On the problem of the initial state in the isotropic scalar-tensor cosmology of Brans-Dicke

Abstract

In connection with the problem of the initial singularity in the framework of the Brans-Dicke scalar-tensor isotropic cosmology, the dynamics of the early stages of the expansion is studied on the basis of the general analytical solutions for flat models withP=ne (0≤n≤1). The sourceless scalar field, which plays a role of effective source of the geometry, entirely changes the character of the initial expansion, whereas in the absense of it the dynamics of the models almost does not differ from GR-case. If the connecting parameter ω 1/3e parallel with the vacuum singularity the singular initial state with dominant role of gravitating matter is possible. In the course of expansion, the influence of gravitating matter and curvature-which as nonessential at the early stage in comparison with sourceless ϕ-field — becomes dominant, and all models approach the ‘Machian’ ones which differs slightly from corresponding GR-models. If ω is negative (ω<−6) the sourceless ϕ-field slows down the initial expansion and increases essentially the real age of the Universe; it can also influence the primordial nuclear synthesis by diminishing in particular the content of He4. It is shown that a knowledge of the signĠ gives us the information about the nature of the initial Universe state.