Anisotropic dark energy: dynamics of the background and perturbations

We investigate cosmologies where the accelerated expansion of the universe is driven by a field with an anisotropic equation of state. We model such scenarios within the Bianchi I framework, introducing two skewness parameters to quantify the deviation of pressure from isotropy. We study the dynamics of the background expansion in these models. A special case of an anisotropic cosmological constant is analyzed in detail. The anisotropic expansion is then confronted with the redshift and angular distribution of the type Ia supernovae. In addition, we investigate the effects on the cosmic microwave background ( CMB) anisotropies for which the main signature appears to be a quadrupole contribution. We find that the two skewness parameters can be very well constrained. Tightest bounds are imposed by the CMB quadrupole, but there are anisotropic models which avoid these bounds completely. Within these bounds, the anisotropy can be beneficial as a potential explanation for various anomalous cosmological observations, especially in the CMB at the largest angles. We also consider the dynamics of linear perturbations in these models. The covariant approach is used to derive the general evolution equations for cosmological perturbations, taking into account imperfect sources in an anisotropic background. The implications for galaxy formation are then studied. These results might help to make contact between the observed anomalies in CMB and large-scale structure and fundamental theories exhibiting Lorentz violation.