Related papers: The angular momentum controversy: What's it all ab…
The past decades have seen substantial interest in the so-called orbital angular momentum (OAM) of light, driven largely by its diverse range of applications. However, there are fundamental theoretical issues with decomposing the angular…
Differences between vector potentials in different gauges contain no dynamics in both classical and quantum electrodynamics and chromodynamics. Consequently, once gauge invariance is established, results calculated in non-covariant gauges…
The exact decomposition of the proton spin has been a much debated topic, on the experimental as well as the theoretical side. In this talk we would like to report on recent non-perturbative results and ongoing efforts to explore the proton…
The anomalous dimension for the gauge-invariant-canonical decomposition of the energy-momentum tensor for quarks and gluons is studied by the background field method. In particular, the consistency between the background field method and…
We compare three attempts that have been made to decompose the angular momentum of the electromagnetic field into components of an "orbital" and "spin" nature. All three expressions are different and it appears, on the basis of classical…
In the past few years, a lot of evidences have been accumulated, which indicate that the gluon polarization inside the nucleon is likely to be small at least at the low renormalization scales. On the other hand, the recent lattice QCD…
In recent papers, we have established the existence of gauge-invariant decomposition of nucleon spin, each term of which can be related to known high-energy deep-inelastic-scattering observables. A subtlety remains, however, for the…
We investigate the different decompositions of the angular momentum in QCD for a relativistic spin $1/2$ composite state, namely a quark dressed with a gluon. We use light-front Hamiltonian perturbation theory, and in the light-front gauge,…
The fundamental program in high energy spin physics focuses on the spin structure of the nucleon. The gluon and orbital angular momentum components of the nucleon spin are virtually unknown. The J_z=1/2 sum rule involves the integrated…
This talk consists of four parts. In part one, I give an elementary discussion on constructing a Lorentz-invariant spin sum rule for the nucleon. In part two, I discuss a gauge-dependent spin sum rule, explore its relation with the…
We study the chromodynamical gauge symmetry in relation to the internal spin structure of the nucleon. We show that 1) even in the helicity eigenstates the gauge-dependent spin and orbital angular momentum operators do not have…
We discuss the different types of decomposition of the proton spin. We stress that, despite their lack of uniqueness, the Chen et al. and Wakamatsu decompositions are perfectly measurable. We argue that a large part of the recent…
What are gravitational waves? How do they propagate? and what is their energy content? These questions are addressed in the first two chapters. In the third chapter the pseudo-Newtonian formalism and its extension is reviewed in general and…
By separating the gluon field into physical and pure-gauge components, the usual Poincar\'e subalgebra for an interacting system can be reconciled with gauge-invariance when decomposing the total rotation and translation generators of QCD…
It is argued by the author that the canonical form of the quark energy-momentum tensor with a partial derivative instead of the covariant derivative is the correct definition for the quark momentum and angular momentum fraction of the…
We present a scheme well-suited to investigate quantitatively the angular momentum coherence of molecular fragments. Assuming that the dissociated molecule has a null total angular momentum, we investigate the propagation of the…
A controversy is raging concerning the most physically meaningful definition of quark and gluon angular momentum, a question of importance in understanding the internal structure of the nucleon. There are, in my, opinion, two principal…
The spin structure of nucleon at twist 2 and 3 levels is analyzed. The contribution of quark and gluon spins to nucleon spin are Lorentz invariant, while it is not sure for orbital angular momentum. The conserved fractional moments of…
Gauge invariance, a core principle in electrodynamics, has two separate meanings. One concept treats the photon as the gauge particle for electrodynamics. It is based on symmetries of the Lagrangian, and requires no mention of electric or…
A new debate has recently arisen on the subject of orbital angular momentum in QCD, in particular on its observability and on its partonic interpretation. Orbital momentum can be defined in QCD using two different decomposition schemes that…