Large non-Gaussianity from multi-brid inflation

TL;DR

This paper explores multi-brid inflation models with exponential potentials, demonstrating that large non-Gaussianity can occur even with equal masses and that both non-Gaussianity and tensor-to-scalar ratio can be detectable.

Contribution

It generalizes previous multi-brid inflation models by considering exponential potentials and more general end-of-inflation conditions, showing large non-Gaussianity is achievable in broader scenarios.

Findings

Large non-Gaussianity possible with equal-mass models.

Models with detectable non-Gaussianity and tensor-to-scalar ratio identified.

Generalized end-of-inflation conditions expand model viability.

Abstract

A model of multi-component hybrid inflation, dubbed multi-brid inflation, in which various observable quantities including the non-Gaussianity parameter f_{NL} can be analytically calculated was proposed recently. In particular, for a two-brid inflation model with an exponential potential and the condition that the end of inflation is an ellipse in the field space, it was found that, while keeping the other observational quantities within the range consistent with observations, large non-Gaussianity is possible for certain inflationary trajectories, provided that the ratio of the two masses is large. One might question whether the resulting large non-Gaussianity is specific to this particular form of the potential and the condition for the end of inflation. In this paper, we consider a model of multi-brid inflation with a potential given by an exponential function of terms quadratic in the scalar field components. We also consider a more general class of ellipses for the end of inflation than those studied previously. Then, focusing on the case of two-brid inflation, we find that large non-Gaussianity is possible in the present model even for the equal-mass case. Then by tuning the model parameters, we find that there exist models for which both the non-Gaussianity and the tensor-to-scalar ratio are large enough to be detected in the very near future.