Chiral-even twist-3 GPDs for the proton in a spectator diquark model

Abstract

We investigate the chiral-even twist-3 generalized parton distributions (GPDs) of valence quarks in the proton at nonzero skewness $\xi$, using a spectator model with scalar and axial-vector diquarks. We consider the exponential form factor for the nucleon-quark-diquark vertex and the axial-vector diquark with light-cone transverse polarization. We analyze the dependence of GPDs on the longitudinal momentum fraction $x$ at different $\xi$, and on the square of the transverse momentum transfer ${\Delta }_T^2$ at different $x$. Our numerical results reveal distinct discontinuities in all twist-3 GPDs except $G_1$ and ${\tilde{G}}_1$. By taking the forward limit, we obtain the twist-3 parton distribution function $g_T$, which encodes the transverse spin distribution of quarks. We also compare the kinetic orbital angular momentum and the spin-orbit correlations of quarks defined by the twist-2 and twist-3 GPDs, respectively.

Comments: 18 pages, 8 figures