For 10 points, identify this operation which modifies some field configuration while leaving observables unchanged.
The Power-Zeinau-Woolley operation is an example of this type of operation. In Dirac's derivation of magnetic monopoles as strings of dipoles, this operation is equivalent to moving between two strings. In Yang-Mills theory, this operation corresponds to a changing of the color orientation of the matter field. In QED, this operation is realized on the Dirac field as a local phase rotation, under which the QED Lagrangian is invariant. That invariance under this operation implies the conservation of charge by Noether's theorem, and in classical electrodynamics this operation equates to adding the gradient of an arbitrary function to the vector potential. For 10 points, identify this operation which modifies some field configuration while leaving observables unchanged.
The Power-Zeinau-Woolley operation is an example of this type of operation.
gauge transformation