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arXiv 2103.14241physics.class-ph
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高阶电磁场论中能量动量张量的规范对称化方法

A gauge-symmetrization method for energy-momentum tensors in high-order electromagnetic field theories

Peifeng Fan, Jianyuan Xiao, Hong Qin

摘要:

对于电磁场论,正则的能量-动量守恒定律可以根据Noether过程从支撑时空平移对称性导出。然而,正则能量动量张量(EMT)既不是对称的,也不是规范对称的(规范不变量)。Belinfante-Rosenfeld(BR)方法是一种众所周知的对称化EMT的方法,这也使它们成为一阶场论的规范对称。高阶电磁场论出现在磁化等离子体的回旋动力学系统和经典带电粒子辐射反应的波多尔斯基系统的研究中。对于这些高阶场论,规范对称的EMT不一定是对称的,反之亦然。在本研究中,我们发展了高阶电磁场论中EMT的规范对称化方法。用Faraday张量F代替四维势A,用Noether方法导出了正则EMT T_N。我们证明了T_N的规范依赖部分可以用位移-势张量\mathcal{F} = \mathcal{D} *A/4π去除,其中\mathcal{D}是反对称电位移张量.这种方法使EMT规范对称化,而不必使其对称,这对于不涉及广义相对论的应用是足够的。对于一阶电磁场论,如标准Maxwell系统,\mathcal{F}简化为熟悉的BR超势\mathcal{S},并且所发展的方法可以用作计算\mathcal{S}的更简单的过程,而不需要使用4D时空中的角动量张量。当电磁系统与经典带电粒子耦合时,规范对称化方法也是有效的。

英文摘要:

For electromagnetic field theories, canonical energy-momentum conservation laws can be derived from the underpinning spacetime translation symmetry according to the Noether procedure. However, the canonical Energy-Momentum Tensors (EMTs) are neither symmetric nor gauge-symmetric (gauge invariant). The Belinfante-Rosenfeld (BR) method is a well-known procedure to symmetrize the EMTs, which also renders them gauge symmetric for first-order field theories. High-order electromagnetic field theories appear in the study of gyrokinetic systems for magnetized plasmas and the Podolsky system for the radiation reaction of classical charged particles. For these high-order field theories, gauge-symmetric EMTs are not necessarily symmetric and vice versa. In the present study, we develop a new gauge-symmetrization method for EMTs in high-order electromagnetic field theories. The Noether procedure is carried out using the Faraday tensor F, instead of the 4-potential A, to derive a canonical EMT T_N. We show that the gauge-dependent part of T_N can be removed using the displacement-potential tensor \mathcal{F}=\mathcal{D}*A/4π, where \mathcal{D} is the anti-symmetric electric displacement tensor. This method gauge-symmetrize the EMT without necessarily making it symmetric, which is adequate for applications not involving general relativity. For first-order electromagnetic field theories, such as the standard Maxwell system, \mathcal{F} reduces to the familiar BR super-potential \mathcal{S}, and the method developed can be used as a simpler procedure to calculate \mathcal{S} without employing the angular momentum tensor in 4D spacetime. When the electromagnetic system is coupled to classical charged particles, the gauge-symmetrization method for EMTs is shown to be effective as well.

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