Spin-flavor structure of chiral-odd GPDs in the large-N_c limit

TL;DR

This paper analyzes the spin-flavor structure of chiral-odd generalized parton distributions (GPDs) in nucleons using the large-N_c limit of QCD, revealing specific non-zero combinations and their flavor dependencies, consistent with experimental data.

Contribution

It identifies the leading combinations of chiral-odd GPDs in the large-N_c limit and explains their flavor and spin-flavor structure, providing new theoretical insights into nucleon structure.

Findings

Only three combinations of chiral-odd GPDs are non-zero at leading order in 1/N_c.

Flavor-singlet u+d dominates in E_T-bar, while u-d dominates in H_T and E_T-tilde.

Large-N_c relations align with experimental data from pi0 and eta electroproduction.

Abstract

We study the spin-flavor structure of the nucleon's chiral-odd generalized parton distributions (transversity GPDs) in the large-N_c limit of QCD. In contrast to the chiral-even case, only three combinations of the four chiral-odd GPDs are non-zero in the leading order of the 1/N_c expansion: E_T-bar = E_T + 2 H_T-tilde, H_T and E_T-tilde. The degeneracy is explained by the absence of spin-orbit interactions correlating the transverse momentum transfer with the transverse quark spin. It can also be deduced from the natural N_c-scaling of the quark-nucleon helicity amplitudes associated with the GPDs. In the GPD E_T-bar the flavor-singlet component u + d is leading in the 1/N_c expansion, while in H_T and E_T-tilde it is the flavor-nonsinglet components u - d. The large-N_c relations are consistent with the spin-flavor structure extracted from hard exclusive pi0 and eta electroproduction data, if it is assumed that the processes are mediated by twist-3 amplitudes involving the chiral-odd GPDs and the chiral-odd pseudoscalar meson distribution amplitudes.