Cosmological Constant in Chameleon Brans-Dicke Theory

TL;DR

This paper explores a generalized Brans-Dicke model with a self-interacting scalar field that exhibits chameleon behavior, analyzing exact solutions for different matter couplings and their effects on vacuum density during cosmic expansion.

Contribution

It introduces a generalized Brans-Dicke framework with a density-dependent scalar field, providing exact solutions for dust and vacuum matter couplings with implications for cosmological evolution.

Findings

Exact exponential solutions for dust matter coupling.

Power-law solutions showing vacuum density decay.

Chameleon behavior influences cosmic expansion dynamics.

Abstract

We consider a generalized Brans-Dicke model in which the scalar field has a self-interacting potential function. The scalar field is also allowed to couple non-minimally with the matter part. We assume that it has a chameleon behavior in the sense that it acquires a density-dependent effective mass. We consider two different types of matter systems which couple with the chameleon, dust and vacuum. In the first case, we find a set of exact solutions when the potential has an exponential form. In the second case, we find a power-law exact solution for the scale factor. In this case, we will show that the vacuum density decays during expansion due to coupling with the chameleon.