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Differences between vector potentials in different gauges contain no dynamicsin both classical and quantum electrodynamics and chromodynamics. Consequently,once gauge invariance is established, results calculated in non-covariantgauges can be expected to agree with results obtained in covariant gauges inall Lorentz frames. We show in particular that canonical quantization in theCoulomb gauge can be used without giving up explicit gauge invariance.Quantization in the Coulomb gauge is particularly simple because it involvesonly the two transverse photons/gluons present in all gauges. These transversephotons/gluons reside on a 2-dimensional physical plane in momentum spaceperpendicular to the photon/gluon momentum {\bf k}. Explicit expressions aregiven for the basic momentum, spin and orbital angular momentum field operatorsof photons/gluons in the Coulomb gauge. Their properties are discussed in somedetail. In particular, these field operators are shown to be more complicatedthan the corresponding operators in quantum mechanics which they also contain.

Gauge-invariant momentum and angular momentum operators in quantum electrodynamics and chromodynamics