2007/06/28 by Jin U Kang, Vitaly Vanchurin, Sergei Winitzki · 4 citations
Physics and Astronomy · #Black Holes and Theoretical Physics #Cosmology and Gravitation Theories #Noncommutative and Quantum Gravity Theories #astro-ph #gr-qc #hep-ph #hep-th
paper · pdf · doi:10.1103/physrevd.76.083511
published as Phys.Rev.D76:083511,2007 · 27 pages, RevTeX4. Minor cosmetic changes, references added
arxiv created 2007/06/28 · openalex publication_date 2007/10/15 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
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 \ensuremathφ. It was recently shown that all k-essence scenarios with Lagrangians p=L(X)\ensuremathφ^\ensuremath-2, where X\ensuremath≡(1)/(2)\ensuremathφ_,\ensuremathμ\ensuremathφ^,\ensuremathμ, necessarily involve an epoch where perturbations of \ensuremathφ 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 \ensuremathφ 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(\ensuremathφ)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.