Non-singular Brans-Dicke cosmology with cosmological constant

TL;DR

This paper explores a Brans-Dicke cosmological model with a negative w parameter and a cosmological constant, revealing a bounce that avoids the initial singularity, differing from standard cosmology.

Contribution

It introduces a new solution for Brans-Dicke cosmology with negative w, showing a non-singular bounce in the universe's evolution, extending previous positive-w analyses.

Findings

The universe can undergo a bounce, avoiding initial singularity.

The solution is valid for dust-filled universes, not hot early stages.

Provides qualitative insights for initial conditions of the hot universe.

Abstract

We consider Brans-Dicke cosmology with cosmological constant with negative w parameter and an arbitrary (in general non-vanishing) scale factor at the Big Bang. The field equations describe the flat universe, current observational values for Hubble constant H and deceleration parameter q play a role of initial conditions. In order to solve field equations we adopt the approach of Uehara and Kim (1982). They considered only positive values of w, hence our solution is a new one and has not been described in their paper. Our main result is that unlike the standard cosmology the scale factor may not vanish in it's evolution back in time. In other words our model displays a cosmological bounce and avoids the initial singularity. The formula for the scale factor, leading to the bounce, is only valid for the dust-filled universe and hence cannot be adequate for the hot stage in the early universe when the bounce happens. So, the results of this paper are only qualitative in nature and must be used to obtain initial values for the hot stage of the unverse when one considers the evolution back in time.