Nucleon isovector couplings from $N_f=2$ lattice QCD

TL;DR

This study uses lattice QCD simulations with two flavors of fermions to compute nucleon isovector couplings, carefully analyzing systematic effects and extrapolating results to the physical pion mass, achieving agreement with experimental data for most couplings.

Contribution

First lattice QCD calculation of nucleon isovector couplings with non-perturbatively improved Wilson fermions at near-physical pion mass, including systematic analysis and continuum extrapolation.

Findings

Couplings agree with experimental results at physical pion mass.

No significant lattice spacing dependence detected within the studied range.

Finite volume and excited state effects are carefully controlled.

Abstract

We compute the axial, scalar, tensor and pseudoscalar isovector couplings of the nucleon as well as the induced tensor and pseudoscalar charges in lattice simulations with $N_f=2$ mass-degenerate non-perturbatively improved Wilson-Sheikholeslami-Wohlert fermions. The simulations are carried out down to a pion mass of 150 MeV and linear spatial lattice extents of up to 4.6 fm at three different lattice spacings ranging from approximately 0.08 fm to 0.06 fm. Possible excited state contamination is carefully investigated and finite volume effects are studied. The couplings, determined at these lattice spacings, are extrapolated to the physical pion mass. In this limit we find agreement with experimental results, where these exist, with the exception of the magnetic moment. A proper continuum limit could not be performed, due to our limited range of lattice constants, but no significant lattice spacing dependence is detected. Upper limits on discretization effects are estimated and these dominate the error budget.