Noise induced transitions in semiclassical cosmology - art. no. 083513

A semiclassical cosmological model is considered which consists of a closed Friedmann-Robertson-Walker spacetime in the presence of a cosmological con stant, which mimics the effect of an inflaton held, and a massless, non-con formally coupled quantum scalar held. We show that the hack-reaction of the quantum field. which consists basically of a nonlocal term due to gravitat ional particle creation and a noise term induced by the quantum fluctuation s of the field, are able to drive the cosmological scale factor over the ba rrier of the classical potential so that if the universe starts near a zero scale factor (initial singularity), it can make the transition to an expon entially expanding de Sitter phase. We compute the probability of this tran sition and it turns out to be comparable with the probability that the univ erse tunnels from "nothing" into an inflationary stage in quantum cosmology . This suggests that in the presence of matter fields the hack-reaction on the spacetime should not be neglected in quantum cosmology. [S0556-2821(99) 04108-9].