Virtual Compton scattering off the nucleon

Abstract

We review the recent developments of virtual Compton scattering. We focus on the kinematical regimes which look the most promising. The threshold regime gives access to the generalized polarizabilities of the proton. The hard scattering regime allows tests of perturbative QCD predictions and of the valence quark wave function. The Bjorken regime is closely related to deep inelastic scattering. It gives access to the off-forward parton distributions which generalize the ordinary parton distributions and may shed a new light on the spin problem. For each regime we discuss the experimental perspectives and the role of the Bethe-Heitler background.

New contributions to gluon poles in direct photon production

“…The twist-3 quark distribution which appears in the diagrams D1-D4 presented in Fig. 3 is given by (1) …”

“…The problem of the electromagnetic (QED) gauge invariance in the deeply virtual Compton scattering and similar exclusive processes has intensively been discussed during the last few years (for example, see [1][2][3][4][5][6]). This development explored the similarity with the earlier studied inclusive spin-dependent processes [7].…”

Kinematical Issues in the GPD Formulation of DVCS

“…In our more general kinematics K 4 we thus find for T s (see also Vanderhaegen et al [6][7][8][9][10][11] where transversemomentum components are included)…”

“…The inclusion of higher twist effects [6][7][8][9][10][11]15] is at the current forefront of research and it may well go beyond the handbag approximation.…”

Wandzura–Wilczek approximation from generalized rotational invariance

“…Indeed, these corrections ensure the electromagnetic gauge invariance of the DVCS amplitude with the sizeable transverse components of the momentum transfer. This problem was discussed in the pioneering paper [1] and the phenomenological solution was presented in [2]. The field-theoretical treatment was suggested in [3,4] and developed in [5,6,7].…”