Astronomy and Astrophysics – Astrophysics
Scientific paper
2007-03-12
Mod.Phys.Lett.A22:2893-2907,2007
Astronomy and Astrophysics
Astrophysics
11 pages LaTeX file, 3 figures. Modified to match the accepted version in Mod. Phys. Lett. A
Scientific paper
10.1142/S0217732307025893
Considering the general Lagrangian of k-essence models, we study and classify them through variables connected to the fluid equation of state parameter w_\kappa. This allows to find solutions around which the scalar field describes a mixture of dark matter and cosmological constant-like dark energy, an example being the purely kinetic model proposed by Scherrer. Making the stronger assumption that the scalar field Lagrangian is exactly constant along solutions of the equation of motion, we find a general class of k-essence models whose classical trajectories directly describe a unified dark matter/dark energy (cosmological constant) fluid. While the simplest case of a scalar field with canonical kinetic term unavoidably leads to an effective sound speed c_s=1, thereby inhibiting the growth of matter inhomogeneities, more general non-canonical k-essence models allow for the possibility that c_s << 1 whenever matter dominates.
Bertacca Daniele
Matarrese Sabino
Pietroni Massimo
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