Higher twist parton distributions from light-cone wave functions
  We explore the possibility to construct higher-twist parton distributions in a nucleon at some low reference scale from convolution integrals of the light-cone wave functions (WFs). To this end we introduce simple models for the four-particle nucleon WFs involving three valence quarks and a gluon with total orbital momentum zero, and estimate their normalization (WF at the origin) using QCD sum rules. We demonstrate that these WFs provide one with a reasonable description of both polarized and unpolarized gluon parton densities at large values of Bjorken variable x > 0.5. Twist-three parton distributions are then constructed as convolution integrals of qqqg and usual three-quark WFs. The cases of the polarized structure function g_2(x,Q^2) and single transverse spin asymmetries are considered in detail. We find that the so-called gluon-pole contribution to twist-three distributions relevant for single spin asymmetry vanishes in this model, but is generated perturbatively at higher scales by the evolution, in the spirit of GRV parton distributions. 
V.M. Braun, T. Lautenschlager, A.N. Manashov and B. Pirnay
hep-ph