Attractor scenarios and superluminal signals in k-essence cosmology

Details Attractor scenarios and superluminal signals in k-essence cosmology Attractor scenarios and superluminal signals in k-essence cosmology

2007-06-27

arxiv.org/abs/0706.3994v2

Phys.Rev.D76:083511,2007

Astronomy and Astrophysics

Astrophysics

General Relativity and Quantum Cosmology

27 pages, RevTeX4. Minor cosmetic changes, references added

Scientific paper

10.1103/PhysRevD.76.083511

Cosmological scenarios with k-essence are invoked in order to explain the observed late-time acceleration of the universe. These scenarios avoid the need for fine-tuned initial conditions (the "coincidence problem") because of the attractor-like dynamics of the k-essence field \phi. It was recently shown that all k-essence scenarios with Lagrangians p=L(X)/\phi^2, necessarily involve an epoch where perturbations of \phi propagate faster than light (the "no-go theorem"). We carry out a comprehensive study of attractor-like cosmological solutions ("trackers") involving a k-essence scalar field \phi and another matter component. The result of this study is a complete classification of k-essence Lagrangians that admit asymptotically stable tracking solutions, among all Lagrangians of the form p=K(\phi)L(X) . Using this classification, we select the class of models that describe the late-time acceleration and avoid the coincidence problem through the tracking mechanism. An analogous "no-go theorem" still holds for this class of models, indicating the existence of a superluminal epoch. In the context of k-essence cosmology, the superluminal epoch does not lead to causality violations. We discuss the implications of superluminal signal propagation for possible causality violations in Lorentz-invariant field theories.

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