Singularities and isotropy in a Brans-Dicke Bianchi-type VII universe

TL;DR

This paper investigates the early universe's anisotropic expansion in Brans-Dicke scalar-tensor cosmology, revealing conditions under which models become isotropic or develop strong curvature singularities, affecting the universe's initial and final states.

Contribution

It provides analytical solutions for Bianchi type VII models in Brans-Dicke theory, showing isotropic expansion in one case and singularities in others, advancing understanding of initial singularities in scalar-tensor cosmology.

Findings

Bianchi-VII$_0$ model exhibits isotropic expansion akin to FRW universe.

Bianchi-VII$_h$ models with $h eq 0$ develop strong curvature singularities.

The universe's evolution can begin and end in singularities or collapse to lower-dimensional structures.

Abstract

We study the dynamical effects in the scale factors due to the scalar $\phi$-field at the early stages of a supposedly anisotropic Universe expansion in connection with the problem of the initial singularity in the scalar-tensor cosmology of Jordan-Brans-Dicke. This is done by considering the behaviour of the general analytical solutions for the homogeneous model of Bianchi type VII in the vacuum case. We conclude that the Bianchi-VII$_0$ model shows an isotropic expansion and that its only physical solution is equivalent to a Friedman-Robertson-Walker spacetime whose evolution begins in a singularity and ends in another; moreover, we obtain that the general Bianchi-VII$_h$ (with $h\neq 0$) models show strong curvature singularities that produces a complete collapse of the homogeinity surfaces to a 2-plane, to a string-like one-dimensional manifold, or to a single point.