Generalized parton distributions of gluon in proton: a light-front quantization approach

TL;DR

This paper calculates gluon generalized parton distributions in the proton using light-front quantization, revealing how gluon transverse size varies with momentum fraction and contributing to understanding proton spin structure.

Contribution

It introduces a novel light-front quantization approach to compute gluon GPDs, including dynamical gluons, within a basis light-front framework.

Findings

Gluon transverse size is larger at low-x than at high-x.

The gluon contributes significantly to the proton's total angular momentum.

The approach incorporates both valence and gluonic Fock sectors.

Abstract

We solve for the gluon generalized parton distributions (GPDs) inside the proton, focusing specifically on leading twist chiral-even GPDs. We obtain and employ the light-front wavefunctions (LFWFs) of the proton from a light-front quantized Hamiltonian with Quantum Chromodynamics input using basis light-front quantization (BLFQ). Our investigation incorporates the valence Fock sector with three constituent quarks and an additional Fock sector, encompassing three quarks and a dynamical gluon. We examine the GPDs within impact parameter space and evaluate the $x$-dependence of the transverse square radius. We find that the transverse size of the gluon at lower-$x$ is larger than that of the quark, while it exhibits opposite behavior at large-$x$. Using the proton spin sum rule, we also determine the relative contributions of quarks and the gluon to the total angular momentum of the proton.