Running Spectral Index from Inflation with Modulations

TL;DR

This paper proposes that periodic modulations in the inflaton potential can explain a large negative running spectral index suggested by CMB data, predicting enhanced small-scale perturbations detectable by future 21 cm observations.

Contribution

It introduces a model with superimposed oscillations in the inflaton potential to account for observed spectral index running, linking potential features to observable signatures.

Findings

Explains large negative running spectral index with modulated inflaton potential

Predicts enhanced small-scale perturbations due to potential oscillations

Suggests future 21 cm observations could detect these small-scale features

Abstract

We argue that a large negative running spectral index, if confirmed, might suggest that there are abundant structures in the inflaton potential, which result in a fairly large (both positive and negative) running of the spectral index at all scales. It is shown that the center value of the running spectral index suggested by the recent CMB data can be easily explained by an inflaton potential with superimposed periodic oscillations. In contrast to cases with constant running, the perturbation spectrum is enhanced at small scales, due to the repeated modulations. We mention that such features at small scales may be seen by 21 cm observations in the future.