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arXiv · 2309.07130

More on difference between angular momentum and pseudo-angular momentum

Qi Dai·Zi-Wei Chen·Bang-Hui Hua·Xiang-Song Chen
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Abstract

We extend the discussion on the difference between angular momentum and pseudo-angular momentum in field theory. We show that the often quoted expressions in [Phys.Rev.B 103, L100409 (2021)] only apply to a non-linear system, and derive the correct rotation symmetry and the corresponding angular momentum for a linear elastic system governed by Navier-Cauchy equation. By mapping the concepts and methods for the elastic wave into electromagnetic theory, we argue that the renowned canonical and Benlinfante angular momentum of light are actually pseudo-angular momentum. Then, we derive the ``Newtonian" momentum $\int \text{d}^3 x\boldsymbol{E}$ and angular momentum $\int \text{d}^3 x (\boldsymbol{r}\times\boldsymbol{E})$ for a free electromagnetic wave, which are conserved quantities during propagation in vacuum.

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Qi Dai, Zi-Wei Chen, Bang-Hui Hua, Xiang-Song Chen. 2023-08-26. More on difference between angular momentum and pseudo-angular momentum. https://arxiv.org/abs/2309.07130

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