Escaping the big rip?

Abstract

We discuss dark energy models which might describe effectively the actual acceleration of the universe. More precisely, for a 4-dimensional Friedmann-Lemaître-Robertson-Walker (FLRW) universe we consider two situations: First of them, we model dark energy by phantom energy described by a perfect fluid satisfying the equation of state P = (β − 1)ρ (with β < 0 and constant). In this case the universe reaches a "Big Rip" independently of the spatial geometry of the FLRW universe. In the second situation, the dark energy is described by a phantom (generalized) Chaplygin gas which violates the dominant energy condition. Contrary to the previous case, for this material content a FLRW universe would never reach a "big rip" singularity (indeed, the geometry is asymptotically de Sitter). We also show how this dark energy model can be described in terms of scalar fields, corresponding to a minimally coupled scalar field, a Born-Infeld scalar field and a generalized Born-Infeld scalar field. Finally, we introduce a phenomenologically viable model where dark energy is described by a phantom generalized Chaplygin gas. PACS numbers: 98.80.-k,98.80.Es,11.10.-z PU-ICG-04/09, astro-ph/0404540 * Electronic address: mariam.bouhmadi@port.ac.uk † Electronic address: madrid@iaa.es 1 We would like to mention that there are other candidates for dark energy based on brane-world models [15] and modified 4dimensional Einstein-Hilbert actions[16], where a late time acceleration of the universe may be achieved.

Cosmological dynamics and dark energy with a nonlinear equation of state: A quadratic model

“…It is interesting to note that unlike the standard GR case the phantom behavior does not result in a Type I singularity but asymptotically evolves to a expanding de Sitter phase. This is similar to the behavior seen in the phantom generalized Chaplygin gas case [39]. such models to give:…”

“…This suggests that an EoS with the right combination of P 0 , α and β may provide a good and simple phenomenological model for UDM, or at least for a dark energy component. Other interesting possibilities that arise from the quadratic EoS are closed models that can oscillate with no singularity, models that bounce between infinite contraction/expansion and models which evolve from a phantom phase, asymptotically approaching a de Sitter phase instead of evolving to a "big rip" or other pathological future states [13,38,39].…”

Avoidance of big rip in phantom cosmology by gravitational back reaction

“…Defining ρ br ≡ τ 0 0 and p br ≡ − 1 3 τ i i and using Eqs. (5,15,16,18,19), the expression for τ µν can be simplified to…”

“…The above conclusions are based upon a constant negative value of w. However, if the value of w could change during the evolution of the universe and then in principle the big rip can be avoided [12]. Attempts have also been made toward avoiding the big rip by modifying the original Caldwell's phantom model [16,17,18,19,20]. Note that it has been argued that a singularity can also develop at a finite future time even if ρ + 3p is positive [21].…”

Stability properties of some perfect fluid cosmological models

“…In what follows, we shall consider only the Chaplygin gas cosmological model with ρ ≥ √ A which is equivalent to the energy dominance requirement that |p| ≤ ρ. The Chaplygin gas with ρ < √ A was considered elsewhere [21,22]. (While this latter case is obviously not apt to the unification of dark energy and dark matter, it could be useful in the context of phantom cosmology [22]).…”