Universality classes of inflation

TL;DR

This paper classifies single-field slow-roll inflation models into two universality classes based on their scaling with the number of e-folds, providing universal predictions for key observables like the spectral index and tensor-to-scalar ratio.

Contribution

It demonstrates that all such inflation models fall into two universality classes characterized by a single parameter, with universal predictions for spectral index and tensor-to-scalar ratio.

Findings

Models are classified into two universality classes.

Universal expressions for spectral index and r are derived.

Predicted r values are either very small or near current observational limits.

Abstract

We investigate all single-field, slow-roll inflationary models whose slow-roll parameters scale as 1/N in the limit of a large number of e-folds N. We proof that all such models belong to two universality classes, characterised by a single parameter. One class contains small field models like hilltop inflation, while the other class consists of large field models like chaotic inflation. We give the leading expressions for the spectral index and tensor-to-scalar ratio r, which are universal for each class, plus subleading corrections for a number of models. This predicts r either to be unobservably small, r<0.01, or close to the present observational limit, r~0.07.