Nucleon structure functions from dynamical (2+1)-flavor domain wall fermions

TL;DR

This study demonstrates that low moments of nucleon structure functions from (2+1)-flavor domain-wall fermion lattice QCD are independent of lattice volume and align well with experimental data, highlighting minimal finite-size effects.

Contribution

The paper provides the first evidence of volume independence for certain nucleon structure function moments in dynamical lattice QCD with domain-wall fermions.

Findings

Low moments are volume independent within statistical errors.

The ratio of moments matches experimental values and is unaffected by finite-size effects.

Absolute values trend towards experimental results at lighter quark masses.

Abstract

We report lattice-volume independence of low moments of nucleon structure functions from the coarse RIKEN-BNL-Columbia (RBC) and UKQCD joint dynamical (2+1)-flavor domain-wall fermions (DWF) ensembles at the lattice cut off of (a^{-1}\sim1.7) GeV. The isovector quark momentum fraction, (< x >_{u-d}), and helicity fraction, (< x >_{\Delta u - \Delta d}), both fully non-perturbatively renormalized are studied on two spatial volumes of ((\sim {\rm 2.7 fm})^3) and ((\sim {\rm 1.8 fm})^3). Their naturally renormalized ratio, (< x >_{u-d}/< x >_{\Delta u - \Delta d}), is not affected by any finite-size effect. It does not depend strongly on light quark mass and does agree well with the experiment. The respective absolute values, fully non-perturbatively renormalized, do not show any finite-size effect either. They show trending toward the respective experimental values at the lightest up- and down-quark mass. This trending down to the experimental values appears to be a real physical effect driven by lighter quarks. The observations are in contrast to the huge finite-size effect seen in the axial-current form factors.