The isotropic attractor solution of axion-SU(2) inflation: Universal isotropization in Bianchi type-I geometry

Kavli Affiliate: Eiichiro Komatsu

| First 5 Authors: Ira Wolfson, Azadeh Maleknejad, Tomoaki Murata, Eiichiro Komatsu, Tsutomu Kobayashi

| Summary:

SU(2) gauge fields coupled to an axion field can acquire an isotropic
background solution during inflation. We study homogeneous but anisotropic
inflationary solutions in the presence of such (massless) gauge fields. A gauge
field in the cosmological background may pose a threat to spatial isotropy. We
show, however, that such models $textit{generally}$ isotropize in Bianchi
type-I geometry, and the isotropic solution is the attractor. Restricting the
setup by adding an axial symmetry, we revisited the numerical analysis
presented in Wolfson (2020). We find that the reported numerical
breakdown in the previous analysis is an artifact of parametrization
singularity. We use a new parametrization that is well-defined all over the
phase space. We show that the system respects the cosmic no-hair conjecture and
the anisotropies always dilute away within a few e-folds.

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