Inhomogeneous Gravity

TL;DR

This paper investigates how the gravitational constant G varies in different regions of the universe within scalar-tensor theories, using exact solutions and matching techniques to compare local and cosmological evolution.

Contribution

It introduces a method to model the evolution of G in inhomogeneous cosmologies and compares local and global variations within scalar-tensor frameworks.

Findings

Slower evolution of ot;G in virialized clusters compared to the background universe.

Developed a matching technique for different scalar-tensor cosmologies.

Applied the model to a DM universe with spherical inhomogeneities.

Abstract

We study the inhomogeneous cosmological evolution of the Newtonian gravitational 'constant' G in the framework of scalar-tensor theories. We investigate the differences that arise between the evolution of G in the background universes and in local inhomogeneities that have separated out from the global expansion. Exact inhomogeneous solutions are found which describe the effects of masses embedded in an expanding FRW Brans-Dicke universe. These are used to discuss possible spatial variations of G in different regions. We develop the technique of matching different scalar-tensor cosmologies of different spatial curvature at a boundary. This provides a model for the linear and non-linear evolution of spherical overdensities and inhomogeneities in G. This allows us to compare the evolution of G and \dot{G} that occurs inside a collapsing overdense cluster with that in the background universe. We develop a simple virialisation criterion and apply the method to a realistic lambda-CDM cosmology containing spherical overdensities. Typically, far slower evolution of \dot{G} will be found in the bound virialised cluster than in the cosmological background. We consider the behaviour that occurs in Brans-Dicke theory and in some other representative scalar-tensor theories.