Time Evolution of Density Parameters for Matter and Dark Energy and their Interaction Term in Brans-Dicke Gravity

TL;DR

This paper investigates the time evolution of density parameters for matter and dark energy within Brans-Dicke gravity, proposing an interaction term that indicates matter converting into dark energy, and analyzes how scalar field dependence influences cosmic evolution.

Contribution

It introduces a method to determine dark energy evolution without a cosmological constant or self-interaction potential, emphasizing the scalar field's role in cosmological dynamics.

Findings

Negative interaction term at present suggests matter converts into dark energy.

Scalar field dependence critically influences the evolution of cosmological quantities.

The approach models cosmic acceleration and deceleration phases without additional potentials.

Abstract

In the framework of Brans-Dicke (BD) theory, the first part of the present study determines the time dependence of BD parameter, energy density and equation of state (EoS) parameter of the cosmic fluid in a universe expanding with acceleration, preceded by a phase of deceleration. For this purpose, a scale factor has been chosen such that the deceleration parameter, obtained from it, shows a signature flip with time. Considering the dark energy to be responsible for the entire pressure, the time evolution of energy parameters for matter and dark energy and the EoS parameter for dark energy have been determined. An effective interaction term, between matter and dark energy, has been proposed and calculated. Its negative value at the present time indicates conversion of matter into dark energy. Using this term, the time dependence of the rates of change of matter and dark energy has been determined. It is found that the nature of dependence of the scalar field upon the scale factor plays a very important role in governing the time evolution of the cosmological quantities studied here. The present study provides us with a simple way to determine the time evolution of dark energy for a homogeneous and isotropic universe of zero spatial curvature, without involving any self-interaction potential or cosmological constant in the formulation.