  A complication in proving factorization theorems in Feynman gauge is that
individual graphs give a super-leading power of the hard scale when all the
gluons inducing the hard scattering are longitudinally polarized. With the aid
of an example in gluon-mediated deep inelastic scattering, we show that,
although the super-leading terms cancel after a sum over graphs, there is a
residual non-zero leading term from longitudinally polarized gluons. This is
due to the non-zero transverse momenta of the gluons in the target. The
non-cancellation, due to the non-Abelian property of the gauge group, is
necessary to obtain the correct form of the gluon distribution function as a
gauge-invariant matrix element.
