The inflationary prediction for primordial non-gaussianity

Abstract

We extend the \delta N formalism so that it gives all of the stochastic properties of the primordial curvature perturbation \zeta if the initial field perturbations are gaussian. The calculation requires only the knowledge of some family of unperturbed universes. A formula is given for the normalisation \fnl of the bispectrum of \zeta, which is the main signal of non-gaussianity. Examples of the use of the formula are given, and its relation to cosmological perturbation theory is explained.

Comments: Revtex Latex file. 4 pages, no figures. v4: minor changes, typos corrected, references added and updated. Version published in Physical Review Letters