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On the Stability of Phantom K-essence Theories

L. Raul Abramo, Nelson Pinto-Neto

astro-pharXiv:astro-ph/0511562

Abstract

We show that phantom dark energy, if it is described by a K-essence theory, has three fundamental problems: first, its hamiltonian is unbounded from below. Second, classical stability precludes the equation of state from crossing the ``Lambda-barrier'', wΛ=-1. Finally, both the equation of state and the sound speed are unbounded -- the first, from below, the second, from above -- if the kinetic term is not bounded by dynamics.

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