Quantum field theory in curved space-time. Massive and massless vector fields

In this paper we present a quantum field formulation for massive and massless vector fields in curved space-time. This is carried out by using the general theory of Green's functions. Further on, we apply our general formalism to the Robertson-Walker spatially flat model of an expanding Universe. This allows us to show that in a metric which has some symmetry properties it is possible to define conserved dynamical quantities, analogous to those of flat space-time