Semiclassical cosmology with a scalar field

Abstract

A self consistent scheme for studying the semiclassical limit of a quantized scalar field in a classical Robertson-Walker metric is developed. The scalar field is chosen to be in a Gaussian state. The classical and semiclassical geometries are contrasted; and it is shown that nontrivial solutions exist for the space-time geometry which are driven by the vacuum fluctuations of the scalar field. We also discuss the stability of de Sitter space to quantum fluctuations, if the cosmological constant is larger than a critical value.