gamma \Delta^+ -electron bremsstrahlung of photon accompanied by the excitation of \Delta$ isobar. We show that this background is suppressed at small momentum transfer squared t to a proton relative to that for \gamma^* p -> \gamma p and \gamma^* p\to -> \Delta^+ - DVCS processes. From experimental point of view, this means that N -> N and N -> \Delta skewed quark distributions (SQD's) might be measurable at small momentum transfer. Several implications and applications of the QCD factorization theorem for the processes \gamma_{L}^* + p -> h_f +h_s are discussed where h_f - the particle produced along photon momentum $\vec q$ maybe either a meson or a baryon. We discuss also t dependence of DVCS and exclusive meson production as the practical criteria to distinguish between soft and hard regime. Basing on the large-N_c picture of the nucleon as a soliton of the effective chiral Lagrangian we derive relations between N -> N and N ->\Delta SQD's which can be used to estimate amplitude of N -> \Delta DVCS .