Cosmology with x-matter

Takeshi Chiba; Naoshi Sugiyama; Takashi Nakamura

doi:10.1093/mnras/289.2.L5

paper

Cosmology with x-matter

arXiv:astro-ph/9704199 · doi:10.1093/mnras/289.2.L5

Abstract

Motivated by the possibility of $H_{0} t_{0} > 1$ where $H_{0}$ and $t_{0}$ are the Hubble parameter and the age of the universe, respectively, we investigate the cosmology including x-matter. x-matter is expressed by the equation of state $p_{x} = w_{0} ρ_{x 0} + c_{s}^{2} (ρ_{x} - ρ_{x 0})$ , where $p_{x}$ , $ρ_{x}$ and $ρ_{x 0}$ are the pressure, the density of x-matter and the density at present, respectively. $w_{0}$ and $c_{s}^{2}$ are functions of $ρ_{x}$ in general. x-matter has the most general form of the equation of state which is characterized by 1)violation of strong energy condition at present for $w_{0} < - 1/3$ ; 2) locally stable (i.e. $c_{s}^{2} \geq 0$ ); 3)causality is guaranteed ( $c_{s} \leq 1$ ). Considering the case that $w_{0}$ and $c_{s}^{2}$ are constants, we find that there is a large parameter space of $(w_{0}, c_{s}^{2}, Ω_{x 0})$ in which the model universe is consistent with the age of the universe and the observations of distant Type I supernovae.

minor changes, 4 pages, 6 figures, accepted for publication as a Letter in MNRAS

Cosmology with x-matter

Abstract

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