Nucleon sigma terms with a variational analysis from Lattice QCD

TL;DR

This study uses lattice QCD to accurately determine nucleon sigma terms, highlighting the importance of excited state contamination and demonstrating a method to reduce it using a generalized eigenvector analysis.

Contribution

It introduces a variational analysis approach to reduce excited state contamination in lattice QCD calculations of nucleon sigma terms.

Findings

Excited state contamination mainly from nucleon-sigma scattering states.

Generalized eigenvector analysis reduces excited state effects.

Analysis performed on a single ensemble with unphysical pion mass.

Abstract

We determine the nucleon-sigma terms from lattice QCD. We find that the dominant excited state contamination in the nucleon three-point function with a scalar current is due to the transition between the nucleon and a S-wave scattering state of a nucleon and a scalar (sigma) meson. In this proof-of-concept study, we analyse a single $N_f=3$ ensemble with the unphysically large pion mass $M_\pi=429$ MeV. Excited state contamination is substantially reduced compared to the standard method when employing nucleon-sigma type interpolating operators within a generalised eigenvector analysis.