How does SU($N$)-natural inflation isotropize the universe?

TL;DR

This paper investigates how SU(N)-natural inflation models lead to the isotropization of the universe, analyzing gauge field configurations and their evolution, with potential observable signatures in the CMB and gravitational waves.

Contribution

It introduces a method to identify isotropic gauge field configurations in SU(N) inflation and demonstrates universality of isotropization in SU(3), including possible transitions affecting observables.

Findings

Isotropic universe is a late-time attractor for SU(3) gauge fields.

Transitions between different gauge configurations can occur during inflation.

Such transitions may leave observable imprints on CMB and gravitational waves.

Abstract

We study the homogeneous and anisotropic dynamics of pseudoscalar inflation coupled to an SU($N$) gauge field. To see how the initially anisotropic universe is isotropized in such an inflation model, we derive the equations to obtain axisymmetric SU($N$) gauge field configurations in Bianchi type-I geometry and discuss a method to identify their isotropic subsets which are the candidates of their late-time attractor. Each isotropic solution is characterized by the corresponding SU(2) subalgebra of the SU($N$) algebra. It is shown numerically that the isotropic universe is a universal late-time attractor in the case of the SU(3) gauge field. Interestingly, we find that a transition between the two distinct gauge-field configurations characterized by different SU(2) subalgebras can occur during inflation. We clarify the conditions for this to occur. This transition could leave an observable imprint on the CMB and the primordial gravitational wave background.