  QCD factorization takes different forms in the large-x and small-x regimes.
At large-x, collinear factorization leads to the DGLAP evolution equation,
while at small-x, rapidity factorization results in the BFKL equation. To unify
these different regimes, a new TMD factorization based on the background field
method is proposed. This factorization not only reduces to CSS and DGLAP in the
large-x limit and BFKL in the small-x limit, but also defines a general
evolution away from these regimes.
