Gauge invariance and renormalization-group effects in transverse-momentum dependent parton distribution functions

A range of issues pertaining to the use of Wilson lines in integrated and transverse-momentum dependent (TMD) parton distribution functions (PDF) is discussed. The relation between gauge invariance and the renormalization properties of the Wilson-line integrals is given particular attention. Using an anomalous-dimensions based analysis in the light-cone gauge, a generalized definition of the TMD PDFs is proposed, which employs a cusped Wilson line, and contains an intrinsic “Coulomb-like” phase.