Nucleon-pion-state contribution to nucleon two-point correlation functions

TL;DR

This paper calculates the nucleon-pion-state contribution to nucleon two-point functions using chiral perturbation theory, finding it to be a small effect at the few percent level, which aids in understanding excited state contamination.

Contribution

It provides the first leading-order calculation of nucleon-pion-state effects on nucleon two-point functions in chiral perturbation theory.

Findings

Nucleon-pion-state contribution is small, at a few percent level.

Both parity channels are analyzed, showing similar small effects.

Results help refine the interpretation of lattice QCD nucleon correlators.

Abstract

We study the nucleon-pion-state contribution to the QCD two-point function of the standard nucleon interpolating fields. For sufficiently small quark masses these two-particle states are expected to have a smaller total energy than the single-particle excited states. We calculate the nucleon-pion-state contribution to leading order in chiral perturbation theory. Both parity channels are considered. We find the nucleon-pion-state contribution to be small, contributing at the few percent level to the effective mass in the positive parity channel.