A frame independent classification of single field inflationary models

TL;DR

This paper introduces a frame-independent formalism for classifying single field inflationary models, revealing redundancies and enabling a unified understanding of models with identical observable predictions.

Contribution

It proposes a novel invariant formalism to categorize inflationary models, simplifying the comparison and identification of models with similar phenomenology.

Findings

Invariant formalism clarifies model redundancies

Recipe for recasting models in invariant terms

Facilitates classification of inflationary models

Abstract

Seemingly unrelated models of inflation that originate from different physical setups yield, in some cases, identical predictions for the currently constrained inflationary observables. In order to classify the available models, we propose to express the slow-roll parameters and the relevant observables in terms of frame and reparametrisation invariant quantities. The adopted invariant formalism makes manifest the redundancy that afflicts the current description of inflation dynamics and offers a straightforward way to identify classes of models which yield identical phenomenology. In this Letter we offer a step-to-step recipe to recast every single field inflationary model in the proposed formalism, detailing also the procedure to compute inflationary observables in terms of frame and reparametrisation invariant quantities. We hope that our results become the cornerstone of a new categorisation of viable inflationary models and open the way to a deeper understanding of the inflation mechanism.