The Robustness of n_s < 0.95 in Racetrack Inflation

TL;DR

This paper analyzes why racetrack inflation models typically predict a spectral index below 0.95, providing an analytic explanation and discussing conditions for higher spectral index values.

Contribution

It offers an analytic derivation of the spectral index in racetrack inflation and explores conditions for achieving higher values, highlighting the need for fine-tuning.

Findings

Spectral index n_s < 0.95 is common in racetrack inflation.

Analytic expression for n_s derived from simplified single-field model.

Higher n_s values require fine-tuning of the potential.

Abstract

A spectral index n_s < 0.95 appears to be a generic prediction of racetrack inflation models. Reducing a general racetrack model to a single-field inflation model with a simple potential, we obtain an analytic expression for the spectral index, which explains this result. By considering the limits of validity of the derivation, possible ways to achieve higher values of the spectral index are described, although these require further fine-tuning of the potential.