UMN-TH-3219/13\

[**Gauge-flation confronted with Planck** ]{}\
[ [**Ryo Namba , Emanuela Dimastrogiovanni , Marco Peloso** ]{} ]{}\
School of Physics and Astronomy, University of Minnesota, Minneapolis, 55455, USA\

[**Abstract**]{}

> Gauge-flation is a recently proposed model in which inflation is driven solely by a non-Abelian gauge field thanks to a specific higher order derivative operator. The nature of the operator is such that it does not introduce ghosts. We compute the cosmological scalar and tensor perturbations for this model, improving over an existing computation. We then confront these results with the Planck data. The model is characterized by the quantity $\gamma \equiv \frac{g^2 Q^2}{H^2}$ (where $g$ is the gauge coupling constant, $Q$ the vector vev, and $H$ the Hubble rate). For $\gamma < 2$, the scalar perturbations show a strong tachyonic instability. In the stable region, the scalar power spectrum $n_s$ is too low at small $\gamma$, while the tensor-to-scalar ratio $r$ is too high at large $\gamma$. No value of $\gamma$ leads to acceptable values for $n_s$ and $r$, and so the model is ruled out by the CMB data. The same behavior with $\gamma$ was obtained in Chromo-natural inflation, a model in which inflation is driven by a 