Inflationary Universe with Anisotropic Hair

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.

Comments: 10 pages, 2 figures; an error in abstract corrected; (v2) replaced with version accepted by PRL, title changed from "Hairy Inflation"