Nucleon-pion-state contribution in lattice calculations of the nucleon charges $g_A,g_T$ and $g_S$

TL;DR

This paper uses covariant chiral perturbation theory to quantify how nucleon-pion states affect lattice QCD calculations of nucleon charges, revealing an overestimation bias in the results.

Contribution

It provides the first detailed estimate of nucleon-pion-state effects on nucleon charge extractions in lattice QCD using chiral perturbation theory.

Findings

Nucleon-pion states cause overestimation of all three charges.

The overestimation is similar for $g_A$ and $g_T$, but larger for $g_S$.

Impacts both plateau and summation methods in lattice calculations.

Abstract

We employ leading order covariant chiral perturbation theory to compute the nucleon-pion-state contribution to the 3-point correlation functions one typically measures in lattice QCD to extract the isovector nucleon charges $g_A,g_T$ and $g_S$. We estimate the impact of the nucleon-pion-state contribution on both the plateau and the summation method for lattice simulations with physical pion masses. The nucleon-pion-state contribution results in an overestimation of all charges with both methods. The overestimation is roughly equal for the axial and the tensor charge, and about fifty percent larger for the scalar charge.