Lorenz gauge and the Poisson bracket in canonical electromagnetism

Abstract: In treatments of electromagnetism, it is often tacitly assumed that the vector potentials of the field and their conjugate momenta satisfy the canonical Poisson bracket relations, despite the fact that the components of the vector potential are constrained by gauge conditions. Here I explicate how this comes about by imposing Poisson bracket relations on the independent field variables remaining after the Lorenz gauge constraint is accounted for. The naively assumed Poisson brackets happens to be correct even after gauge fixing, owing to a conspiracy between the gauge conditions and the principle of relativity.