Unified cosmology with scalar\u2013tensor theory of gravity

Behzad Tajahmad,Abhik Kumar Sanyal

doi:10.1140/epjc/s10052-017-4785-x

Abstract

Unlike the Noether symmetry, a metric independent general conserved current exists for non-minimally coupled scalar–tensor theory of gravity if the trace of the energy-momentum tensor vanishes. Thus, in the context of cosmology, a symmetry exists both in the early vacuum and radiation dominated era. For slow roll, symmetry is sacrificed, but at the end of early inflation, such a symmetry leads to a Friedmann-like radiation era. Late-time cosmic acceleration in the matter dominated era is realized in the absence of symmetry, in view of the same decayed and redshifted scalar field. Thus, unification of early inflation with late-time cosmic acceleration with a single scalar field may be realized.

Highlights

A smooth luminosity-distance versus redshift curve of the distant SN1a supernovae results in apparent dimming of the supernovae than usual [1,2,3]
The cosmic scale factor must behave lik√e the Friedmann–Lemaitre standard model solution (a ∝ t)
In the pure radiation era if the scale factor a ∝ t, i.e. if the universe evolves like a standard Friedmann solution, only standard nucleosynthesis and structure formation are realized

Summary

Introduction

A smooth luminosity-distance versus redshift curve of the distant SN1a supernovae results in apparent dimming of the supernovae than usual [1,2,3]. For a non-minimally coupled scalar–tensor theory of gravity, a metric independent conserved current is admissible directly from the field equations in general, which is not realized from Noether symmetry [33,34,35,36]. Such a conserved current has been found to play a very important role in generating solutions, even for a higher order theory of gravity [34,35,36] In view of such a symmetry, here we show that the same non-minimally coupled scalar field can possibly drive the inflation at the very early stage of cosmic evolution, and it decays (slowly) in the process, it explains a late-time cosmological behaviour with extremely good precision as well

The model and the symmetry

Early universe

Radiation era

Matter dominated era

Conclusion