More on the relation between the two physically inequivalent decompositions of the nucleon spin

TL;DR

This paper clarifies that only two gauge-invariant decompositions of the nucleon spin are physically inequivalent, addressing a controversy in the QCD spin physics community.

Contribution

It provides a critical overview demonstrating the existence of exactly two physically inequivalent gauge-invariant nucleon spin decompositions.

Findings

Only two gauge-invariant decompositions are physically inequivalent.

The view of infinitely many decompositions is incorrect.

Clarifies the theoretical foundation of nucleon spin structure.

Abstract

The recent controversy on the nucleon spin decomposition problem is critically overviewed. We argue that there exist two and only two physically inequivalent gauge-invariant decompositions of the longitudinal nucleon spin, contrary to the rapidly spreading view in the QCD spin physics community that there are infinitely many decompositions of the nucleon spin.