Inflationary Universe with Anisotropic Hair

TL;DR

This paper explores an inflationary universe model where a vector field causes anisotropy, challenging the cosmic no-hair conjecture and providing insights into observable anisotropic signatures during inflation.

Contribution

It introduces a novel anisotropic inflation model with a vector field, demonstrating a universal relation between anisotropy and slow-roll parameters, and discusses its observational implications.

Findings

Anisotropic inflation occurs over a wide range of coupling functions.

A universal relation links anisotropy to the slow-roll parameter.

The model provides a counterexample to the cosmic no-hair conjecture.

Abstract

We study an inflationary scenario with a vector field coupled with an inflaton field and show that the inflationary universe is endowed with anisotropy for a wide range of coupling functions. This anisotropic inflation is a tracking solution where the energy density of the vector field follows that of the inflaton field irrespective of initial conditions. We find a universal relation between the anisotropy and a slow-roll parameter of inflation. Our finding has observational implications and gives a counter example to the cosmic no-hair conjecture.