Statistical Anisotropy from Anisotropic Inflation

TL;DR

This paper reviews anisotropic inflation driven by vector fields, highlighting its deviation from the cosmic no-hair conjecture, and discusses how it produces observable statistical anisotropy in primordial fluctuations detectable via the CMB.

Contribution

It demonstrates the generality of anisotropic inflation, derives universal properties, and formulates perturbation theory to connect theory with CMB observations.

Findings

Anisotropic inflation can be realized with vector fields coupled to the inflaton.

It produces statistical anisotropy in primordial fluctuations.

A method to test anisotropic inflation using CMB data is proposed.

Abstract

We review an inflationary scenario with the anisotropic expansion rate. An anisotropic inflationary universe can be realized by a vector field coupled with an inflaton, which can be regarded as a counter example to the cosmic no-hair conjecture. We show generality of anisotropic inflation and derive a universal property. We formulate cosmological perturbation theory in anisotropic inflation. Using the formalism, we show anisotropic inflation gives rise to the statistical anisotropy in primordial fluctuations. We also explain a method to test anisotropic inflation using the cosmic microwave background radiation (CMB).