Partonic quasidistributions in two-dimensional QCD

As a sequel to our preceding work [Y. Jia et al. J. High Energy Phys. 11 (2017) 151], we carry out a comprehensive comparative study between the quasiparton distribution functions (PDFs), distribution amplitudes (DAs), and their light-cone counterparts for various flavor-neutral mesons in the context of the 't Hooft model, that is, the two-dimensional QCD in the large-N limit. In contrast to the original derivation via diagrammatic techniques exemplified by Dyson-Schwinger and Bethe-Salpeter equations, here we employ the Hamiltonian operator approach to reconstruct the celebrated 't Hooft equation in light-front quantization, and Bars-Green equations in equal-time quantization. The novelty of our derivation is to employ the soft momentum cutoff as the IR regulator. As a virtue of this operator approach, the functional form of the quasidistributions can be transparently built out of the Bars-Green wave functions and the Bogoliubov angle with the aid of bosonization technique. Equipped with various bound-state wave functions numerically inferred by Jia et al. [j. High Energy Phys. 11 (2017) 151], we then investigate how rapidly the quasidistributions approach their light-cone counterparts with the increasing meson momentum. We observe that the light mesons' quasidistributions approach the light-cone distributions at a slower pace than the heavy quarkonia. Curiously, lattice simulations of quasidistributions in four-dimensional QCD also discover this feature. Furthermore, we also compute the partonic light-cone PDF and quasi-PDF to one-loop order in perturbation theory, again employing the momentum cutoff as the IR regulator. We explicitly verify one of the backbones underlying the large momentum effective field theory (LaMET), namely, both quasi-PDFs and light-cone PDFs in QCD(2) indeed possess the same IR behavior at leading order in 1/P-z.