Primordial Non-Gaussianity of Gravitational Waves in Ho\v{r}ava-Lifshitz
  Gravity
  In this paper, we study 3-point correlation function of primordial
gravitational waves generated in the de Sitter background in the framework of
the general covariant Ho\v{r}ava-Lifshitz gravity with an arbitrary coupling
constant $\lambda$. We find that, at cubic order, the interaction Hamiltonian
receives contributions from four terms built of the 3-dimensional Ricci tensor
$R_{ij}$ of the leaves $t = $ constant. In particular, the 3D Ricci scalar $R$
yields the same $k$-dependence as that in general relativity, but with
different magnitude due to coupling with the $U(1)$ field $A$ and a UV history.
Interestingly, the two terms $R_{ij}R^{ij}$ and
$\left(\nabla^{i}R^{jk}\right)\left(\nabla_{i}R_{jk}\right)$ exhibit peaks at
the squeezed limit. We show that this is due to the effects of the polarization
tensors. The signal generated by the fourth term, $R^i_j R^j_k R^k_i$, favors
the equilateral shape when spins of the three tensor fields are the same, but
peaks in between the equilateral and squeezed limits when spins are mixed. The
consistency with the recently-released Planck observations on non-Gaussianity
is also discussed and is found that $\left(H/M_*\right)^2\left(H/M_{pl}\right)
\le 10^{-8}$, where $M_{*}$ denotes the suppression energy of high-order
operators, $M_{pl}$ the Planck mass, and $H$ the energy of inflation.
