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arXiv 0802.4453gr-qcmath-phmath.MP
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经典电磁学的几何表述

Geometrical formulation of classical electromagnetism

Nikodem J. Poplawski

摘要:

一般的仿射联络有足够的自由度来描述引力的度量仿射公式中的经典引力场和电磁场。引力场在拉格朗日量中由里奇张量的对称部分表示,而经典电磁场则由位似曲率张量几何表示。我们引入的四速度场的运动学约束,其中的拉格朗日乘子代表的能量密度的问题。四速度和非度规张量的迹之间的耦合表示电荷密度。我们表明,最简单的度量仿射拉格朗日依赖于Ricci张量和位似曲率张量产生的爱因斯坦-麦克斯韦场方程,而Bianchi恒等式给出洛伦兹运动方程。如果四速度耦合到挠率矢量,爱因斯坦方程就被一个在普朗克尺度下很重要的项所修正,这可能会阻止时空奇点的形成。

英文摘要:

A general affine connection has enough degrees of freedom to describe the classical gravitational and electromagnetic fields in the metric-affine formulation of gravity. The gravitational field is represented in the Lagrangian by the symmetric part of the Ricci tensor, while the classical electromagnetic field is represented geometrically by the tensor of homothetic curvature. We introduce matter as the four-velocity field subject to the kinematical constraint in which the Lagrange multiplier represents the energy density. A coupling between the four-velocity and the trace of the nonmetricity tensor represents the electric charge density. We show that the simplest metric-affine Lagrangian that depends on the Ricci tensor and the tensor of homothetic curvature generates the Einstein-Maxwell field equations, while the Bianchi identity gives the Lorentz equation of motion. If the four-velocity couples to the torsion vector, the Einstein equations are modified by a term that is significant at the Planck scale and may prevent the formation of spacetime singularities.

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