Narrow Results

The problem of the cosmic coincidence is a longstanding puzzle. This conundrum may be solved by introducing a coupling between the two dark sectors. In this letter, we study a coupled quintessence scenario in which the scalar field evolves in a power law potential and the mass of dark matter particles depends on a power law function of ϕ. It is shown that this scenario has a stable attractor solution and can thus provide a natural solution to the cosmic coincidence problem.

We study the statefinder parameter in the five-dimensional big bounce model, and apply it to differentiate the attractor solutions of quintessence and phantom field. It is found that the evolving trajectories of these two attractor solutions in the statefinder parameters plane are quite different, and that are different from the statefinder trajectories of other dark energy models.

We consider the phantom cosmology with a Lagrangian originated from the nonlinear Born–Infeld type scalar field. This cosmological model can explain the accelerating expansion of the universe with the equation of state parameter w ≤ -1. We get a sufficient condition for an arbitrary potential that admits a late time attractor solution: the value of potential u(X_c) at the critical point (X_c, 0) should be maximum and greater than zero. We study a specific potential with the form of via phase plane analysis and compute the cosmological evolution by numerical analysis in detail. The results show that the phantom field survives till today (to account for the present observed accelerating expansion) without interfering with the nucleosynthesis of the standard model (the density parameter Ω_ϕ≃10^-12 at the equipartition epoch), and also avoid the future collapse of the universe.

In this paper, we study the cosmological dynamics of dilatonic dark energy model and its phantom model — with negative kinetic energy. When the potential is taken as the form , we investigate the existence of a late time attractor solution, and find out the sufficient condition. One interesting feature found by us is that the evolutions of components of comic density are locally fluctuating on the way to the late time attractor. But this local fluctuation cannot hold the trend that the equation of state ω evolves to -1 and the cosmic density parameter Ω_σ evolves to 1, which are important features for a dark energy model that can meet the current observations.