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 W m0`1 , the horizon problem can be solved only if the fluid influencing negative pressure (the socalled``Xº component) violates the point-wise strong energy condition and if its energy density is sufficiently large W X0 b 1. The calculated value of the W X0 parameter allowing for the solution of the horizon problem is confronted with some recent observational data. Assuming that p X ar X`À 0X6 we find that the required amount of the``Xº component is not ruled out by the supernova limits. Since the value of energy density parameter W v0 for cosmological constant larger than 1 is excluded by gravitational lensing observations the value of the ratio p X ar X should lie between the values À1 and À0X6 if the model has to be free of the horizon problem beeing at the same time consistent with observations. The value of W X0 W m0 in the model is consistent with the constraints 0X2`W tot`1 X5 following from cosmic microwave background observations provided that W m0 is low (`0X2).

An analysis of cosmological perturbations in hydrodynamical and field representations

“…where the overdot denotes the derivative with respect to the time coordinate t. The equations (5,6,7) are not independent due to the Bianchi identities.…”

“…It is a straightforward to check that the equations (5,6,7) and equations (11,12,13) permit the identification…”

“…If the results of the supernova observations are confirmed, the energy of the universe today must be dominated by a fluid with negative pressure. It could be a cosmological constant, but other cases are not excluded, such as a fluid of cosmic string or domain walls [4][5][6] or some scalar field, with a peculiar kind of potential, called quintessence [7][8][9][10][11].…”

Gravitational waves in cosmological models with negative pressure

“…In doing so, we modify the dynamics of the Universe, consequently changing the estimates for the clustered mass and the age of the Universe. In some specific cases, an alternative explanation for the isotropy of the Universe can be implemented [7], if the spatial section is positive. A more recent example is the so-called 'quintessence', a fluid component that would be present in the Universe as well as the ordinary fluid.…”

“…Hence, even if the spacelike surfaces are compact, with k = 1, the scale factor can represent a Universe with eternal expansion; the dynamics of this closed Universe has features similar to the open model where matter has a positive pressure. This can solve the horizon problem without inflation [7]. In [15] the confrontation of specific models with observation has led to some viable scenarios.…”