Publication: Cosmology with moving dark energy and the CMB quadrupole
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Publication Date
2007-07-18
Authors
Beltrán Jiménez, José
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American Physical Society
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Abstract
We study the consequences of a homogeneous dark energy fluid having a nonvanishing velocity with respect to the matter and radiation large-scale rest frames. We consider homogeneous anisotropic cosmological models with four fluids (baryons, radiation, dark matter, and dark energy) whose velocities can differ from each other. Performing a perturbative calculation up to second order in the velocities, we obtain the contribution of the anisotropies generated by the fluids motion to the CMB quadrupole and compare with observations. We also consider the exact problem for arbitrary velocities and solve the corresponding equations numerically for different dark energy models. We find that models whose equation of state is initially stiffer than radiation, as for instance some tracking models, are unstable against velocity perturbations, thus spoiling the late-time predictions for the energy densities. In the case of scaling models, the contributions to the quadrupole can be non-negligible for a wide range of initial conditions. We also consider fluids moving at the speed of light (null fluids) with positive energy and show that, without assuming any particular equation of state, they generically act as a cosmological constant at late times. We find the parameter region for which the models considered could be compatible with the measured (low) quadrupole.
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© 2007 The American Physical Society. We would like to thank A. de la Cruz Dombriz for useful comments. This work has been partially supported by DGICYT (Spain) under Project No. FPA 2004-02602 and No. FPA 2005-02327. The latter project has supported J. B. under the grant No. BES-2006-12059 by Ministerio de Educación y Ciencia.
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