de Sitter vacua, renormalization, and locality

We analyze the renormalization properties of quantum field theories in de Sitter space and show that at most two of the maximally invariant vacuum states of free fields lead to consistent perturbation expansions. One is the Euclidean vacuum. The other is consistent with an interpretation as an antipodal orbifold of de Sitter space. We provide a Hamiltonian quantization in which this vacuum is viewed as living on the future half of global de Sitter space with boundary conditions on fields at the origin of time. We argue that the perturbation series in this case has divergences at the origin which render the future evolution of the system indeterminate, without a better understanding of high energy physics.