Is there a link between gauge invariance, relativistic invariance and electron spin?

Abstract

Without any assumptions other than the theory of classical electrodynamics applied to the problem of a charged particle interacting with the field of an electromagnetic plane wave, an operator is derived which has no other significance than the motion of the spin of a Dirac particle, given by the solution of the Bargmann-Michel-Telegdi equation. It is shown that the motion of an electron and the motion of its spin in a plane wave are given by an operator of Lorentz type which has the remarkable property of being equivalent to a gauge transformation.