Anisotropic universe with anisotropic sources

TL;DR

This paper studies the evolution of an anisotropic universe with sources like anisotropic matter, dark matter, and dark energy, analyzing its dynamics, asymptotic behavior, and effects on cosmic microwave background anisotropies.

Contribution

It extends the analysis of Bianchi-I universes by including anisotropic sources and null geodesics, and investigates their impact on cosmic evolution and CMB anisotropies.

Findings

Identification of stable fixed points in anisotropic universe models

Contribution of anisotropic sources to CMB quadrupole

Detection of a preferred cosmic axis consistent with Planck data

Abstract

We analyze the state space of a Bianchi-I universe with anisotropic sources. Here we consider an extended state space which includes null geodesics in this background. The evolution equations for all the state observables are derived. Dynamical systems approach is used to study the evolution of these equations. The asymptotic stable fixed points for all the evolution equations are found. We also check our analytic results with numerical analysis of these dynamical equations. The evolution of the state observables are studied both in cosmic time and using a dimensionless time variable. Then we repeat the same analysis with a more realistic scenario, adding the isotropic (dust like dark) matter and a cosmological constant (dark energy) to our anisotropic sources, to study their co-evolution. The universe now approaches a de~Sitter space asymptotically dominated by the cosmological constant. The cosmic microwave background anisotropy maps due to shear are also generated in this scenario, assuming that the universe contains anisotropic matter along with the usual (dark) matter and vacuum (dark) energy since decoupling. We find that they contribute dominantly to the CMB quadrupole. We also constrain the current level of anisotropy and also search for any cosmic preferred axis present in the data. We use the Union~2 Supernovae data to this extent. An anisotropy axis close to the mirror symmetry axis seen in the cosmic microwave background data from Planck probe is found.