The Effective Theory of Quintessence: the w<-1 Side Unveiled

Details The Effective Theory of Quintessence: the w<-1 Side Unveiled The Effective Theory of Quintessence: the w<-1 Side Unveiled

2008-11-05

arxiv.org/abs/0811.0827v3

JCAP 0902:018,2009

Astronomy and Astrophysics

Astrophysics

35 pages, 5 figures, v3: minor modifications, JCAP published version

Scientific paper

10.1088/1475-7516/2009/02/018

We study generic single-field dark energy models, by a parametrization of the most general theory of their perturbations around a given background, including higher derivative terms. In appropriate limits this approach reproduces standard quintessence, k-essence and ghost condensation. We find no general pathology associated to an equation of state w_Q < -1 or in crossing the phantom divide w_Q = -1. Stability requires that the w_Q < -1 side of dark energy behaves, on cosmological scales, as a k-essence fluid with a virtually zero speed of sound. This implies that one should set the speed of sound to zero when comparing with data models with w_Q < -1 or crossing the phantom divide. We summarize the theoretical and stability constraints on the quintessential plane (1+w_Q) vs. speed of sound squared.

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