EXCLUSIVE LEPTOPRODUCTION OF A LIGHT VECTOR MESON AT THE TWIST-3 IN A GTMD FRAMEWORK

We provide the most general description of the exclusive leptoproduction of a light vector meson at high center-of-mass energy, within the CGC/shockwave formalism. We keep a twist-3 accuracy in the s channel, thus being able to describe all possible helicity amplitudes, including the ones for the production of a transversally polarized meson. In this latter case, we overcome the well-known issue of endpoint singularities by promoting the GPD to a GTMD given by matrix elements of dipole and double-dipole operators. The all-twist treatment of the proton (nucleon) target allows to safely twist-expand the general vacuum-to-meson matrix elements. Therefore, unlike previous attempts in the modified perturbative approach, our final results are expressed in terms of the twist-3 collinear distribution amplitudes, introduced in the context of the higher-twist collinear formalism.