Double inflation via non-minimally coupled spectator

TL;DR

This paper demonstrates that a non-minimally coupled spectator field can induce double inflation, alter inflationary predictions, and make quadratic chaotic inflation viable, expanding the landscape of inflationary models.

Contribution

It introduces a novel mechanism where a non-minimally coupled spectator field drives a second inflationary phase, modifying observable predictions and enabling quadratic chaotic inflation to be consistent with data.

Findings

Spectator non-minimal coupling leads to a second inflationary phase.

Isocurvature fluctuations influence adiabatic perturbations and inflation predictions.

Quadratic chaotic inflation becomes viable with spectator non-minimal coupling.

Abstract

We argue that double inflation may occur when a spectator field is non-minimally coupled to gravity. As a concrete example, we study a two-field inflationary model where the initial spectator field is non-minimally coupled to gravity while the initial inflaton field is minimally coupled. The non-minimal coupling results in the growth of the spectator field which, in turn, drives the second stage of inflation in a significant region of parameter space. The isocurvature fluctuations originating from the spectator field source adiabatic ones, and hence the spectator non-minimal coupling can modify the inflationary predictions for the spectral index and the tensor-to-scalar ratio even though the initial inflaton field is minimally coupled to gravity. We explicitly show that quadratic chaotic inflation can become viable by the introduction of the spectator non-minimal coupling.