Factorization of soft and collinear divergences in QCD in the Feynman gauge via a background field gauge
We prove Ward-type identities which are needed in the proof of factorization of the Drell-Yan process. Previous treatments prove them only for an axial gauge, and the proofs are diagrammatic in nature. We, on the other hand, establish the identities for the Feynman gauge and through symmetry considerations at the Lagrangian level. Our strategy is to first derive exact results in a background field gauge and then to show that to leading order in the mass divergences the background-field-gauge results can be used in the Feynman gauge.