Theory and phenomenology of helicity amplitudes for high energy exclusive leptoproduction of the rho-meson

We review here two approaches to describe hard leptoproduction of transversally polarized rho-meson, based on recent calculation of the gammaT -> rhoT impact factor up to twist 3 accuracy in the collinear factorization frame, including 2- and 3- particles Fock-states. The first approach uses a model of the unintegrated gluon density (the proton impact factor) which allows a comparison of our predictions with H1 and ZEUS data for the ratios of helicity amplitudes T(gammaT -> rhoT)/T(gammaL -> rhoL) and T(gammaT -> rhoL)/T(gammaL -> rhoL). In the second approach, we transform the gammaT -> rhoT impact factor into the impact parameter space. We show that the transformed amplitude factorizes according to conventional dipole picture. We shortly discuss a way to implement the nucleon saturation effects in our approach.