Parity breaking signatures from a Chern-Simons coupling during
  inflation: the case of non-Gaussian gravitational waves
  Considering high-energy modifications of Einstein gravity during inflation is
an interesting issue. We can constrain the strength of the new gravitational
terms through observations of inflationary imprints in the actual universe. In
this paper we analyze the effects on slow-roll models due to a Chern-Simons
term coupled to the inflaton field through a generic coupling function
$f(\phi)$. A well known result is the polarization of primordial gravitational
waves (PGW) into left and right eigenstates, as a consequence of parity
breaking. In such a scenario the modifications to the power spectrum of PGW are
suppressed under the conditions that allow to avoid the production of ghost
gravitons at a certain energy scale, the so-called Chern-Simons mass $M_{CS}$.
In general it has been recently pointed out that there is very little hope to
efficiently constrain chirality of PGW on the basis solely of two-point
statistics from future CMB data, even in the most optimistic cases. Thus we
search if significant parity breaking signatures can arise at least in the
bispectrum statistics. We find that the tensor-tensor-scalar bispectra $\langle
\gamma \gamma \zeta \rangle$ for each polarization state are the only ones that
are not suppressed. Their amplitude, setting the level of parity breaking
during inflation, is proportional to the second derivative of the coupling
function $f(\phi)$ and they turn out to be maximum in the squeezed limit. We
comment on the squeezed-limit consistency relation arising in the case of
chiral gravitational waves, and on possible observables to constrain these
signatures.
