Volume 412, Number 1, December II 2003
|Page(s)||35 - 44|
|Section||Cosmology (including clusters of galaxies)|
|Published online||25 November 2003|
An alternative to the cosmological “concordance model”
Laboratoire d'Astrophysique de l'Observatoire Midi-Pyrénées, 14 avenue E. Belin, 31400 Toulouse, France
2 Astrophysics, University of Oxford, Dennis Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
3 Astrophysics Group, Imperial College, Blackett Laboratory, Prince Consort Road, London SW7 2BW, UK
4 Theoretical Physics, University of Oxford, 1 Keble Road, Oxford OX1 3NP, UK
Corresponding author: A. Blanchard, Alain.Blanchard@ast.obs-mip.fr
Accepted: 30 July 2003
Precision measurements of the cosmic microwave background by WMAP are believed to have established a flat Λ-dominated universe, seeded by nearly scale-invariant adiabatic primordial fluctuations. However by relaxing the hypothesis that the fluctuation spectrum can be described by a single power law, we demonstrate that an Einstein-de Sitter universe with zero cosmological constant can fit the data as well as the best concordance model. Moreover unlike a Λ-dominated universe, such an universe has no strong integrated Sachs-Wolfe effect, so is in better agreement with the low quadrupole seen by WMAP. The main concern is that the Hubble constant is required to be rather low: km s-1 Mpc-1; we discuss whether this can be consistent with observations. Furthermore for universes consisting only of baryons and cold dark matter, the amplitude of matter fluctuations on cluster scales is too high, a problem which seems generic. However, an additional small contribution () of matter which does not cluster on small scales, e.g. relic neutrinos with mass of order eV or a “quintessence” with , can alleviate this problem. Such models provide a satisfying description of the power spectrum derived from the 2dF galaxy redshift survey and from observations of the Ly-α forest. We conclude that Einstein-de Sitter models can indeed accommodate all data on the large scale structure of the Universe, hence the Hubble diagram of distant type Ia supernovae remains the only direct evidence for a non-zero cosmological constant.
Key words: cosmology: theory / cosmology: cosmic microwave background / cosmology: large scale structure of Universe / cosmology: cosmological parameters
© ESO, 2003
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