Backreaction of superhorizon perturbations in scalar field cosmologies

TL;DR

This paper demonstrates that superhorizon perturbations cannot cause cosmic acceleration in scalar field cosmologies, confirming that acceleration requires a cosmological constant or similar potential, not backreaction effects.

Contribution

It extends previous results to include scalar fields, showing backreaction cannot induce acceleration without a constant potential component.

Findings

Superhorizon backreaction does not drive acceleration in scalar field models.

Acceleration requires a constant or nearly constant scalar potential.

Some proposed models relying on backreaction are ruled out.

Abstract

It has been suggested that the acceleration of the Universe may be due to the backreaction of perturbations to the Friedmann-Robertson-Walker background. For a Universe dominated by cold dark matter, it is known that the backreaction of superhorizon perturbations can not drive acceleration. We extend this result to models with cold dark matter together with a scalar field. We show that the scalar field can drive acceleration only via the standard mechanism of a constant or nearly constant piece of its potential (i.e., a cosmological constant); there is no separate mechanism involving superhorizon backreaction. This rules out some models which have been proposed in the literature.