On gauge invariant nucleon spin decomposition

TL;DR

This paper examines the non-uniqueness of gauge invariant nucleon spin decompositions, proposing criteria to select physically meaningful decompositions consistent with helicity concepts and experimental measurements.

Contribution

It introduces a framework to identify physically relevant gauge invariant nucleon spin decompositions based on helicity and experimental data.

Findings

Multiple gauge invariant decompositions exist, all reducing to the canonical form in specific gauges.

A class of decompositions consistent with helicity and experimental gluon helicity is identified.

The approach clarifies the physical interpretation of nucleon spin components.

Abstract

A non-uniqueness problem of gauge invariant separation of quark and gluon contributions to nucleon spin is considered. We show that there is a wide number of gauge invariant spin decompositions each of them reduces to the canonical one in a special gauge. A class of physical gauge equivalent nucleon spin decompositions is selected by requirements of consistence with helicity notion described within E(2) little group representation theory and with gluon helicity \Delta g measured in experiment.