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We use a generalization of the Rosenbluth separation method for a model independent simultaneous extraction of the Compton Form Factors H and E , from virtual Compton scattering data on an unpolarized target. A precise evaluation of H and E , enabled by the proposed method, is the first step towards pinning down the distribution of angular momentum inside the proton. [ABSTRACT FROM AUTHOR]

We give an interpretation of the u and d quarks contributions to the nucleon electromagnetic form factors for values of the four-momentum transfer in the multi-GeV region where flavor separated data have been recently made available. The data show, in particular, a suppression of d quarks with respect to u quarks at large momentum transfer. This trend can be explained using a reggeized diquark model calculation of generalized parton distributions, thus providing a correlation between momentum and coordinate spaces, both of which are necessary to interpret the partonic substructure of the form factors. We extend our discussion to the second moments of generalized parton distributions which are believed to contribute to partonic angular momentum. [ABSTRACT FROM AUTHOR]

We propose a physically motivated parameterization for the unpolarized generalized parton distributions, H and E, valid at both zero and non-zero values of the skewness variable, ζ. Our approach follows a previous detailed study of the ζ=0 case where H and E were determined using constraints from simultaneous fits of the experimental data on both the nucleon elastic form factors and the deep inelastic structure functions in the non-singlet sector. Additional constraints at ζ≠0 are provided by lattice calculations of the higher moments of generalized parton distributions. We illustrate a method for extracting generalized parton distributions from lattice moments based on a reconstruction using sets of orthogonal polynomials. The inclusion in our fit of data on Deeply Virtual Compton Scattering is also discussed. Our method provides a step towards an extraction of generalized distributions based on a global fit of the available data within the given set of constraints. [ABSTRACT FROM AUTHOR]

The quark-hadron duality is studied in a systematic way for polarized and unpolarized structure functions, by taking into account all the available data in the resonance region. In both cases, a precise perturbative QCD based analysis to the integrals of the structure functions in the resonance region has been done: non perturbative contributions have been disentangled and the higher twist contributions have been evaluated. A different behavior for the unpolarized and polarized structure functions at lowQ2 has been found.PACS:quark-hadron duality - structure functions [ABSTRACT FROM AUTHOR]

We evaluate the impact of recent developments in hadron phenomenology on extracting possible fundamental tensor interactions beyond the standard model. We show that a novel class of observables, including the chiral-odd generalized parton distributions, and the transversity parton distribution function can contribute to the constraints on this quantity. Experimental extractions of the tensor hadronic matrix elements, if sufficiently precise, will provide a, sofar, absent testing ground for lattice QCD calculations. [ABSTRACT FROM AUTHOR]

Abstract: We argue that due to parity constraints, the helicity combination of the purely momentum space counterparts of the Wigner distributions – the generalized transverse momentum distributions – that describes the configuration of an unpolarized quark in a longitudinally polarized nucleon can enter the deeply virtual Compton scattering amplitude only through matrix elements involving a final state interaction. The relevant matrix elements in turn involve light-cone operators projections in the transverse direction, or they appear in the deeply virtual Compton scattering amplitude at twist three. Orbital angular momentum or the spin structure of the nucleon was a major reason for these various distributions and amplitudes to have been introduced. We show that the twist three contributions associated with orbital angular momentum are related to the target-spin asymmetry in deeply virtual Compton scattering, already measured at HERMES. [Copyright &y& Elsevier]

The strong force which binds hadrons is described by the theory of quantum chromodynamics (QCD). Determining the character and manifestations of QCD is one of the most important and challenging outstanding issues necessary for a comprehensive understanding of the structure of hadrons. Within the context of the QCD parton picture, the parton distribution functions (PDFs) have been remarkably successful in describing a wide variety of processes. However, these PDFs have generally been confined to the description of collinear partons within the hadron. New experiments and facilities provide the opportunity to additionally explore the transverse structure of hadrons which is described by generalized parton distributions (GPDs) and transverse-momentum-dependent parton distribution functions (TMD PDFs). In our previous report Lin et al. (2018), we compared and contrasted the two main approaches used to determine the collinear PDFs: the first based on perturbative QCD factorization theorems, and the second based on lattice-QCD calculations. In the present report, we provide an update of recent progress on the collinear PDFs, and also expand the scope to encompass the generalized PDFs (GPDs and TMD PDFs). We review the current state of the various calculations, and consider what new data might be available in the near future. We also examine how a shared effort can foster dialog between the PDF and lattice-QCD communities, and yield improvements for these generalized PDFs. [ABSTRACT FROM AUTHOR]