On the Chameleon Brans-Dicke Cosmology

TL;DR

This paper explores a generalized Brans-Dicke cosmological model with a scalar field potential and matter coupling, demonstrating conditions for universe acceleration and thermodynamic constraints on energy transfer.

Contribution

It introduces a power-law form for potential and coupling functions, analyzing their roles in cosmic acceleration and energy transfer within Brans-Dicke theory.

Findings

Acceleration occurs for specific potential exponents.

Potential influences universe dynamics more than coupling functions.

Thermodynamics constrains the direction of energy transfer.

Abstract

We consider a generalized Brans-Dicke model in which the scalar field has a potential function and is also allowed to couple non-minimally with the matter sector. We assume a power law form for the potential and the coupling functions as the inputs of the model and show that acceleration of the universe can be realized for a constrained range of exponent of the potential function. We also argue that this accelerating phase is consistent with a large and positive Brans-Dicke parameter. In our analysis, the potential plays a more important role with respect to the coupling function in dynamics of the universe as the latter does not contribute to any of the relations characterizing evolution of scale factor of the universe and the scalar field. However, we will show that the coupling function is closely related to magnitude and direction of the energy transfer between matter and the scale field. We use this fact and some thermodynamic aspects of the model to put some constraints on the coupling function. In particular, we argue that the second law of thermodynamics constrains direction of the overall energy transfer.