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Leading and subleading twist transverse momentum dependent parton distribution functions (TMDs) are studied in a quark model framework provided by the bag model. A complete set of relations among different TMDs is derived, and the question is discussed how model-(in)dependent such relations are. A connection of the pretzelosity distribution and quark orbital angular momentum is derived.
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Generalized transverse momentum dependent parton distributions (GTMDs) are the most general parton correlation functions of hadrons. By considering the exclusive double Drell-Yan process it is shown for the first time how quark GTMDs can be measured. Specific GTMDs can be addressed by means of polarization observables.
Transverse momentum dependent parton distribution functions (TMDPDFs) provide a unique probe of the three-dimensional spin structure of hadrons. We construct spin-dependent quasi-TMDPDFs that are amenable to lattice QCD calculations and that can be used to determine spin-dependent TMDPDFs. We calculate the short-distance coefficients connecting spin-dependent TMDPDFs and quasi-TMDPDFs at one-loop order. We find that the helicity and transversity distributions have the same coefficient as the unpolarized TMDPDF. We also argue that the same is true for pretzelosity and that this spin universality of the matching will hold to all orders in $alpha_s$. Thus, it is possible to calculate ratios of these distributions as a function of longitudinal momentum and transverse position utilizing simpler Wilson line paths than have previously been considered.
The Super-Scaling Approach (SuSA) model, based on the analogies between electron and neutrino interactions with nuclei, is reviewed and its application to the description of neutrino-nucleus scattering is presented. The contribution of both one- and two-body relativistic currents is considered. A selection of results is presented where theoretical predictions are compared with cross section measurements from the main ongoing neutrino oscillation experiments.
We develop a non-perturbative model for valence parton distribution functions (PDFs) based on the quark interactions in the mean field of the nucleonic interior. The main motivation for the model is to obtain a mean field description of the valence quarks as a baseline to study the short range quark-quark interactions that generate high $x$ tail of valence quark distributions. The model is based on the separation of valence three-quark system from the residual nucleon system which is the source of the mean field. The nucleon structure function is calculated within effective light-front diagrammatic approach which allows to introduce light-front valence quark and residual wave functions. The model allows us to obtain a new relation between the position of the peak of $xq_V(x)$ distribution of the valence quark and the effective mass of the residual system, $m_R$: $x_{peak} approx {1over 4} (1-{m_Rover m_N})$ and naturally explains the difference in the peak positions for d- and u- quarks due to expected larger residual mass in the case of valence d- quark distribution. The parameters of the model are fixed by fitting the calculated valence quark distributions to the phenomenological parameterizations. This allowed us to estimate the total contribution due to quark-quark correlations which are expected to dominate at high x. The fit allowed also to obtain the $Q^2$ dependence of the mass of the residual system and its effective size which gives a new insight on the effects of the QCD evolution on strongly interacting mean field of the nucleon. Finally, the evaluated parameters of non-perturbative wave functions of valence 3q- and residual system allow them to be used in calculations of other observables such as nucleon form factors, generalized partonic and transverse momentum distributions.
Being the mother distributions of all types of two-parton correlation functions, generalized transverse momentum dependent parton distributions (GTMDs) have attracted a lot of attention over the last years. We argue that exclusive double production of pseudoscalar quarkonia ($eta_c$ or $eta_b$) in nucleon-nucleon collisions gives access to GTMDs of gluons.
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