Escaping the big rip? -: art. no. 005

We discuss dark energy models which might describe effectively the actual acceleration of the universe. More precisely, for a four-dimensional Friedmann-Lemaitre-Robertson-Walker (FLRW) universe we consider two situations. For the first of them, we model dark energy as phantom energy described as a perfect fluid satisfying the equation of state P = (beta - 1)rho (with beta < 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 as 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 as a phantom generalized Chaplygin gas.