Cosmic Microwave Background Observables of Small Field Models of Inflation

TL;DR

This paper introduces a new class of small field inflation models capable of predicting observable gravitational waves and negative spectral index running, aligning with recent cosmic microwave background data.

Contribution

It presents a novel class of small field inflation models that can produce observable gravitational waves and negative spectral index running, expanding the landscape of viable inflationary theories.

Findings

Models predict observable gravitational wave signals.

Models can produce negative spectral index running.

Models show higher power at smaller scales.

Abstract

We construct a class of single small field models of inflation that can predict, contrary to popular wisdom, an observable gravitational wave signal in the cosmic microwave background anisotropies. The spectral index, its running, the tensor to scalar ratio and the number of e-folds can cover all the parameter space currently allowed by cosmological observations. A unique feature of models in this class is their ability to predict a negative spectral index running in accordance with recent cosmic microwave background observations. We discuss the new class of models from an effective field theory perspective and show that if the dimensionless trilinear coupling is small, as required for consistency, then the observed spectral index running implies a high scale of inflation and hence an observable gravitational wave signal. All the models share a distinct prediction of higher power at smaller scales, making them easy targets for detection.