Non-Gaussianities in two-field inflation

Abstract

We study the bispectrum of the curvature perturbation on uniform energydensity hypersurfaces in models of inflation with two scalar fields evolvingsimultaneously. In the case of a separable potential, it is possible to compute thecurvature perturbation up to second order in the perturbations, generated onlarge scales due to the presence of non-adiabatic perturbations, by employing theδN-formalism, in the slow-roll approximation. In this case, we provide an analytic formula for the nonlinearparameter fNL. We apply this formula to double inflation with two massive fields, showing that it doesnot generate significant non-Gaussianity; the nonlinear parameter at the end of inflation isslow-roll suppressed. Finally, we develop a numerical method for generic two-field models ofinflation, which allows us to go beyond the slow-roll approximation and confirms ouranalytic results for double inflation.