• DOI:10.1142/9789812792129_0031
• Corpus ID: 119511215

Back Reaction of Cosmological Perturbations

@article{Brandenberger2000BackRO,
  title={Back Reaction of Cosmological Perturbations},
  author={Robert Brandenberger},
  journal={arXiv: High Energy Physics - Theory},
  year={2000},
  pages={198-206}
}

• R. Brandenberger
• Published 4 April 2000
• Physics
• arXiv: High Energy Physics - Theory

The presence of cosmological perturbations affects the background metric and matter configuration in which the perturbations propagate. This effect, studied a long time ago for gravitational waves, also is operational for scalar gravitational fluctuations, inhomogeneities which are believed to be more important in inflationary cosmology. The back-reaction of fluctuations can be described by an effective energy-momentum tensor. The issue of coordinate invariance makes the analysis more complicated for scalar fluctuations than for gravitational waves. We show that the back-reaction of fluctuations can be described in a diffeomorphism-invariant way. In an inflationary cosmology, the back-reaction is dominated by infrared modes. We show that these modes give a contribution to the effective energy-momentum tensor of the form of a negative cosmological constant whose absolute value grows in time. We speculate that this may lead to a self-regulating dynamical relaxation mechanism for the cosmological constant. This scenario would naturally lead to a finite remnant cosmological constant with a magnitude corresponding to $\Omega_{\Lambda} \sim 1$.