Spatially Homogeneous Universes with Late-Time Anisotropy

TL;DR

This paper investigates anisotropic cosmological models, specifically Kantowski-Sachs and Bianchi type III universes, analyzing their evolution and observational signatures, and explores their potential to explain supernova and CMB data without a cosmological constant.

Contribution

It provides explicit formulas for observational distances in anisotropic universes and discusses their implications for late-time anisotropy explanations of cosmic acceleration.

Findings

Anisotropic models produce lensing effects on light propagation.

Explicit formulas for redshift and distance measures are derived.

Models can potentially explain supernova luminosity distances without dark energy.

Abstract

The cosmological principle asserts that on sufficiently large scales the Universe is homogeneous and isotropic on spatial slices. To deviate from this principle requires a departure from the FLRW ansatz. In this paper we analyze the cosmological evolution of two spatially homogeneous but anisotropic universes, namely the spatially closed Kantowski-Sachs Universe and the open axisymmetric Bianchi type III Universe. These models are characterized 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. We comment on the possibility of explaining the observed luminosity distance plot for type Ia supernovae within the context of cosmologies featuring late-time anisotropy and a vanishing cosmological constant.