The twist-three distribution eq(x, k⊥) in a light-front model

We discuss the twist-three, unpolarized, chiral-odd, transverse momentum dependent parton distribution (TMD) e(q)(x, k(perpendicular to)) within a light-front model. We review a model-independent decomposition of this TMD, which follows from the QCD equations of motion and is given in terms of a mass term, a pure interaction-dependent contribution, and singular terms. The mass-term and pure twist-three contributions are represented in terms of overlap of light-front wave functions (LFWFs), taking into account the Fock states with three valence quark (3q) and three-quark plus one gluon (3q+g). The 3q and 3q+g LFWFs with total orbital angular momentum zero are modeled using a parametrization derived from the conformal expansion of the proton distribution amplitudes, with parameters fitted to reproduce available phenomenological information on the unpolarized leading-twist quark and gluon collinear parton distributions. Numerical predictions for both the quark TMD e(q)(x, k(perpendicular to)) and the collinear parton distribution e(q)(x) are presented, discussing the role of the quark-gluon correlations in the proton. (C) 2018 The Author(s). Published by Elsevier B.V.