Localized Steps toward ACT-Favored Inflation

TL;DR

The paper proposes that a localized step in the inflaton potential can reconcile certain inflation models with ACT measurements favoring a higher scalar spectral index, by shifting the predicted n_s and r values.

Contribution

It introduces a mechanism involving a localized step in the inflaton potential to adjust inflation model predictions to match ACT observations.

Findings

A smooth, localized step can shift n_s and r predictions.

This mechanism moves monomial and plateau-like models toward ACT-favored values.

Natural inflation remains less affected by this shift.

Abstract

Recent ACT measurements favor a scalar spectral index n_s larger than the Planck value, posing a challenge to many single-field slow-roll inflation models. We show that a smooth, localized step in the inflaton potential can shift the predicted values of n_s and r by displacing the field value at which the CMB pivot scale exits the horizon. This mechanism can move monomial and, in particular, plateau-like attractor models toward the ACT-favored region, whereas the induced shift remains insufficient in natural inflation.