Unified Dark Matter scalar field models with fast transition

Details Unified Dark Matter scalar field models with fast transition Unified Dark Matter scalar field models with fast transition

2010-11-30

arxiv.org/abs/1011.6669v3

JCAP02(2011)018

Astronomy and Astrophysics

Astrophysics

Cosmology and Extragalactic Astrophysics

Slightly revised version accepted for publication in JCAP, with a few added references; 27 pages, 13 figures

Scientific paper

10.1088/1475-7516/2011/02/018

We investigate the general properties of Unified Dark Matter (UDM) scalar field models with Lagrangians with a non-canonical kinetic term, looking specifically for models that can produce a fast transition between an early Einstein-de Sitter CDM-like era and a later Dark Energy like phase, similarly to the barotropic fluid UDM models in JCAP1001(2010)014. However, while the background evolution can be very similar in the two cases, the perturbations are naturally adiabatic in fluid models, while in the scalar field case they are necessarily non-adiabatic. The new approach to building UDM Lagrangians proposed here allows to escape the common problem of the fine-tuning of the parameters which plague many UDM models. We analyse the properties of perturbations in our model, focusing on the the evolution of the effective speed of sound and that of the Jeans length. With this insight, we can set theoretical constraints on the parameters of the model, predicting sufficient conditions for the model to be viable. An interesting feature of our models is that what can be interpreted as w_{DE} can be <-1 without violating the null energy conditions.

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