Cosmic microwave background limits on spatially homogeneous cosmological models with a cosmological constant

We investigate the effect of dark energy on the limits on the shear anisotropy in spatially homogeneous Bianchi cosmological models obtained from measurements of the temperature anisotropies in the cosmic microwave background. We shall primarily assume that the dark energy is modelled by a cosmological constant. In general, we find that there are tighter bounds on the shear than in models with no cosmological constant, although the limits are ( Bianchi) model dependent. In addition, there are special spatially homogeneous cosmological models whose rate of expansion is highly anisotropic, but whose cosmic microwave background temperature is measured to be exactly isotropic at one instant of time.