Theory of transverse-momentum parton densities: solving the puzzle of divergences

Abstract

The current status of the theoretical understanding of the transverse-momentum dependent parton densities (TMDs) is discussed. Special attention is payed to the difference between the operator definitions of TMDs proposed so far, the treatment of specific divergences, the geometry of the gauge links, and the role of the soft factors.

Comments: 6 pages, 1 figure. Invited talk presented at the 40th International Symposium on Multiparticle Dynamics, 21 - 25 Sep 2010, Antwerp (Belgium)