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The partition of nucleon spin between total angular momenta of quarks and gluons is described by the energy momentum tensor formfactors manifested also in the nucleon scattering by weak classical gravitational field. Natural generalization…
Spin angular momentum of a photon corresponds to a polarisation degree of freedom of lights, and such that various polarisation properties are coming from macroscopic manifestation of quantum-mechanical properties of lights. An orbital…
This paper analyzes the algebraic and physical properties of the spin and orbital angular momenta of light in the quantum mechanical framework. The consequences of the fact that these are not angular momenta in the quantum mechanical sense…
Whether the total angular momentum of the photon can be separated into spin and orbital parts has been a long-standing problem due to the constraint of transversality condition on its vector wavefunction. A careful analysis shows that the…
It is unavoidable to deal with the quark and gluon momentum and angular momentum contributions to the nucleon momentum and spin in the study of nucleon internal structure. However, we never have the quark and gluon momentum, orbital angular…
Recently, the problem of spin and orbital angular momentum (AM) separation has widely been discussed. Nowadays, all discussions about the possibility to separate the spin AM from the orbital AM in the gauge invariant manner are based on the…
Light beams carrying orbital angular momentum, such as Laguerre-Gaussian beams, give rise to the violation of the standard dipolar selection rules during the interaction with matter yielding, in general, an exchange of angular momentum…
A classical circularly polarized electromagnetic wave carries angular momentum, and represents the classical limit of a photon, which carries quantized spin. It is shown that a very similar picture of a circularly polarized coherent wave…
We demonstrate that there exist two kinds of gauge-invariant decompositions of the nucleon spin, which are physically inequivalent. The quark and gluon orbital angular momenta (OAMs) appearing in one decomposition are basically the…
In condensed matter systems it is necessary to distinguish between the momentum of the constituents of the system and the pseudomomentum of quasiparticles. The same distinction is also valid for angular momentum and pseudoangular momentum.…
A system consisting of a point material particle and a scalar field described by the nonlinear Klein-Gordon equation has been considered. It has been shown that, when taking into account relativistic effects, in the case of small rest…
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…
It is shown that the photon picture of the electromagnetic field enables one to determine unambiguously the splitting of the total angular momentum of the electromagnetic field into the orbital part and the spin part.
One intriguing issue in the nucleon spin decomposition problem is the existence of two types of decompositions, which are representably characterized by two different orbital angular momenta (OAMs) of quarks. The one is the manifestly…
Based on gauge-invariant decomposition of covariant angular momentum tensor of QCD in an arbitrary Lorentz frame, we investigate the relation between the known decompositions of the nucleon spin into its constituents, thereby clarifying in…
We review studies of the fluctuations of light made accessible by the invention of the laser and the strong interactions realized in cavity QED experiments. Photon antibunching advocating the discrete (particles), is contrasted with…
Recent experiment demonstrates magnon to phonon conversion in a YIG film under the application of a non-uniform magnetic field. Light scattered from phonons is observed to change its polarization state interpreted by the authors signifying…
The twenty years since the announcement of the proton spin crisis by the European Muon Collaboration has seen tremendous progress in our knowledge of the distribution of spin within the proton. The problem is reviewed, beginning with the…
The authors claim to have found a "proper", "gauge-invariant" definition of a charged-particle's momentum in gauge theory, which is more "superior" than the textbook version. I show that their result arises from a misunderstanding of gauge…
We address the problem of angular momentum decomposition of a free photon. We propose a natural and physical scheme for separating the total angular momentum operator for a free photon into an orbital part and a spin part with the hope that…