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Title: Stability of phantom k-essence theories

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', w{sub {lambda}}=-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.

Authors:
;  [1];  [2]
  1. Instituto de Fisica, Universidade de Sao Paulo, CP 66318, 05315-970, Sao Paulo (Brazil)
  2. (Brazil)
Publication Date:
OSTI Identifier:
20782626
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. D, Particles Fields; Journal Volume: 73; Journal Issue: 6; Other Information: DOI: 10.1103/PhysRevD.73.063522; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; COSMOLOGY; EQUATIONS OF STATE; HAMILTONIANS; NONLUMINOUS MATTER; SOUND WAVES; STABILITY; VELOCITY

Citation Formats

Abramo, L. Raul, Pinto-Neto, Nelson, and ICRA-Centro Brasileiro de Pesquisas Fisicas, R. Xavier Sigaud 150, 22290-180, Rio de Janeiro. Stability of phantom k-essence theories. United States: N. p., 2006. Web. doi:10.1103/PHYSREVD.73.063522.
Abramo, L. Raul, Pinto-Neto, Nelson, & ICRA-Centro Brasileiro de Pesquisas Fisicas, R. Xavier Sigaud 150, 22290-180, Rio de Janeiro. Stability of phantom k-essence theories. United States. doi:10.1103/PHYSREVD.73.063522.
Abramo, L. Raul, Pinto-Neto, Nelson, and ICRA-Centro Brasileiro de Pesquisas Fisicas, R. Xavier Sigaud 150, 22290-180, Rio de Janeiro. Wed . "Stability of phantom k-essence theories". United States. doi:10.1103/PHYSREVD.73.063522.
@article{osti_20782626,
title = {Stability of phantom k-essence theories},
author = {Abramo, L. Raul and Pinto-Neto, Nelson and ICRA-Centro Brasileiro de Pesquisas Fisicas, R. Xavier Sigaud 150, 22290-180, Rio de Janeiro},
abstractNote = {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', w{sub {lambda}}=-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.},
doi = {10.1103/PHYSREVD.73.063522},
journal = {Physical Review. D, Particles Fields},
number = 6,
volume = 73,
place = {United States},
year = {Wed Mar 15 00:00:00 EST 2006},
month = {Wed Mar 15 00:00:00 EST 2006}
}
  • We investigate models of dark energy with purely kinetic multiple k-essence sources that allow for the crossing of the phantom divide line, without violating the conditions of stability. It is known that with more than one kinetic k-field one can possibly construct dark energy models whose equation of state parameter w{sub X} crosses -1 (the phantom barrier) at recent red-shifts, as indicated by the Supernova Ia and other observational probes. However, such models may suffer from cosmological instabilities, as the effective speed of propagation c{sub X} of the dark energy density perturbations may become imaginary while the w{sub X} =more » -1 barrier is crossed. Working out the expression for c{sub X} we show that multiple kinetic k-essence fields do indeed lead to a w{sub X} = -1 crossing dark energy model, satisfying the stability criterion c{sub X}{sup 2} {>=} 0 as well as the condition c{sub X} {<=} 1 (in natural units), which implies that the dark energy is not super-luminal. As a specific example, we construct a phantom barrier crossing model involving three k-fields for which c{sub X} is a constant, lying between 0 and 1. The model fits well with the latest Supernova Ia Union data, and the best fit shows that w{sub X} crosses -1 at red-shift z {approx} 0.2, whereas the dark energy density nearly tracks the matter density at higher red-shifts.« less
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