# New Developments in Lattice QCD: Calculation of Flavor Singlet Nucleon Matrix Elements and Hadron Scattering Lengths

## TL;DR

This paper reviews recent advances in lattice QCD calculations of flavor singlet nucleon matrix elements and hadron scattering lengths, highlighting significant sea quark contributions and discussing current challenges.

## Contribution

It presents new lattice QCD results on flavor singlet matrix elements and hadron scattering lengths, emphasizing the role of sea quarks and addressing existing issues.

## Key findings

- Sea quark contributions are substantial in the $ ext{π-N σ}$ term.
- Total nucleon quark spin content aligns with experimental data.
- Problems remain with flavor non-singlet nucleon matrix elements.

## Abstract

Recent developments in lattice QCD calculation of flavor singlet nucleon matrix elements are reviewed. Substantial sea quark contributions are found in the $\pi$-$N\ \sigma$ term and the quark spin content of the nucleon such that the total magnitude including valence contributions is in reasonable agreement with experiments. Some problems with flavor non-singlet nucleon matrix elements are pointed out. Recent work on lattice QCD calculation of hadron scattering length is also discussed.