Parton Energy Loss in Collinear Expansion
  We demonstrate that the N=1 rescattering contribution to the gluon radiation from a fast massless quark in eA DIS vanishes in the collinear approximation. It is shown that the nonzero N=1 gluon spectrum obtained in the higher-twist approach by Guo, Wang and Zhang is a consequence of unjustified neglecting some important terms in the collinear expansion. 
B.G. Zakharov