Physics – High Energy Physics – High Energy Physics - Theory
Scientific paper
2010-07-31
JCAP 1010:026,2010
Physics
High Energy Physics
High Energy Physics - Theory
41 pages, 7 figures. References and some clarifying language added. This version was accepted for publication in JCAP
Scientific paper
10.1088/1475-7516/2010/10/026
We introduce a large class of scalar-tensor models with interactions containing the second derivatives of the scalar field but not leading to additional degrees of freedom. These models exhibit peculiar features, such as an essential mixing of scalar and tensor kinetic terms, which we have named kinetic braiding. This braiding causes the scalar stress tensor to deviate from the perfect-fluid form. Cosmology in these models possesses a rich phenomenology, even in the limit where the scalar is an exact Goldstone boson. Generically, there are attractor solutions where the scalar monitors the behaviour of external matter. Because of the kinetic braiding, the position of the attractor depends both on the form of the Lagrangian and on the external energy density. The late-time asymptotic of these cosmologies is a de Sitter state. The scalar can exhibit phantom behaviour and is able to cross the phantom divide with neither ghosts nor gradient instabilities. These features provide a new class of models for Dark Energy. As an example, we study in detail a simple one-parameter model. The possible observational signatures of this model include a sizeable Early Dark Energy and a specific equation of state evolving into the final de-Sitter state from a healthy phantom regime.
Deffayet Cédric
Pujolas Oriol
Sawicki Ignacy
Vikman Alexander
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