Gluon distribution function and factorization in Feynman gauge

A complication in proving factorization theorems in Feynman gauge is that individual graphs give a superleading 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 superleading terms cancel after a sum over graphs, there is a residual nonzero leading term from longitudinally polarized gluons. This is due to the nonzero transverse momenta of the gluons in the target. The noncancellation, 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.