EDP Sciences
Free access
Volume 366, Number 2, February I 2001
Page(s) 395 - 406
Section Cosmology
DOI http://dx.doi.org/10.1051/0004-6361:20000103

A&A 366, 395-406 (2001)
DOI: 10.1051/0004-6361:20000103

Classification of multifluid CP world models

J. Thomas and H. Schulz

Astronomisches Institut der Ruhr-Universität, 44780 Bochum, Germany
e-mail: jthomas, hschulz@astro.ruhr-uni-bochum.de

(Received 25 August 2000 / Accepted 14 November 2000 )

Various classification schemes exist for homogeneous and isotropic (CP) world models, which include pressureless matter (so-called dust) and Einstein's cosmological constant $\Lambda$. We here classify the solutions of more general world models consisting of up to four non-interacting fluids, each with pressure ${\cal P}_j$, energy density $\epsilon_j$ and an equation of state ${\cal P}_j = (\gamma_j - 1) \epsilon_j$ with $0 \le \gamma_j \le 2$. In addition to repulsive fluids with negative pressure and positive energy density, which generalize the classical repulsive (positive) $\Lambda$ component, we consider fluids with negative energy density as well. The latter generalize a negative $\Lambda$ component. This renders possible new types of models that do not occur among the classical classifications of world models. Singularity-free periodic solutions as well as further "hill-type", "hollow-type"and "shifting-type"models are feasible. However, if one only allows for three components (dust, radiation and one repulsive component) in a spatially flat universe the repulsive classical $\Lambda$ fluid (with $\Lambda > 0$) tends to yield the smoothest fits of the Supernova Ia data from Perlmutter et al. (1999). Adopting the SN Ia constraints, exotic negative energy density components can be fittingly included only if the universe consists of four or more fluids.

Key words: Cosmology: miscellaneous -- Cosmology: theory

Offprint request: H. Schulz

© ESO 2001