Transverse-momentum-dependent parton distributions at the edge of the lightcone

Abstract

We present a completely gauge-invariant operator definition of transverse-momentum-dependent parton densities (TMD), supplied with longitudinal lightlike gauge links as well as transverse gauge links at lightcone infinity. Within this framework, we consider the consistent treatment of specific divergences, emerging in the "unsubtracted" TMD beyond the tree approximation, and construct the soft factors to cancel unphysical singularities. We confront this approach with factorization schemes, which make use of covariant gauges with off-the-lightcone gauge links, and discuss their mutual connection.

Comments: 10 pages, 2 figures; needs ws-ijmpcs.cls (supplied). Invited talk presented at Workshop "QCD evolution of parton distributions: from collinear to non-collinear case", 8 - 9 Apr 2011, Thomas Jefferson National Accelerator Facility, Newport News (VA), USA