On cosmic acceleration without dark energy

Details On cosmic acceleration without dark energy On cosmic acceleration without dark energy

2005-06-22

arxiv.org/abs/astro-ph/0506534v2

NewJ.Phys.8:322,2006

Astronomy and Astrophysics

Astrophysics

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

Scientific paper

10.1088/1367-2630/8/12/322

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.

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