Non-conformal renormalised stress tensors in Robertson-Walker space-times

A number of explicitly soluble models of a massless, non-conformally-coupled scalar quantum field propagating in certain special Robertson-Walker background space-times are considered. Regularisation is effected using covariant point-splitting, and renormalised stress tensors are constructed according to the ansatz, described elsewhere (Bunch and Davies Proc. R. Soc.; A360:117 (1978)), based on the DeWitt-Schwinger expansion. The results are all finite, conserved and free of regularisation ambiguities. From these special cases it is possible to deduce a great deal about the structure of renormalised stress tensors in more general models in which computation-approximation techniques will be necessary. (author)