Early Universe Sources for Cmb Non-gaussianity

The common belief that the CMB is Gaussian distributed can be directly traced back to the generic assumption that the quantum fluctuations of the inflaton field are placed in the vacuum state 1. Relaxing this assumption might lead to detectable signatures in various astrophysical tests, most interestingly in future CMB and large-scale structure observations. In this note, we study CMB non-Gaussian signatures predicted within inflationary models with non-vacuum initial states for cosmological perturbations. The model incorporates a privileged scale, which implies the existence of a feature in the primordial power spectrum. The model predicts a vanishing three-point correlation function for the CMB temperature anisotropies 2. We here focus on the first non-vanishing moment, the CMB four-point function at zero lag, namely the kurtosis, and compute its expected value for different locations of the primordial feature in the spectrum, as suggested in the literature to conform to observations of large scale structure 3,4.