Non-Gaussianity from Inflation

TL;DR

The paper addresses whether inflation with extra light scalar fields can produce detectable non-Gaussianity through correlated adiabatic and isocurvature perturbations. It analyzes the CMB angular bispectrum in a mixed perturbation scenario, showing how non-Gaussian features generated in the extra scalar sector can be efficiently transferred to the inflaton via oscillations, yielding cross-term contributions to the bispectrum. It finds that sizeable non-Gaussianity can appear in both adiabatic and isocurvature modes, with a bispectrum that includes adiabatic, isocurvature, and cross components; in a cubic self-interaction model the non-Gaussian amplitude scales as f_NL ~ O(mu/H). This work provides a concrete observable signature for multi-field inflation, offering a pathway to detect or constrain such non-Gaussianity with future CMB experiments and to break degeneracies in cosmological parameters.

Abstract

Correlated adiabatic and isocurvature perturbation modes are produced during inflation through an oscillation mechanism when extra scalar degrees of freedom other than the inflaton field are present. We show that this correlation generically leads to sizeable non-Gaussian features both in the adiabatic and isocurvature perturbations. The non-Gaussianity is first generated by large non-linearities in some scalar sector and then efficiently transferred to the inflaton sector by the oscillation process. We compute the cosmic microwave background angular bispectrum, providing a characteristic feature of such inflationary non-Gaussianity,which might be detected by upcoming satellite experiments.