Non-Gaussianity and finite length inflation

TL;DR

This paper investigates how certain finite length inflation models with higher derivative interactions can produce large non-Gaussianity, especially in the flattened configuration, with the nonlinearity parameter strongly depending on the inflation duration.

Contribution

It demonstrates that finite length inflation models with specific interactions can generate large non-Gaussianity, linking inflation length to observable non-Gaussian signals.

Findings

Large non-Gaussianity (f_NL > 100) can occur for 60-63 e-folds of inflation.

Non-Gaussianity depends strongly on the length of inflation.

Models relate to CMB power spectrum suppression at low multipoles.

Abstract

In the present paper, certain inflation models are shown to have large non-Gaussianity in special cases. Namely, finite length inflation models with an effective higher derivative interaction, in which slow-roll inflation is adopted as inflation and a scalar-matter-dominated period or power inflation is adopted as pre-inflation, are considered. Using Holman and Tolley's formula of the nonlinearity parameter $f^\textrm{\tiny flattened}_\textrm{\tiny NL}$, we calculate the value of $f^\textrm{\tiny flattened}_\textrm{\tiny NL}$. A large value of $f^\textrm{\tiny flattened}_\textrm{\tiny NL}(f^\textrm{\tiny flattened}_\textrm{\tiny NL} > 100)$ can be obtained for all of the models considered herein when the length of inflation is 60-63 $e$-folds and $f_\textrm{\tiny NL}$ has strong dependence on the length of inflation. Interestingly, this length is similar to that for the case in which the suppression of the CMB angular power spectrum of $l=2$ was derived using the inflation models described in our previous papers.