Localized Steps toward ACT-Favored Inflation

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.