The construction of physical states for a scalar quantum field in a Bianchi type-I universe is analyzed. A local constraint based upon the Hadamard form of the anticommutator function is implemented. The constraints imposed on the Fock space by this requirement are derived and the unitary equivalence between different representations of canonical commutation relations is shown. Within this formalism we analyze recently proposed Fock-space constructions and we show the uniqueness of the inflationary vacuum.

• Received 18 October 1985

DOI:https://doi.org/10.1103/PhysRevD.33.3581