Astronomy and Astrophysics – Astrophysics – Cosmology and Extragalactic Astrophysics
Scientific paper
2010-07-05
Phys.Rev.D 82,063507(2010)
Astronomy and Astrophysics
Astrophysics
Cosmology and Extragalactic Astrophysics
19 pages, 6 figures
Scientific paper
We investigate the cosmological perturbation dynamics for a universe consisting of pressureless baryonic matter and a viscous fluid, the latter representing a unified model of the dark sector. In the homogeneous and isotropic background the \textit{total} energy density of this mixture behaves as a generalized Chaplygin gas. The perturbations of this energy density are intrinsically non-adiabatic and source relative entropy perturbations. The resulting baryonic matter power spectrum is shown to be compatible with the 2dFGRS and SDSS (DR7) data. A joint statistical analysis, using also Hubble-function and supernovae Ia data, shows that, different from other studies, there exists a maximum in the probability distribution for a negative present value $q_0 \approx - 0.53$ of the deceleration parameter. Moreover, while previous descriptions on the basis of generalized Chaplygin gas models were incompatible with the matter power spectrum data since they required a much too large amount of pressureless matter, the unified model presented here favors a matter content that is of the order of the baryonic matter abundance suggested by big-bang nucleosynthesis.
Hipólito-Ricaldi Wiliam S.
Velten H. E. S.
Zimdahl Winfried
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