We discuss features of the inflaton potential that can lead to a strong enhancement of the power spectrum of curvature perturbations. We show that a steep decrease of the potential induces an enhancement of the spectrum by several orders of magnitude, which may lead to the production of primordial black holes. The same feature can also create a distinctive oscillatory pattern in the spectrum of gravitational waves generated through the scalar perturbations at second order. We study the additive effect of several such features. We analyse a simplified potential, but also discuss the possible application to supergravity models.
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