Large Tensor Non-Gaussianity from Axion-Gauge Fields Dynamics

Abstract

We show that an inflation model in which a spectator axion field is coupled to an SU(2) gauge field produces a large three-point function (bispectrum) of primordial gravitational waves, $B_h$, on the scales relevant to the cosmic microwave background experiments. The amplitude of the bispectrum at the equilateral configuration is characterized by $B_h/P_h^2=\mathcal{O}(10)\times {\Omega }_A^{-1}$, where ${\Omega }_A$ is a fraction of the energy density in the gauge field and $P_h$ is the power spectrum of gravitational waves produced by the gauge field.

6 pages, 2 figures; matches version accepted by PRD