Cosmological perturbations from vector inflation

We analyze the behavior of linear perturbations in vector inflation. In contrast to scalar field inflation, the linearized theory with vector fields contains couplings between scalar, vector, and tensor modes. The perturbations decouple only in the ultraviolet limit, which allows us to carry out the canonical quantization. Superhorizon perturbations can be approximately analyzed due to suppressed mixing between different modes in the small field models. We find that the vector perturbations of the metric decay exponentially, but the scalar and tensor modes could remain weakly coupled throughout the evolution. As a result, vector inflation can produce significant correlations of the scalar and tensor modes in the CMB. For realistic models the effect is rather small, but not negligible.