An alternative to the cosmological ``concordance model''
Abstract
Precision measurements of the cosmic microwave background by WMAP are believed to have established a flat Lambda dominated universe, seeded by nearly scaleinvariant adiabatic primordial fluctuations. However by relaxing the hypothesis that the fluctuation spectrum can be described by a single power law, we demonstrate that an Einsteinde Sitter universe with zero cosmological constant can fit the data as well as the best concordance model. Moreover unlike a Lambda dominated universe, such an universe has no strong integrated SachsWolfe 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: H_{0} =~ 46 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 (Omega_{X} ~ 0.1) of matter which does not cluster on small scales, e.g. relic neutrinos with mass of order eV or a ``quintessence'' with w ~ 0, 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 Lyalpha forest. We conclude that Einsteinde 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 nonzero cosmological constant.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 December 2003
 DOI:
 10.1051/00046361:20031425
 arXiv:
 arXiv:astroph/0304237
 Bibcode:
 2003A&A...412...35B
 Keywords:

 cosmology: theory;
 cosmology: cosmic microwave background;
 cosmology: large scale structure of Universe;
 cosmology: cosmological parameters;
 Astrophysics;
 High Energy Physics  Phenomenology
 EPrint:
 Revised version, accepted by A&