An inflationary model with small scalar and large tensor
  nongaussianities
  We study a model of inflation where the scalar perturbations are almost
gaussian while there is sizable (equilateral) nongaussianity in the tensor
sector. In this model, a rolling pseudoscalar gravitationally coupled to the
inflaton amplifies the vacuum fluctuations of a vector field. The vector
sources both scalar and tensor metric perturbations. Both kinds of
perturbations are nongaussian, but, due to helicity conservation, the tensors
have a larger amplitude, so that nongaussianity in the scalar perturbations is
negligible. Moreover, the tensors produced this way are chiral. We study, in
the flat sky approximation, how constraints on tensor nongaussianities affect
the detectability of parity violation in the Cosmic Microwave Background. We
expect the model to feature interesting patterns on nongaussianities in the
polarization spectra of the CMB.
