A Study of Cosmic Expansion Generated by Non-conservation of Matter in the Framework of Brans-Dicke Theory

TL;DR

This paper explores how matter-dark energy interaction within Brans-Dicke theory can explain cosmic acceleration, showing that matter converts into dark energy over time, affecting the universe's expansion and gravitational constant.

Contribution

It introduces an empirical model of matter-dark energy interaction in Brans-Dicke theory, linking matter conversion to late-time cosmic acceleration and variable gravitational parameters.

Findings

Matter decreases monotonically over time.

Late-time acceleration causes deceleration parameter to turn negative.

Gravitational constant varies with matter-dark energy conversion.

Abstract

The present study, on the expansion of universe, is based on an assumption regarding the possibility of inter-conversion between matter and dark energy, through some interaction of matter with the scalar field in the framework of Brans-Dicke theory. The field equations for a spatially flat space-time have been solved using an empirical dependence of scalar field parameter upon the scale factor. To represent the behaviour regarding the non-conservation of matter, a function, expressed in terms of the Hubble parameter, has been empirically incorporated into the field equations. Their solution shows that, this function, whose value is proportional to the matter content of the universe, decreases monotonically with time. This matter-field interaction generates late time acceleration, causing the deceleration parameter to change its sign from positive to negative. Time dependence of the proportion of dark energy component of the universe has been determined and shown graphically. Time variation of gravitational constant and the Brans-Dicke dimensionless parameter has been analyzed in the present study. The rate of generation of dark energy from matter has been found to affect the time variations of deceleration parameter and gravitational constant.