Planck Trispectrum Constraints on Primordial Non-Gaussianity at Cubic Order
Non-Gaussianity of the primordial density perturbations provides an important measure to constrain models of inflation. At cubic order the non-Gaussianity is captured by two parameters $τ_{\rm NL}$ and $g_{\rm NL}$ that determine the amplitude of the density perturbation trispectrum. Here we report measurements of the kurtosis power spectra of the cosmic microwave background (CMB) temperature as mapped by Planck by making use of correlations between square temperature-square temperature and cubic temperature-temperature anisotropies. In combination with noise simulations, we find the best joint estimates to be $τ_{\rm{NL}}=0.3 \pm 0.9 \times 10^4$ and $g_{\rm{NL}}=-1.2 \pm 2.8 \times 10^5$. If $τ_{\rm NL}=0$, we find $g_{\rm NL}= -1.3\pm 1.8 \times 10^5$.