Primordial non-Gaussianities of general multiple-field inflation

Abstract

We perform a general study of the primordial scalar non-Gaussianities in multi-fieldinflationary models in Einstein gravity. We consider models governed by a Lagrangian which isa general function of the scalar fields and their first-order spacetime derivatives. We useδN formalism to relate scalar fields and the curvature perturbations. We calculatethe explicit cubic order perturbative action and the three-point function ofcurvature perturbation evaluated at the horizon crossing. Under reasonableassumptions, in the small slowly varying parameters limit and with a sound speedcs close to one, we find that the non-Gaussianity is completely determined by these slowlyvarying parameters and some other parameters which are determined by the structure ofthe inflationary model. Our work generalizes previous results, and implies the possibility ofthe existence of large non-Gaussianity in model constructing, and it would be also useful tostudy the non-Gaussianity in multi-field inflationary models which will be constructed inthe future.