Open AccessLinear perturbations in a universe with a cosmological constant
Author(s) -
Vale António,
Lemos José P. S.
Publication year - 2001
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2001.04542.x
Subject(s) - physics , cosmological constant , quintessence , de sitter universe , dark energy , perfect cosmological principle , metric expansion of space , lambda cdm model , universe , equation of state , cosmology , classical mechanics , astrophysics , quantum mechanics
There is now evidence that the cosmological constant Λ has a non‐zero positive value. Alternative scenarios to a pure cosmological constant model are provided by quintessence, an effective negative pressure fluid permeating the Universe. Recent results indicate that the energy density ρ and the pressure p of this fluid are constrained by −ρ≤p≲−0.6ρ . As p=−ρ is equivalent to the pure cosmological constant model, it is appropriate to analyse this particular, but important, case further. We study the linear theory of perturbations in a Friedmann–Robertson–Walker universe with a cosmological constant. We obtain the equations for the evolution of the perturbations in the fully relativistic case, for which we analyse the single‐fluid and two‐fluid cases. We obtain solutions to these equations in appropriate limits. We also study the Newtonian approximation. We find that for a positive cosmological constant universe (i) the perturbations will grow more slowly in the relativistic regime for a two‐fluid composed of dark matter and radiation, and (ii) in the Newtonian regime the perturbations stop growing.