Bispectra from two-field inflation using the long-wavelength formalism

Abstract

We use the long-wavelength formalism to compute the bispectral non-Gaussianity produced in two-field inflation. We find an exact result that is used as the basis of numerical studies, and an explicit analytical slow-roll expression for several classes of potentials that gives insight into the origin and importance of the various contributions to fNL. We also discuss the momentum dependence of fNL. Based on these results we find a simple model that produces a relatively large non-Gaussianity. We show that the long-wavelength formalism is a viable alternative to the standard delta-N formalism, and can be preferable to it in certain situations.

v3: Final version. Minor textual changes

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• Planck 2013 Results. XXIV. Constraints on primordial non-Gaussianity
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• Isocurvature modes in the CMB bispectrum
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• Isocurvature modes: joint analysis of the CMB power spectrum and bispectrum