Partonic Picture of Generalized Transverse Momentum Distributions

Understand

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 twist three contributions to deeply virtual Compton scattering provide observables related to orbital angular momentum.