Predictions for Nongaussianity from Nonlocal Inflation

TL;DR

This paper provides the first precise calculation of non-Gaussianity in nonlocal inflation models, demonstrating that the bispectrum can be significantly large and distinguishable from other inflationary models.

Contribution

It introduces a new method for exact computation of the bispectrum in nonlocal inflation, advancing understanding of non-Gaussian signatures in such models.

Findings

Large non-Gaussianity can be generated in nonlocal inflation.

The bispectrum shape is distinct from Dirac-Born-Infeld inflation.

Exact computation confirms previous estimates of significant non-Gaussianity.

Abstract

In our previous work the nonlinearity parameter f_NL, which characterizes nongaussianity in the cosmic microwave background, was estimated for a class of inflationary models based on nonlocal field theory. These models include p-adic inflation and generically have the remarkable property that slow roll inflation can proceed even with an extremely steep potential. Previous calculations found that large nongaussianity is possible; however, the technical complications associated with studying perturbations in theories with infinitely many derivatives forced us to provide only an order of magnitude estimate for f_NL. We reconsider the problem of computing f_NL in nonlocal inflation models, showing that a particular choice of field basis and recent progress in cosmological perturbation theory makes an exact computation possible. We provide the first quantitatively accurate computation of the bispectrum in nonlocal inflation, confirming our previous claim that it can be observably large. We show that the shape of the bispectrum in this class of models makes it observationally distinguishable from Dirac-Born-Infeld inflation models.