Abstract
The Cosmological Principle asserts that on sufficiently large scales the
universe is homogeneous and isotropic on spatial slices. Challenging this
principle requires a departure from the FLRW ansatz. In this paper we analyse
the cosmological evolution of spatially homogeneous but anisotropic universes
in which only two of the three space dimensions are maximally symmetric, namely
the closed Kantowski-Sachs universe and the open axisymmetric Bianchi type III
universe. These models are characterised by two scale factors and we study
their evolution in universes with radiation, matter and a cosmological
constant. In all cases, the two scale factors evolve differently and this
anisotropy leads to a lensing effect in the propagation of light. We derive
explicit formulae for computing redshifts, angular diameter distances and
luminosity distances and discuss the predictions of these models in relation to
observations for type Ia supernovae and the CMB.
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