Anisotropic cosmologies containing isotropic background radiation

TL;DR

This paper introduces an anisotropic cosmological model with a scalar field and isotropic fluids, aligning with standard cosmology and CMB isotropy, while explaining anisotropy and near-critical density.

Contribution

It presents a new exact solution of Einstein equations incorporating anisotropic scalar fields and isotropic fluids, maintaining standard cosmological evolution and CMB isotropy.

Findings

Model remains quasiflat throughout cosmic history.

Scalar field energy density is close to critical density.

Approximate solutions for shear-free rotating cosmologies are valid within observational bounds.

Abstract

We present an anisotropic cosmological model based on a new exact solution of Einstein equations. The matter content consists of an anisotropic scalar field minimally coupled to gravity and of two isotropic perfect fluids that represent dust matter and radiation. The spacetime is described by a spatially homogeneous, Bianchi type III metric with a conformal expansion. The model respects the evolution of the scale factor predicted by standard cosmology, as well as the isotropy of the cosmic microwave background. Remarkably, the introduction of the scalar field, apart from explaining the spacetime anisotropy, gives rise to an energy density that is close to the critical density. As a consequence, the model is quasiflat during the entire history of the universe. Using these results, we are also able to construct approximate solutions for shear-free cosmological models with rotation. We finally carry out a quantitative discussion of the validity of such solutions, showing that our approximations are acceptably good if the angular velocity of the universe is within the observational bounds derived from rotation of galaxies.