Non-Gaussian CMB and LSS statistics beyond polyspectra

Abstract: Cosmic inflation may have led to non-Gaussian initial conditions that cannot be fully parametrised by 3- and/or 4-point functions. In this work, we discuss various strategies to search for primordial non-Gaussianity beyond polyspectra with the help of cosmological data. Our starting point is a generalised local ansatz for the primordial curvature perturbation $\zeta$ of the form $\zeta = \zeta_{\rm G} + \mathcal{F}{\rm NG} (\zeta{\rm G})$, where $\zeta_{\rm G}$ is a Gaussian random field and $\mathcal{F}{\rm NG}$ is an arbitrary function parametrising non-Gaussianity that, in principle, could be reconstructed from data. Noteworthily, in the case of multi-field inflation, the function $\mathcal{F}{\rm NG}$ can be shown to be determined by the shape of tomographic sections of the landscape potential responsible for driving inflation. We discuss how this generalised local ansatz leads to a probability distribution functional that may be used to extract information about inflation from current and future observations. In particular, we derive various classes of probability distribution functions suitable for the statistical analysis of the cosmic microwave background and large-scale structure.