Systematic Study of the Self-Renormalized Nucleon Gluon PDF in Large-Momentum Effective Theory

TL;DR

This paper systematically investigates the nucleon gluon PDF using self-renormalized LaMET in lattice QCD, addressing key systematic effects and demonstrating the method's effectiveness for future high-precision QCD studies.

Contribution

It introduces a self-renormalization framework for gluon PDFs in lattice QCD, improving control over systematic uncertainties and extending calculations to higher nucleon momenta.

Findings

Smearing and lattice-spacing effects are well-controlled.

Pion-mass and lattice-spacing dependence are mild.

Momentum dependence remains a significant uncertainty.

Abstract

We present a systematic study of the nucleon gluon parton distribution function (PDF) using the self-renormalized large-momentum effective theory (LaMET) approach in lattice QCD. This work extends previous gluon-PDF extractions by performing a detailed analysis of key systematic effects, including gauge-link smearing, lattice spacing, pion mass, and nucleon boost momentum. The self-renormalization framework mitigates ultraviolet divergences associated with Wilson-line self-energy and renormalon contributions by combining lattice matrix elements with perturbative short-distance information, thereby preserving the correct infrared structure. Calculations are performed on $N_f=2+1+1$ HISQ ensembles generated by the MILC Collaboration at three lattice spacings and two pion masses, with boosted nucleon states reaching momenta up to 2.2~GeV. We determine renormalization factors from zero-momentum matrix elements and apply hybrid renormalization to suppress discretization artifacts. After extrapolating large-separation behavior and performing Fourier transforms, we reconstruct quasi-PDFs and match them to lightcone PDFs using next-to-leading order Wilson coefficients. Our results demonstrate that smearing and lattice-spacing effects are under control, and pion-mass and lattice-spacing dependence is mild relative to the current $O(10^6)$ statistics; however, momentum dependence remains a significant source of uncertainty. Future work including even larger boost momenta will be essential to reduce systematics in lattice determinations of the gluon PDF and to advance toward precision QCD phenomenology at the LHC and the future Electron-Ion Collider.