Gauge- and frame-independent decomposition of nucleon spin

TL;DR

This paper establishes a gauge- and frame-independent decomposition of the nucleon spin, demonstrating its observability in high-energy experiments and its reflection of an intrinsic nucleon property.

Contribution

It provides a fully gauge- and Lorentz frame-independent decomposition of nucleon spin, linking it to observable quantities in high-energy scattering.

Findings

The decomposition corresponds to measurable quantities in deep-inelastic scattering.

It is gauge-invariant and Lorentz frame-independent.

The approach reflects an intrinsic property of the nucleon.

Abstract

In a recent paper, we have shown that the way of gauge-invariant decomposition of the nucleon spin is not necessarily unique, but there still exists a preferable decomposition from the observational viewpoint. What was not complete in this argument is a fully satisfactory answer to the following questions. Does the proposed gauge-invariant decomposition, especially the decomposition of the gluon total angular momentum into its spin and orbital parts, correspond to observables which can be extracted from high-energy deep-inelastic-scattering measurements ? Is this decomposition not only gauge-invariant but also Lorentz frame-independent, so that it is legitimately thought to reflect an intrinsic property of the nucleon ? We show that we can answer both of these questions affirmatively, by making full use of a gauge-invariant decomposition of covariant angular momentum tensor of QCD in an arbitrary Lorentz frame.