Transverse-momentum dependent parton distributions in large-Nc QCD
P. V. Pobylitsa
TL;DR
The paper analyzes transverse-momentum dependent quark distributions (TMDs) in large-$N_c$ QCD with $SU(2)$ isospin, determining the leading twist-2 contributions and their isospin structure, including nonzero T-odd components enabled by Wilson lines. It develops a mean-field description of large-$N_c$ baryons with spin-flavor symmetry, expressing bilocal quark operator matrix elements as collective-coordinate integrals to extract the dominant spin-isospin content. The authors show that $f_1$ and $h_1^{ot}$ are isoscalar at leading order while other spin-dependent TMDs are isovector, and they demonstrate how T-odd distributions arise from $T$-odd Wilson-line structures, not from chiral models lacking Wilson lines. The results provide model-independent, qualitative guidance for real-world QCD and clarify the role of Wilson lines in generating T-odd TMDs within the large-$N_c$ framework.
Abstract
The transverse-momentum dependent quark distributions are studied in the limit of the large number of colors Nc. The leading orders of Nc are determined for all twist-2 distributions including the T-odd functions. The isospin structure of the dominant contributions is found.