Coupled dark energy: towards a general description of the dynamics

Gumjudpai, Burin ; Naskar, Tapan ; Sami, M. ; Tsujikawa, Shinji (2005) Coupled dark energy: towards a general description of the dynamics Journal of Cosmology and Astroparticle Physics, 2005 (6). No. pp. given. ISSN 1475-7516

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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 χ =−gμνμϕ∂νϕ/2, 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 (Ωϕ = 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.

Item Type:Article
Source:Copyright of this article belongs to Institute of Physics.
Keywords:String Theory; Cosmology; Dark Energy Theory
ID Code:70520
Deposited On:19 Nov 2011 11:30
Last Modified:19 Nov 2011 11:30

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