Generating lambda from the vacuum

Abstract

The close relationship between the cosmological constant and the vacuum has been emphasised in the past by Zeldovich amongst others. We briefly discuss different approaches to the cosmological constant issue including the possibility that A could be generated by vacuum polarization in a static Universe. Fresh possibilities occur in an expanding Universe. An Inflationary Universe generically leads to particle creation from the vacuum, the nature and extent of particle production depending upon the mass of the field and ~ts coupling to gravity. For ultra-light, non-minimally coupled scalar fields, particle production can be large and the resulting vacuum energy-momentum tensor will have the form of an effective cosmological constant. The Inflationary scenario therefore, could give rise to a Universe that is both flat and A-dominated, in agreement with observations.