Quantum instability of de Sitter spacetime

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Abstract
Various interacting field theories in de Sitter spacetime which contain a massless, minimally coupled scalar field are investigated. It is shown that the vacuum expectation value of the energy-momentum tensor can contain a term which is proportional to the metric tensor but with a coefficient which, to first order in the coupling constant, is a linear function of time. This term can act in such a way as to tend to cancel the cosmological constant and to cause the curvature of de Sitter space to decrease. The possibility that pure quantum gravity without matter fields may lead to an instability of de Sitter space is also discussed.