We calculate the perturbed action , at second and third order , for a massive three-form field minimally coupled to gravity , and use it to explore the observational predictions of three-form inflation .
One intriguing result is that the value of the spectral index is nearly independent of the three-form potential , being fixed solely by the number of e-folds of inflation , with n _ { s } = 0.97 for the canonical number of 60 .
Considering the bispectrum , we employ standard techniques to give explicit results for two models , one of which produces a large non-Gaussianity .
Finally , we confirm our results by employing a duality relating the three-form theory to a non-canonical scalar field theory and explicitly re-computing results in this dual picture .