Coupled dark energy: Towards a general description of the dynamics

Burin Gumjudpai, Tapan Naskar, M. Sami, Shinji Tsujikawa

Research output: Contribution to journalArticle

154 Citations (Scopus)

Abstract

In dark energy models of scalar-field coupled to a barotropic perfect fluid, the existence of cosmological scaling solutions restricts the Lagrangian of the field φ to p ≤ Xg(Xeλφ), where , λ is a constant and g is an arbitrary function. We derive general evolution equations in an autonomous form for this Lagrangian and investigate the stability of fixed points for several different dark energy models: (i) ordinary (phantom) field, (ii) dilatonic ghost condensate, and (iii) (phantom) tachyon. We find the existence of scalar-field dominant fixed points (Ω φ ≤ 1) with an accelerated expansion in all models irrespective of the presence of the coupling Q between dark energy and dark matter. These fixed points are always classically stable for a phantom field, implying that the universe is eventually dominated by the energy density of a scalar field if a phantom is responsible for dark energy. When the equation of state wφ for the field φ is larger than -1, we find that scaling solutions are stable if the scalar-field dominant solution is unstable, and vice versa. Therefore in this case the final attractor is either a scaling solution with constant Ωφ satisfying 0 < Ωφ < 1 or a scalar-field dominant solution with Ωφ ≤ 1.

Original languageEnglish
Pages (from-to)101-129
Number of pages29
JournalJournal of Cosmology and Astroparticle Physics
Issue number6
DOIs
Publication statusPublished - 2005 Jun 1
Externally publishedYes

Keywords

  • Dark energy theory
  • String theory and cosmology

ASJC Scopus subject areas

  • Astronomy and Astrophysics

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