Cosmo-dynamics and dark energy with non-linear equation of state: a quadratic model

Details Cosmo-dynamics and dark energy with non-linear equation of state: a quadratic model Cosmo-dynamics and dark energy with non-linear equation of state: a quadratic model

2005-12-08

arxiv.org/abs/astro-ph/0512224v1

Phys.Rev.D74:023523,2006

Astronomy and Astrophysics

Astrophysics

25 pages, 21 figures

Scientific paper

10.1103/PhysRevD.74.023523

We investigate the general relativistic dynamics of Robertson-Walker models with a non-linear equation of state (EoS), focusing on the quadratic case P = P_0 + \alpha \rho + \beta \rho^2. This may be taken to represent the Taylor expansion of any arbitrary barotropic EoS, P(\rho). With the right combination of P_0, \alpha and \beta, it serves as a simple phenomenological model for dark energy, or even unified dark matter. Indeed we show that this simple model for the EoS can produce a large variety of qualitatively different dynamical behaviors that we classify using dynamical systems theory. An almost universal feature is that accelerated expansion phases are mostly natural for these non-linear EoS's. These are often asymptotically de Sitter thanks to the appearance of an effective cosmological constant. 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". In a second paper we investigate the effects of the quadratic EoS in inhomogeneous and anisotropic models, focusing in particular on singularities.

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