The sinusoidal valley: a recipe for high peaks in the scalar and induced tensor spectra

TL;DR

This paper introduces a sinusoidal interaction in multi-field inflation models that causes multiple turns in field space, significantly amplifying the power spectrum at certain scales and enabling phenomena like primordial black holes and gravitational waves.

Contribution

It presents a novel mechanism using a sine-type interaction to generate large peaks in the scalar and tensor spectra during inflation, applicable both as a standalone feature and as an add-on to existing models.

Findings

Enhanced power spectrum at specific scales by several orders of magnitude

Potential to produce primordial black holes and gravitational waves

Mechanism remains effective in more complex inflationary models

Abstract

Adding a sine-type interaction to inflationary models with two fields can evoke a classical trajectory with many turns in field space. Under conditions we discuss, the enhancement of the spectrum of adiabatic fluctuations resulting from each turn adds up. A special range of scales away from the CMB-constrained region can then be enhanced by several orders of magnitude, allowing for interesting phenomenological possibilities, such as induced gravitational waves or primordial black holes. A localized version of this interaction can also be used as an add-on to conventional inflationary models, thus allowing the injection of the large peak in their power spectra. The intuition and the conclusions drawn from this simple model remain relevant for more complicated applications that usually include extra terms that obscure the simplicity of the mechanism.