Improved Parton Distribution Functions at Physical Pion Mass

TL;DR

This paper reports the first lattice QCD calculations of isovector unpolarized and polarized PDFs at physical pion mass using LaMET, addressing renormalization challenges and proposing solutions to unphysical oscillations in the data.

Contribution

It introduces methods to mitigate unphysical oscillations in renormalized quasi-PDFs, enabling more accurate lattice determinations of PDFs at physical pion mass.

Findings

Successful nonperturbative renormalization of quasi-PDFs.

Proposed solutions effectively reduce unphysical oscillations.

Demonstrated methods on 2+1+1-flavor lattice data at physical pion mass.

Abstract

We present the first lattice results on isovector unpolarized and longitudinally polarized parton distribution functions (PDFs) at physical pion mass. The PDFs are obtained using the large-momentum effective field theory (LaMET) framework where the full Bjorken-$x$ dependence of finite-momentum PDFs, called "quasi-PDFs", can be calculated on the lattice. The quasi-PDF nucleon matrix elements are renormalized nonperturbatively in RI/MOM-scheme. However, the recent renormalized quasi-PDFs suffer from unphysical oscillations that alter the shape of the true distribution as a function of Bjorken-$x$. In this paper, we propose two possible solutions to overcome this problem, and demonstrate the efficacy of the methods on the 2+1+1-flavor lattice data at physical pion mass with lattice spacing 0.09~fm and volume $(5.76\mbox{ fm})^3$.