ISOTROPIZATION OF BIANCHI-TYPE COSMOLOGICAL SOLUTIONS IN BRANS-DICKE THEORY

The cosmic, general analytic solutions of the Brans-Dicke theory for the hat Friedmann-Robertson-Walker (FRW) models containing perfect, barotropic, fluids are seen to belong to a wider class of solutions, which includes cosmological models with the open and the closed spaces of the FRW metric, as well as solutions for models with homogeneous but anisotropic spaces corresponding to the Bianchi-type metric classification, when all these solutions are expressed in terms of reduced variables. The existence of such a class lies in the fact that the scaled scalar-field psi = phi alpha(3(1-beta)) (with alpha(3) alpha(1) alpha(2) alpha(3) the ''volume element'' and beta the barotropic index, p = beta rho) can be written as a quadratic function of the scaled time and this solution is independent of the metrics here employed. This reduction procedure permits one to analyze if explicitly given anisotropic cosmological solutions ''isotropize'' in, the course of their time evolution. If this can happen, it could be claimed that there exists a subclass of solutions that is stable under anisotropic perturbations: This seems to be the case for the Bianchi type I, V, and IX.