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 ρ−meson, based on recent calculation of the γ∗ T → ρT impact factor up to twist 3 accuracy in the collinear factorization frame, including 2and 3particles 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 (γ∗ T → ρT )/T (γ∗ L → ρL) and T (γ∗ T → ρL)/T (γ∗ L → ρL). In the second approach, we transform the γ∗ T → ρT 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.