The shape of non-Gaussianities

Abstract

We study the dependence on the configuration in momentum space of the primordialthree-point function of density perturbations in several different scenarios: standardslow-roll inflation, curvaton and variable decay models, ghost inflation, models withhigher derivative operators and the DBI model of inflation. We define a cosinebetween the distributions using a measure based on the ability of experiments todistinguish between them. We find that models fall into two broad categorieswith fairly orthogonal distributions: models where non-Gaussianity is created oncrossing the horizon during inflation and models in which the evolution beyondthe horizon dominates. In the first case the three-point function is largest forequilateral triangles, while in the second the dominant contribution to the signal comesfrom the influence of long wavelength modes on small wavelength ones. We showthat, because the distributions in these two cases are so different, translatingconstraints on parameters of one model to those of the other on the basis of thenormalization of the three-point function for equilateral triangles can be very misleading.