On the Back Reaction Problem for Gravitational Perturbations

TL;DR

This paper derives a gauge-invariant effective energy-momentum tensor for cosmological perturbations and demonstrates that their back reaction can significantly influence the inflationary universe at energies below the self-reproduction scale.

Contribution

It introduces a gauge-invariant formulation of the energy-momentum tensor for perturbations and analyzes their impact on the inflationary background.

Findings

Back reaction becomes significant below the self-reproduction scale.

Perturbations can alter the evolution of the inflationary universe.

The effective energy-momentum tensor is gauge-invariant.

Abstract

We derive the effective energy-momentum tensor for cosmological perturbations and prove its gauge-invariance. The result is applied to study the influence of perturbations on the behaviour of the Friedmann background in inflationary Universe scenarios. We found that the back reaction of cosmological perturbations on the background can become important already at energies below the self-reproduction scale.