Hadronic structure on the light-front VII. Pions and kaons and their partonic distributions

TL;DR

This paper develops a light-front quark model for pions and kaons, deriving their partonic distributions and showing consistency with lattice QCD and experimental data, emphasizing the role of chiral symmetry breaking and instanton effects.

Contribution

It introduces a light-front approach to hadronic structure that incorporates instanton-induced chiral symmetry breaking, deriving meson distribution amplitudes and PDFs consistent with other QCD frameworks.

Findings

Derived light front distribution amplitudes and PDFs for pions and kaons.

Found good agreement with lattice QCD and experimental measurements.

Demonstrated the role of instantons in chiral symmetry breaking on the light front.

Abstract

This work is a continuation in our series of papers, that addresses quark models of hadronic structure on the light front, motivated by the QCD vacuum structure and lattice results. The spontaneous breaking of chiral symmetry on the light front, is shown to parallel that in the rest frame, where the non-local instanton induced $^\prime$t Hooft interaction plays a central role. By rewriting this interaction solely in terms of the good component of the fermionic field, a scalar chiral condensate emerges in the mean-field approximation, which is identical to the one obtained in the rest frame. The pions and kaons emerge as deeply bound Goldstone modes in the chiral limit, with the scalar-isoscalar sigma meson mode as a threshold state with zero binding. We explicitly derive the light front distribution amplitudes (DAs) and partonic functions (PDFs) for these mesons. The DAs and PDFs are in good agreement with those extracted from the QCD instanton vacuum in the rest frame, using the large momentum effective theory (LaMET). The QCD evolved DAs and PDFs compare well with available measurements, as well as recent lattice results.