Transverse-Distance Dependent Parton Densities in the Large-xx Regime

QCD factorization approach in the field-theoretic description of the semi-inclusive hadronic processes in the large Bjorken $x$ approximation implies extraction of the three-dimensional parton distribution functions as a convolution of a collinear jet function and soft transverse-distance dependent (TDD) function defined as a vacuum average of a partially light-like Wilson loop. The soft function can be interpreted, therefore, as an element of generalized loop space. A class of classically conformal-invariant transformations of the elements of this space is generated by the non-local area derivative operator which corresponds to a diffeomorphism in the loop space and determines equations of motion, the latter being associated with the rapidity evolution of the soft TDD functions. We propose a large-$x$ TDD factorization framework and discuss practical applications of this approach to the phenomenology of the TDDs accessible in future experimental programs at the Jefferson Lab 12 GeV and the Electron-Ion Collider.Comment: 6 pages; based on invited talk presented at "Lightcone 2013+: Venturing off the LightCone - Local vs. Global Features", Skiathos, Greece, 20-24 May 2013; submitted to Few Body System

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

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

Taming singularities in transverse-momentum-dependent parton densities

We propose a consistent treatment of divergences emerging in the computation of transverse-momentum-dependent parton densities in leading $\alpha_s$-order of QCD perturbation theory.Comment: 3 pages, 1 figure. Talk presented at the International Workshop on Diffraction in High-Energy Physics, 10-15 Sept, 2010, Otranto (Lecce), Italy. v2: affiliation and references correcte