Back Reaction of Cosmological Perturbations
Abstract
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 backreaction of fluctuations can be described by an effective energymomentum tensor. The issue of coordinate invariance makes the analysis more complicated for scalar fluctuations than for gravitational waves. We show that the backreaction of fluctuations can be described in a diffeomorphisminvariant way. In an inflationary cosmology, the backreaction is dominated by infrared modes. We show that these modes give a contribution to the effective energymomentum tensor of the form of a negative cosmological constant whose absolute value grows in time. We speculate that this may lead to a selfregulating dynamical relaxation mechanism for the cosmological constant. This scenario would naturally lead to a finite remnant cosmological constant with a magnitude corresponding to Ω_{Λ} ~ 1.
 Publication:

COSMO99, International Workshop on Particle Physics and the Early Universe
 Pub Date:
 2000
 DOI:
 10.1142/9789812792129_0031
 arXiv:
 arXiv:hepth/0004016
 Bibcode:
 2000ppeu.conf..198B
 Keywords:

 High Energy Physics  Theory;
 Astrophysics;
 General Relativity and Quantum Cosmology;
 High Energy Physics  Phenomenology
 EPrint:
 9 pages, invited lecture at COSMO99 (ICTP, Trieste, Sept. 27  Oct. 2 1999)