Gauge links, TMD-factorization, and TMD-factorization breaking

Abstract

In this section, we discuss some basic features of transverse momentum dependent, or unintegrated, parton distribution functions. In particular, when these correlation functions are combined in a factorization formulae with hard processes beyond the simplest cases, there are basic problems with universality and factorization. We discuss some of these problems as well as the opportunities that they offer.Comment: 9 pages, 10 figures Gluons and the quark sea at high energies: distributions, polarization, tomograph