关于量子电动力学中极化矢量的一点注记
A Note on Polarization Vectors in Quantum Electrodynamics
摘要：
一个动量为k的光子只能有两个偏振态，而不是三个。同样地，我们可以说磁矢势A在库仑规范中一定是无发散的。在QED中通常通过引入两个偏振矢量λ_λ（k）来考虑这些事实，其中λ在{1，2}中，它们与波矢量k正交。这些向量必须是k的非常不连续的函数，因此，它们的傅里叶变换具有不良的衰减特性。由于这些矢量没有物理意义，因此必须有一种方法从理论中消除它们及其不良的衰变性质。我们在这里提出这样一种方式。
英文摘要：
A photon of momentum k can have only two polarization states, not three. Equivalently, one can say that the magnetic vector potential A must be divergence free in the Coulomb gauge. These facts are normally taken into account in QED by introducing two polarization vectors epsilon_λ(k) with lambda in {1,2}, which are orthogonal to the wave-vector k. These vectors must be very discontinuous functions of k and, consequently, their Fourier transforms have bad decay properties. Since these vectors have no physical significance there must be a way to eliminate them and their bad decay properties from the theory. We propose such a way here.
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