2023/08/26 by Qi Dai, Ziwei Chen, Dai, Qi +5
Engineering · Physics and Astronomy · #Geophysics and Sensor Technology #Mechanical and Optical Resonators #Quantum and Classical Electrodynamics
paper · pdf · doi:10.48550/arxiv.2309.07130
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 ∫ d3 x\boldsymbolE and angular momentum ∫ d3 x (\boldsymbolr×\boldsymbolE) for a free electromagnetic wave, which are conserved quantities during propagation in vacuum.