Primordial tensor non-Gaussianities from general single-field inflation
  with non-Bunch-Davies initial states
  It has been found that the primordial non-Gaussianity of the curvature
perturbation in the case of non-Bunch-Davies initial states can be enhanced
compared with those in the case of the Bunch-Davies one due to the interactions
among the perturbations on subhorizon scales. The purpose of the present paper
is to investigate whether tensor non-Gaussianities can also be enhanced or not
by the same mechanism. We consider general gravity theory in the presence of an
inflaton, and evaluate the tensor auto-bispectrum and the cross-bispectrum
involving one tensor and two scalar modes with the non-Bunch-Davies initial
states for tensor modes. The crucial difference from the case of the scalar
auto-bispectrum is that the tensor three-point function vanishes at the
flattened momentum triangles. We point out that the cross-bispectrum can
potentially be enhanced at non-trivial triangle shapes due to the
non-Bunch-Davies initial states.
