RESUMEN

Alpha vacua in de Sitter space have the potential to make interesting modifications to the predictions of inflation, and provide new mechanisms for the generation of ultra high-energy cosmic rays. Currently there are several different approaches to defining alpha-vacua at the interacting level. We describe how these approaches are related, and elaborate on one approach which leads to a consistent renormalizable perturbative expansion around a fixed de Sitter background. Nevertheless, we argue even this approach fails when coupling to gravity is taken into account, for all but the Bunch-Davies vacuum. Possible ways to avoid this no go theorem are discussed.