Verification of unitary equivalence of gauges in QED

In our previous paper we verified unitary equivalence between the axial and Coulomb gauge formulations in QED. To this end we restored gauge freedom by introducing a pair of conjugate zero norm fields. In this paper we extend the method to other linear gauges with time derivative of A0. It is shown that introducing another auxiliary field together with the zero norm fields enables us to construct a consistent canonical formulation in an extended indefinite metric Hilbert space. It is also shown that in this formulation we get freedom of residual gauge transformations Aμ → Aμ + ∂μΛ with Λ satisfying □2Λ = 0 so that we can verify gauge equivalence in the same manner among a class of gauges specified by one-gauge parameter such as ∂μAμ + αB = 0. (author)