Energy-momentum tensor renormalization for vector fields in Robertson-Walker backgrounds

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Abstract
In this paper we generalize the Stueckelberg formalism of flat spacetime to describe vector fields propagating in a Robertson-Walker spatially flat background. In the zero-mass limit of the regularized energy-momentum tensor we recover the usual vacuum-polarization terms of the massless Maxwell theory. Further on we investigate particle creation and the renormalizability of the energy-momentum tensor expectation value in the vacuum state which minimizes the metric Hamiltonian. In the massive case we found that the last one corresponds to that obtained through the Higgs mechanism and that it is not renormalizable in general. In the massless case we found that both quantities are finite and are in agreement with those in the literature obtained by different regularization methods, the resulting vacuum being the standard conformal one.