A comparison of perturbations in fluid and scalar field models of dark energy

Abstract

We compare perturbations in a fluid model of dark energy with those in a scalar field. As compared to the $\Lambda$CDM model, large scale matter power spectrum is suppressed in fluid model as well as in a generic quintessence dark energy model.To check the efficacy of fluid description of dark energy in emulating a scalar field, we consider a potential which gives the same background evolution as a fluid with a constant equation of state. We show that for sub-Hubble scales, a fluid model effectively emulates a scalar field model. At larger scales, where dark energy perturbations may play a significant role, the fluid analogy breaks down and the evolution of matter density contrast depends on individual scalar field models.

Revtex, 4 pages, 3 postscript figures, minor revisions, figures modified, references added, Phys. Rev. D (in press)

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• Non-linear spherical collapse in tachyon models, and a comparison of collapse in tachyon and quintessence models of dark energy
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