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arXiv 1208.4523physics.opticshep-thquant-ph
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对偶电磁学:螺旋度、自旋、动量和angular momentum

Dual electromagnetism: Helicity, spin, momentum, and angular momentum

Konstantin Y. Bliokh, Aleksandr Y. Bekshaev, Franco Nori

摘要:

电场和磁场的对偶对称性是自由空间中麦克斯韦方程组的一个重要的本征性质。这种对称性是光学螺旋度守恒的基础,正如我们在这里所展示的,它与光的自旋和轨道自由度的分离密切相关(螺旋度通量与自旋角动量一致)。然而,在电磁学的标准场论公式中,场拉格朗日量不是对偶对称的。这导致了正则能量-动量、自旋和轨道角动量张量的双重不对称形式。此外,我们表明,这些张量的组件与螺旋度和能量守恒定律的冲突。为了解决拉格朗日方程组和麦克斯韦方程组对称性之间的矛盾,我们提出了经典电磁学的双对称拉格朗日方程组。这种对偶电磁学保持了麦克斯韦方程组的形式,产生了有意义的正则能量-动量和角动量张量,并确保了自旋和轨道自由度的自洽分离。这提供了在其他最近的方法中建议的结果的严格推导。我们对对偶对称性和所有的庞加莱对称性进行了诺特分析,考察了局部和积分守恒量,并表明只有对偶电磁学才能自然地产生一套完整的自洽守恒律。我们还讨论了区分标准和对偶理论的物理量的可观测性,以及与量子弱测量和各种光学实验的关系。

英文摘要:

The dual symmetry between electric and magnetic fields is an important intrinsic property of Maxwell equations in free space. This symmetry underlies the conservation of optical helicity, and, as we show here, is closely related to the separation of spin and orbital degrees of freedom of light (the helicity flux coincides with the spin angular momentum). However, in the standard field-theory formulation of electromagnetism, the field Lagrangian is not dual symmetric. This leads to problematic dual-asymmetric forms of the canonical energy-momentum, spin, and orbital angular momentum tensors. Moreover, we show that the components of these tensors conflict with the helicity and energy conservation laws. To resolve this discrepancy between the symmetries of the Lagrangian and Maxwell equations, we put forward a dual-symmetric Lagrangian formulation of classical electromagnetism. This dual electromagnetism preserves the form of Maxwell equations, yields meaningful canonical energy-momentum and angular momentum tensors, and ensures a self-consistent separation of the spin and orbital degrees of freedom. This provides rigorous derivation of results suggested in other recent approaches. We make the Noether analysis of the dual symmetry and all the Poincaré symmetries, examine both local and integral conserved quantities, and show that only the dual electromagnetism naturally produces a complete self-consistent set of conservation laws. We also discuss the observability of physical quantities distinguishing the standard and dual theories, as well as relations to quantum weak measurements and various optical experiments.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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