Accelerating cosmologies with an anisotropic equation of state

If the dark energy equation of state is anisotropic, the expansion rate of the universe becomes direction dependent at late times. We show that such models are not only cosmologically viable but that they could explain some of the observed anomalies in the cosmic microwave background. The possible anisotropy can then be constrained by studying its effects on the luminosity distance-redshift relation inferred from several observations. A vector field action for dark energy is also presented as an example of such a possibility.