A note on α-vacua and interacting field theory in de Sitter space

Using an imaginary time formalism, we propose a consistent renormalizable perturbation theory of a scalar field in a non-trivial a vacuum in de Sitter space. Although one representation of the effective action involves non-local interactions between anti-podal points, we argue the theory leads to causal physics when continued to real-time, and we prove a spectral theorem for the interacting two-point function. We construct the renormalized stress energy tensor and show this develops no imaginary part at leading order in the interactions, consistent with stability. (C) 2003 Elsevier B.V. All rights reserved.