[en] It is shown that the (quantum or classical) observables for a spin-1/2 massive electron are invariant under a local one-parameter group of gauge transformations whose generator is dependent on the fermion 'fields' of the theory, as well as conventional (constant) Lie algebra generators. This one-parameter family of local transformations is 2 → 1 homomorphic to a set of operators common to both the 'little group' of the four-velocity and the 'little group' of the Pauli-Lubanski spin vector. This symmetry is called the 'local little symmetry' to emphasize its connection to Wigner's 'little group'. The physical origin of this local little symmetry' is discussed. This symmetry is employed to explain a degeneracy exhibited by some classical models of an electron with spin

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[en] In this paper, we have proposed an improved convolutional neural network model based on the ShuffleNet V2 network for recognizing the orbital angular momentum (OAM) modes for the OAM based free space optical communication systems in the environments of atmospheric turbulence (AT). The network is trained by inputting the intensity images of the Laguerre Gaussian beams, which can effectively finish the training process due to its special designs, and can recognize the OAM modes with high accuracy. Compared with previous works for the single and multiplexing OAM modes, the proposed network model has high-precision and high-efficiency characteristics. Especially for the multiplexing OAM modes, our proposed system can achieve the recognition accuracy of 99.5% under strong AT and long-distance transmission. In addition, in order to prove that our system has good generalization ability and strong robustness, we used the trained model to test several groups of data obtained under untrained AT intensities, and the results showed that our model could still maintain high accuracy under the untrained AT intensities, which is very important to the realization of high-capacity optical communication technologies based on OAM in the future (paper)

[en] We consider the behaviour of the orbital angular momentum of the light field as a superposition of Hermite – Gaussian beams upon astigmatic mode conversion. An analytical expression is obtained for the orbital angular momentum of such fields. Expressions are found for various linear combinations of Hermite – Gaussian beams. The astigmatic mode conversion of the initial light fields that are equivalent from the point of view of the orbital angular momentum is shown to lead to significantly different final results. (paper)

[en] Transverse-momentum-dependent parton distributions (TMDs) are crucial ingredients for a complete understanding of the dynamics of confined par-tons. They allow for a 3-dimensional description of the nucleon in momentum space, and could provide insights into the yet unmeasured quark orbital angular momentum. At CLAS several TMDs are explored in Fourier analysis of azimuthal asymmetries measured in semi-inclusive DIS. An overview of the main CLAS results as well as selected CLAS12 projected results is presented.

[en] Recent studies have attributed certain properties of the Earth's atmosphere to excess orbital angular momentum of impinging meteoroids. A realistic analysis of meteor observations does not support the existence of this excess. (Auth.)

[en] The Wigner function of a pure continuous-variable quantum state is non-negative if and only if the state is Gaussian. Here we show that for the canonical pair angle and angular momentum, the only pure states with non-negative Wigner functions are the eigenstates of the angular momentum. Some implications of this surprising result are discussed.

[en] Multistaircase spiral phase plates (MSSPPs), which are alternatives to ideal continuous surface SPPs, are commonly applied to passively generate optical vortices (OVs). In addition, one of the universal applications of OVs is in orbital angular momentum (OAM)-multiplexed quadrature amplitude modulation (QAM) optical communication systems. In this paper, the relationship between bit error rate (BER) performance and the key parameters of the MSSPPs, e.g. the number of staircases M and the topological charge l, is researched, and four OAM-multiplexed QAM systems with different modulation orders (16 QAM, 32 QAM, 64 QAM and 256 QAM) are qualitatively and quantitatively evaluated. Theoretical analysis and the simulation results show that OAM multiplexing leads to negative impacts on BER performance. The impacts include a decrease in the power of the useful signal and possible crosstalk between OAM-multiplexed paths. In addition, appropriately setting M, l and the modulation order can help reduce the impact of the power decrease and avoid crosstalk. This work provides a reference for practical OAM-multiplexed QAM systems based on MSSPPs. (letter)

[en] Possibility of applicability of quasi-classical description of particle motion with spin 1/2 in periodical external field is discussed. An equation of Bargman-Michel-Telegdi (BMT) in operator form is derived. The operators are taken in the representation generalized for the case of external fields, where operator of polarization in the first order over the charge is the Pauli matrix. It is shown that the classical equation BMT can be correctly applied only together with the equation for trajectory of particle without spin. 9 refs

No abstract available