These proceedings contain the 'physical' derivation of the Wandzura-Wilczek relations for the spin-dependent structure function g2 (amounting to keeping the intrinsic transverse momentum of quarks, and neglecting the physical transverse components of the gluon fields), recently generalized for the case of non-forward processes (hep-ph/0102209). The simple numerical model for the twist-3 contribution to g2 was also suggested.
@article{arxiv.hep-ph/0102296,
title = {Twist-3 in Proton Nucleon Single Spin Asymmetries},
author = {O. V. Teryaev},
journal= {arXiv preprint arXiv:hep-ph/0102296},
year = {2007}
}