Direct Evaluation of the Quark Content of Nucleons from Lattice QCD at the Physical Point

TL;DR

This study uses lattice QCD to accurately evaluate the scalar quark content of nucleons, including light, strange, and charm quarks, providing key insights into nucleon structure at the physical point.

Contribution

It introduces improved techniques for calculating disconnected quark loops, enabling precise determination of strange and charm sigma-terms in nucleons from lattice QCD.

Findings

Nucleon sigma-term for pions: 37.2 MeV

Nucleon strange sigma-term: 41.1 MeV

Nucleon charm sigma-term: 79 MeV

Abstract

We evaluate the light, strange and charm scalar content of the nucleon using one lattice QCD ensemble generated with two degenerate light quarks with mass fixed to their physical value. We use improved techniques to evaluate the disconnected quark loops to sufficient accuracy to determine the strange and charm nucleon $\sigma$-terms. in addition to the light quark content $\sigma_{\pi N}$. We find $\sigma_{\pi N}$=$37.2(2.6)(^{4.7}_{2.9})$ MeV $\sigma_{s}$=$41.1(8.2)(^{7.8}_{5.8})$ MeV and $\sigma_c$=$79(21)(^{12}_{\phantom{1}8})$ MeV, where the first error is statistical and the second is the systematic error due to the determination of the lattice spacing, the assessment of finite volume and residual excited state effects.