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Attractor scenarios and superluminal signals in k-essence cosmology

Jin U Kang1,2, Vitaly Vanchurin2, and Sergei Winitzki2

  • 1Department of Physics, Kim Il Sung University, Pyongyang, Democratic People’s Republic of Korea
  • 2Arnold Sommerfeld Center, Department of Physics, Ludwig-Maximilians University, Theresienstrasse 37, 80333 Munich, Germany

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Phys. Rev. D 76, 083511 – Published 15 October, 2007

DOI: https://doi.org/10.1103/PhysRevD.76.083511

Abstract

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 attractorlike dynamics of the k-essence field ϕ. It was recently shown that all k-essence scenarios with Lagrangians p=L(X)ϕ−2, where X≡12ϕ,μϕ,μ, necessarily involve an epoch where perturbations of ϕ propagate faster than light (the “no-go theorem”). We carry out a comprehensive study of attractorlike cosmological solutions (“trackers”) involving a k-essence scalar field ϕ 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(ϕ)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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Phys. Rev. D 76, 083511– Published 15 October, 2007
  • Received 28 June 2007

© 2007 American Physical Society

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