291 research outputs found
The Effects of Gravitational Back-Reaction on Cosmological Perturbations
Because of the non-linearity of the Einstein equations, the cosmological
fluctuations which are generated during inflation on a wide range of
wavelengths do not evolve independently. In particular, to second order in
perturbation theory, the first order fluctuations back-react both on the
background geometry and on the perturbations themselves. I this paper, the
gravitational back-reaction of long wavelength (super-Hubble) scalar metric
fluctuations on the perturbations themselves is investigated for a large class
of inflationary models. Specifically, the equations describing the evolution of
long wavelength cosmological metric and matter perturbations in an inflationary
universe are solved to second order in both the amplitude of the perturbations
and in the slow roll expansion parameter. Assuming that the linear fluctuations
have random phases, we show that the fractional correction to the power
spectrum due to the leading infrared back-reaction terms does not change the
shape of the spectrum. The amplitude of the effect is suppressed by the product
of the inflationary slow-roll parameter and the amplitude of the linear power
spectrum. The non-gaussianity of the spectrum induced by back-reaction is
commented upon.Comment: 9 page
The initial singularity in solutions of the Einstein-Vlasov system of Bianchi type I
The dynamics of solutions of the Einstein-Vlasov system with Bianchi I
symmetry is discussed in the case of massive or massless particles. It is shown
that in the case of massive particles the solutions are asymptotic to isotropic
dust solutions at late times. The initial singularity is more difficult to
analyse. It is shown that the asymptotic behaviour there must be one of a small
set of possibilities but it is not clear whether all of these possibilities are
realized. One solution is exhibited in the case of massless particles which
behaves quite differently near the singularity from any Bianchi I solution with
perfect fluid as matter model. In particular the matter is not dynamically
negligeable near the singularity for this solution.Comment: 16 page
Absence of a Periodic Component in Quasar z-Distribution
Since the discovery of quasars in papers often appeared and appear the
assertions that the redshift quasar distribution includes a periodic component
with the period or 0.11. A statement of such kind, if it is
correct, may manifest the existence of a far order in quasar distribution in
cosmological time, that might lead to a fundamental revision all the
cosmological paradigm. In the present time there is a unique opportunity to
check this statement with a high precision, using the rich statictics of 2dF
and SDSS catalogues (about 85000 quasars). Our analysis indicates that the
periodic component in distribution of quasar redshifts is absent at high
confidence level
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