Astrophysics, abstract
astro-ph/0506534

From: Sabino Matarrese [view email]

Date (v1): Wed, 22 Jun 2005 12:14:08 GMT (27kb)

Date (revised v2): Thu, 22 Jun 2006 13:23:30 GMT (28kb)

On cosmic acceleration without dark energy

Authors: E.W. Kolb (Fermilab and University of Chicago), S. Matarrese (Physics Dept., Padova), A. Riotto (INFN, Padova)

Comments: 33 pages, LaTeX file. Revised to match the final version accepted for publication in NJP

Report-no: FERMILAB-PUB-05-242-A

We elaborate on the proposal that the observed acceleration of the Universe is the result of the backreaction of cosmological perturbations, rather than the effect of a negative-pressure dark-energy fluid or a modification of general relativity. Through the effective Friedmann equations describing an inhomogeneous Universe after smoothing, we demonstrate that acceleration in our local Hubble patch is possible even if fluid elements do not individually undergo accelerated expansion. This invalidates the no-go theorem that there can be no acceleration in our local Hubble patch if the Universe only contains irrotational dust. We then study perturbatively the time behavior of general-relativistic cosmological perturbations, applying, where possible, the renormalization group to regularize the dynamics. We show that an instability occurs in the perturbative expansion involving sub-Hubble modes. Whether this is an indication that acceleration in our Hubble patch originates from the backreaction of cosmological perturbations on observable scales requires a fully non-perturbative approach.

http://arxiv.org/abs/astro-ph/0506534