# The strange quark contribution to the spin of the nucleon

## TL;DR

This paper presents a novel lattice QCD method using the Feynman-Hellmann theorem to efficiently compute the strange quark's contribution to the nucleon spin, addressing noise issues in traditional stochastic estimators.

## Contribution

The authors develop and apply an alternative Feynman-Hellmann based approach for calculating disconnected matrix elements, improving accuracy for strange quark spin contributions.

## Key findings

- Successful computation of strange quark spin contribution to the nucleon.
- Development of an SU(3) flavour breaking expansion for singlet operators.
- Enhanced precision in lattice QCD calculations of disconnected diagrams.

## Abstract

Quark line disconnected matrix elements of an operator, such as the axial current, are difficult to compute on the lattice. The standard method uses a stochastic estimator of the operator, which is generally very noisy. We discuss and develop further our alternative approach using the Feynman-Hellmann theorem which involves only evaluating two-point correlation functions. This is applied to computing the contribution of the quark spin to the nucleon and in particular for the strange quark. In this process we also pay particular attention to the development of an SU(3) flavour breaking expansion for singlet operators.