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) eq(x,k⊥) 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 eq(x,k⊥) and the collinear parton distribution eq(x) are presented, discussing the role of the quark–gluon correlations in the proton.