Nucleon-pion-state contributions in the determination of the nucleon axial charge

TL;DR

This paper investigates how nucleon-pion states affect the calculation of the nucleon axial charge using chiral perturbation theory, finding their contribution to be small but relevant for precise measurements.

Contribution

It provides a leading-order chiral perturbation theory analysis of nucleon-pion-state effects on axial charge calculations, independent of low-energy constants.

Findings

Nucleon-pion states contribute at a few percent level.

Results are independent of low-energy constants at leading order.

Applicable to both local and smeared interpolators.

Abstract

The nucleon-pion-state contributions to QCD 2- and 3-point functions used in the calculation of the nucleon axial charge are studied in chiral perturbation theory. For sufficiently small quark masses and large volumes the nucleon-pion states are expected to have smaller total energy than the single-particle excited states. To leading order in chiral perturbation theory the results do not depend on low-energy constants associated with the interpolating nucleon fields and apply to local as well as smeared interpolators. The nucleon-pion-state contribution is found to be at the few percent level.