Horizon problem in a closed universe dominated by fluid with negative pressure

Abstract

We discuss the horizon problem in a universe dominated by fluid with negative pressure. We show that for generally accepted value of nonrelativistic matter energy density parameter $Ω_{m0}<1$, the horizon problem can be solved only if the fluid influencing negative pressure (the so-called ``X'' component) violates the point-wise strong energy condition and if its energy density is sufficiently large $(Ω_{X 0}>1)$. The calculated value of the $Ω_{X0}$ parameter allowing for the solution of the horizon problem is confronted with some recent observational data. Assuming that $p_X/ρ_X<-0.6$ we find that the required amount of the ``X'' component is not ruled out by the supernova limits. Since the value of energy density parameter $Ω_{v0}$ for cosmological constant larger than 1 is excluded by gravitational lensing observations the value of the ratio $p_X/ρ_X$ should lie between the values -1 and -0.6 if the model has to be free of the horizon problem beeing at the same time consistent with observations. The value of $Ω_{X0}+Ω_{m0}$ in the model is consistent with the constraints $0.2<Ω_{\text{tot}}<1.5$ following from cosmic microwave background observations provided that $Ω_{m0}$ is low ($<0.2$).