  It has been suggested that under certain approximations the Sivers effect can
be described in terms of factorization of final state interactions and a
spatial distortion of impact parameter space parton distribution; that is a
convolution of the so-called lensing function and the impact parameter GPD $E$.
In this approach the lensing function is calculated in a non-perturbative
eikonal model. This enables a comparison between the a priori distinct Sivers
function and the GPD $E$ which goes beyond the discussion of overall signs.

High Energy Physics - Phenomenology