No-Go Theorem for Gauss-Bonnet Inflation without Inflaton Potential

TL;DR

This paper demonstrates a no-go theorem indicating that Gauss-Bonnet inflation models without an inflaton potential are fundamentally unstable due to gradient instabilities in tensor perturbations.

Contribution

The paper proves a no-go theorem showing the inherent instability of Gauss-Bonnet inflation without an inflaton potential, challenging previous models proposing such scenarios.

Findings

Gradient instability in tensor perturbations identified

No consistent Gauss-Bonnet inflation without potential

Theoretical proof of the no-go theorem

Abstract

Recently, an interesting inflationary scenario, named Gauss-Bonnet inflation, is proposed by Kanti et al.~\cite{Kanti:2015pda,Kanti:2015dra}. In the model, there is no inflaton potential but the inflaton couples to the Guass-Bonnet term. In the case of quadratic coupling, they find inflation occurs with graceful exit. The scenario is attractive because of the natural set-up. However, we show there exists the gradient instability in the tensor perturbations in this inflationary model. We further prove the no-go theorem for the Gauss-Bonnet inflation without an inflaton potential.