New shape of parity-violating graviton non-Gaussianity

We show that the general vacuum states that respect the de Sitter symmetry, known as the α-vacua, can introduce non-vanishing parity-violating tensor non-Gaussianities. This is due to the mixing by the Bogoliubov transformation of the positive and negative frequency modes of the Bunch-Davies vacuum. We calculate explicitly the bispectra of tensor perturbations and show that the amplitude can be exponentially enhanced for certain choices of the squeezing parameter α and the phase ϕ of the α-vacua. We find a new shape for the parity-violating tensor bispectrum which peaks in the flattened configuration.