Isotropisation of Generalized Scalar-Tensor theory plus a massive scalar field in the Bianchi type I model

TL;DR

This paper investigates how a generalized scalar-tensor theory with a massive scalar field evolves towards isotropy in a Bianchi type I cosmological model, revealing conditions on the coupling and potential that lead to power or exponential expansion.

Contribution

It generalizes previous results by unifying isotropisation conditions for scalar-tensor theories with different potentials and coupling functions in Bianchi type I models.

Findings

Metric functions tend toward power or exponential laws asymptotically.

Isotropisation depends on conditions on the Brans-Dicke coupling and potential.

Results extend previous models with cosmological constant and exponential potential.

Abstract

In this paper we study the isotropisation of a Generalized Scalar-Tensor theory with a massive scalar field. We find it depends on a condition on the Brans-Dicke coupling function and the potential and show that asymptotically the metric functions always tend toward a power or exponential law of the proper time. These results generalise and unify these of De Sitter in the case of a cosmological constant and of Cooley and Kitada in the case of an exponential potential.