## 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(Xe^{λφ}), 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 w_{φ} 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 Ω_{φ} satisfying 0 < Ω_{φ} < 1 or a scalar-field dominant solution with Ω_{φ} ≤ 1.

Original language | English |
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Pages (from-to) | 101-129 |

Number of pages | 29 |

Journal | Journal of Cosmology and Astroparticle Physics |

Issue number | 6 |

DOIs | |

Publication status | Published - 2005 Jun 1 |

Externally published | Yes |

## Keywords

- Dark energy theory
- String theory and cosmology

## ASJC Scopus subject areas

- Astronomy and Astrophysics