Particle horizon

About: Particle horizon is a research topic. Over the lifetime, 2096 publications have been published within this topic receiving 69137 citations.

Implications of a nonzero cosmological constant and luminosity selection effects on cosmological tests

Abstract: This paper examines the implications of a nonzero cosmological constant Λ 0 on the amount of linear size evolution and the luminosity selection effects usually required in the interpretation of the angular diameter–redshift (θ–z) test. This is based on three typical cases chosen on various plausible assumptions which can be made concerning the contribution of Λ 0 to the density of the universe (parametrised by O0). The results show that a fairly strong linear size evolution will be required to interpret the θ–z data of extended steep spectrum quasars for all three cases, if luminosity effects are neglected. However, this evolution is significantly steeper in a matter-dominated universe with OM = O0 = 1 than in both the flat universe with OΛ = 0·8, OM = 0·2 and an open universe with OM = 0·2, Λ = 0. Furthermore, when the luminosity selection effects present in the sample are considered, a milder size evolution is obtained for the OM = 1, OΛ = 0 model while little or no size evolution is found for the other two cases. There is therefore no significant difference in our results for an open low density universe with OΛ = 0 and a flat universe dominated by OΛ predicted by inflation. The present results therefore imply that an open low density universe with OM = 0·2 and OΛ = 0 is compatible with an inflationary model of the universe with OM = 0·2 and OΛ = 0 · 8. This leads to a contradiction since the universe cannot be open and spatially closed at the same time (the existence of one should preclude the other).

Dynamics of the Cosmological Constant in Two-Dimensional Universe

Abstract: We consider a two-dimensional model of gravity with the cosmological constant as a dynamical variable. The effective cosmological constant is derived when the universe has no initial boundary. It turns out to be extremely small if the universe is sufficiently large

Universality of Final State in Two Dimensional Dilaton Cosmology

Abstract: Two dimensional dilaton gravity theories provide a class of cosmological toy models in which the semiclassical quantum correction is analytically solvable. The most general semiclassical solution describing inhomogeneous universe is discussed, and all the big bang type universe is shown to end in a flat universe with a universally created matter, irrespective of arty irregularities initially present. It is also pointed out that the same universal behavior towards the final stage of universe remains valid to the leading 'Ii order in the nonintegrable model.

Probing the pre-big bang universe

Abstract: Superstring theory suggests a new cosmology whereby a long inflationary phase preceeded a non singular big bang-like event. After discussing how pre-big bang inflation naturally arises from an almost trivial initial state of the Universe, I will describe how present or near-future experiments can provide sensitive probes of how the Universe behaved in the pre-bang era.