Quark and Glue Components of the Proton Spin from Lattice Calculation

TL;DR

This paper reviews lattice QCD calculations of the proton's spin components, highlighting recent advances in determining quark and glue contributions, including the first finite-momentum glue spin calculation.

Contribution

It provides new lattice results for quark and glue spin components, notably the first finite-momentum glue spin calculation, enhancing understanding of proton spin structure.

Findings

Quark spin is small due to the negative anomaly term

First lattice calculation of glue spin at finite momentum

Confirmation of the proton spin crisis from lattice results

Abstract

The status of lattice calculations of the quark spin, the quark orbital angular momentum, the glue angular momentum and glue spin in the nucleon is summarized. The quark spin calculation is recently carried out from the anomalous Ward identity with chiral fermions and is found to be small mainly due to the large negative anomaly term which is believed to be the source of the `proton spin crisis'. We also present the first calculation of the glue spin at finite nucleon momenta.