Journal Article

Spherical collapse model in dark-energy cosmologies

F. Pace, J.-C. Waizmann and M. Bartelmann

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 406, issue 3, pages 1865-1874
Published in print August 2010 | ISSN: 0035-8711
Published online August 2010 | e-ISSN: 1365-2966 | DOI:
Spherical collapse model in dark-energy cosmologies

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We study the spherical collapse model for several dark-energy scenarios using the fully non-linear differential equation for the evolution of the density contrast within homogeneous spherical overdensities derived from Newtonian hydrodynamics. While mathematically equivalent to the more common approach based on the differential equation for the radius of the perturbation, this approach has substantial conceptual as well as numerical advantages. Among the most important are that no singularities at early times appear, which avoids numerical problems in particular in applications to cosmologies with dynamical and early dark energy, and that the assumption of time-reversal symmetry can easily be dropped where it is not strictly satisfied. We use this approach to derive the two parameters characterizing the spherical-collapse model, i.e. the linear density threshold for collapse δc and the virial overdensity ΔV, for a broad variety of dark-energy models and to reconsider these parameters in cosmologies with early dark energy. We find that, independently of the model under investigation, δc and ΔV are always very close to the values obtained for the standard ΛCDM model, arguing that the abundance of and the mean density within non-linear structures are quite insensitive to the differences between dark-energy cosmologies. Regarding early dark energy, we thus arrive at a different conclusion than some earlier papers, including one from our group, and we explain why.

Keywords: methods: analytical; cosmology: theory; dark energy

Journal Article.  7049 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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