Quasi-Single Field Inflation and Non-Gaussianities

TL;DR

This paper investigates quasi-single field inflation models where massive isocurvature modes influence density perturbations, producing distinctive non-Gaussian signatures such as large bispectra and trispectra with novel shapes.

Contribution

It introduces a simple quasi-single field inflation model with a turning inflaton trajectory, revealing new non-Gaussian shapes and large trispectra effects.

Findings

Large bispectra with novel shapes between local and equilateral types.

Trispectra can be significantly large, with tNL exceeding fNL squared.

Non-Gaussianities are notably affected by massive isocurvature modes.

Abstract

In quasi-single field inflation models, massive isocurvature modes, that are coupled to the inflaton and have mass of order the Hubble parameter, can have nontrivial impacts on density perturbations, especially non-Gaussianities. We study a simple example of quasi-single field inflation in terms of turning inflaton trajectory. Large bispectra with a one-parameter family of novel shapes arise, lying between the well-known local and equilateral shape. The trispectra can also be very large and its magnitude tNL can be much larger than fNL squared.