Early Universe in Scalar-Tensor Theory

Abstract

We consider the flat Robertson–Walker model in scalar-tensor theory proposed by Lau and Prokhovnik. In this model, the field equations are solved by using “gamma-law” form of equation of state p=(γ−1)ρ, where the adiabatic parameter ‘gamma’ (γ) varies continuously as the universe expands. Our aim is to study how the adiabatic parameter γ should vary so that in the course of its evolution the universe goes through a transition from an inflationary to a radiation-dominated phase. A unified one parameter function of γ has been considered to describe the two early phases of evolution of universe. The solutions show the power-law expansion and cosmological constant is found to be positive and decreasing function of cosmic time. The solutions are compatible with the Dirac’s large number hypothesis. The deceleration parameter has been presented in a unified manner in terms of scale factor, which describes the inflation of the model. The nature of singularity and the physical properties have been discussed in details.