On the two remaning issues in the gauge-invariant decomposition problem of the nucleon spin

Abstract

The question whether the total gluon angular momentum in the nucleon can be decomposed into its spin and orbital parts without conflict with the gauge-invariance principle has been an object of long-lasting debate. Despite a remarkable progress achieved through the recent intensive researches, the following two issues still remains to be clarified more transparently. The first issue is to resolve the apparent conflict between the proposed gauge-invariant decomposition of the total gluon angular momentum and the textbook statement that the total angular momentum of the photon cannot be gauge-invariantly decomposed into its spin and orbital parts. We show that this problem is also inseparably connected with the uniqueness or non-uniqueness problem of the nucleon spin decomposition. The second practically more important issue is that, among the two physically inequivalent decompositions of the nucleon spin, i.e. the "canonical" type decomposition and the "mechanical" type decomposition, which can we say is more physical or closer to direct observation ? In the present paper, we try to answer both these questions as clearly as possible.

The version to appear in European Physical Journal A

References in corpus (12)

• Angular Momenta and Spin-Orbit Interaction of Nonparaxial Light in Free Space
• Generalized parton correlation functions for a spin-1/2 hadron
• Quark Wigner Distributions and Orbital Angular Momentum
• Reply to the Comment on "Spin and orbital angular momentum in gauge theories: Nucleon spin structure and multipole radiation revisited" [PRL 100:232002 (2008)]
• Spin and orbital angular momentum in gauge theories: Nucleon spin structure and multipole radiation revisited
• Single Transverse Spin Asymmetry for Large-p_T Pion Production in Semi-Inclusive Deep Inelastic Scattering
• Do gluons carry half of the nucleon momentum?
• Low-momentum interactions with smooth cutoffs
• Gauge- and frame-independent decomposition of nucleon spin
• Nucleon spin decomposition and differential geometry
• Angular momentum decomposition from a QED example
• Boundary terms in quantum field theory and the spin structure of QCD

Cited by in corpus (3)

• Unravelling the physical meaning of the Jaffe-Manohar decomposition of the nucleon spin
• Revisiting the compatibility problem between the gauge principle and the observability of the canonical orbital angular momentum in the Landau problem
• On the decomposition theorem for gluons