Twist-2 Generalized TMDs and the Spin/Orbital Structure of the Nucleon
K. Kanazawa, C. Lorcé, A. Metz, B. Pasquini, M. Schlegel
TL;DR
The paper defends the existence and twist-2 nature of the GTMDs $F_{1,4}$ and $G_{1,1}$, linking them to parton orbital angular momentum and spin–orbit correlations in the nucleon. It supports this with model calculations in a scalar diquark and a quark-target framework and with perturbative QCD at large transverse momentum, showing these GTMDs are nonzero and physically meaningful. It also refutes the two-body scattering argument that claimed these GTMDs cannot exist at twist-2, clarifying parity properties and the role of Wilson-line phases, and highlighting the real, impact-parameter space content connected to OAM via Wigner and overlap representations. Overall, the work solidifies F_{1,4} and G_{1,1} as essential elements in a complete three-dimensional description of nucleon structure and OAM decomposition.
Abstract
Generalized transverse-momentum dependent parton distributions (GTMDs) encode the most general parton structure of hadrons. Here we focus on two twist-2 GTMDs which are denoted by $F_{1,4}$ and $G_{1,1}$ in parts of the literature. As already shown previously, both GTMDs have a close relation to orbital angular momentum of partons inside a hadron. However, recently even the mere existence of $F_{1,4}$ and $G_{1,1}$ has been doubted. We explain why this claim does not hold. We support our model-independent considerations by calculating the two GTMDs in the scalar diquark model and in the quark-target model, where we also explicitly check the relation to orbital angular momentum. In addition, we compute $F_{1,4}$ and $G_{1,1}$ at large transverse momentum in perturbative Quantum Chromodynamics and show that they are nonzero.