Very low scale Coleman-Weinberg inflation with non-minimal coupling

TL;DR

This paper explores small-field Coleman-Weinberg inflation models with non-minimal gravity coupling, demonstrating how they can satisfy cosmological constraints and achieve very low inflation scales through model modifications.

Contribution

It introduces a logarithmic non-minimal coupling to extend the viability of small-field CW inflation models and explores parameter spaces with extremely low inflation scales.

Findings

Viable parameter space with low inflation scales down to 10^{-4} GeV.

Inclusion of a linear potential term broadens model viability.

Models can satisfy cosmological constraints with various e-fold numbers.

Abstract

We study viable small-field Coleman-Weinberg (CW) inflation models with the help of non-minimal coupling to gravity. The simplest small-field CW inflation model (with a low-scale potential minimum) is incompatible with the cosmological constraint on the scalar spectral index. However, there are possibilities to make the model realistic. First, we revisit the CW inflation model supplemented with a linear potential term. We next consider the CW inflation model with a logarithmic non-minimal coupling and illustrate that the model can open a new viable parameter space that includes the model with a linear potential term. We also show parameter spaces where the Hubble scale during the inflation can be as small as $10^{-4} $ GeV, $1$ GeV, $10^4 $ GeV, and $10^8$ GeV for the number of $e$-folds of $40,~45,~50$, and $55$, respectively, with other cosmological constraints being satisfied.