Multiple kinetic k-essence, phantom barrier crossing and stability

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Sur, Sourav
Das, Saurya
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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 wX 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 cX of the dark energy density perturbations may become imaginary while the wX = −1 barrier is crossed. Working out the expression for cX we show that multiple kinetic k-essence fields do indeed lead to a wX = −1 crossing dark energy model, satisfying the stability criterion c2 X ≥ 0 as well as the condition cX ≤ 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 cX 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 wX crosses −1 at red-shift z ∼ 0.2, whereas the dark energy density nearly tracks the matter density at higher red-shifts.
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Dark energy , Kinetic k-essence , Phantom barrier , Stability , Dark energy theory , Supernova type Ia , Cosmological perturbation theory
Sur, S., & Das, S. (2009). Multiple kinetic k-essence, phantom barrier crossing and stability. Journal of Cosmology and Astroparticle Physics, 2009(01), 007.