Self-anisotropizing inflationary universe in Horndeski theory and beyond

TL;DR

This paper demonstrates that certain Horndeski theories can naturally lead to anisotropic inflationary universes without the need for anisotropic matter, challenging previous no-hair theorems in general relativity.

Contribution

It introduces the concept of self-anisotropizing inflation within Horndeski theories, showing anisotropic inflation can occur solely due to the scalar field's properties.

Findings

Horndeski theory admits anisotropic inflationary attractors

Anisotropic inflation can occur without anisotropic matter fields

Concrete example with Bianchi type-I universe provided

Abstract

As opposed to Wald's cosmic no-hair theorem in general relativity, it is shown that the Horndeski theory (and its generalization) admits anisotropic inflationary attractors if the Lagrangian depends cubically on the second derivatives of the scalar field. We dub such a solution as a self-anisotropizing inflationary universe because anisotropic inflation can occur without introducing any anisotropic matter fields such as a vector field. As a concrete example of self-anisotropization we present the dynamics of a Bianchi type-I universe in the Horndeski theory.