A simple mechanism for the enhancement of the inflationary power spectrum

TL;DR

This paper introduces a simple mechanism in two-field inflation models where sharp turns in the inflationary trajectory amplify fluctuations, creating peaks in the power spectrum that could lead to primordial black holes and gravitational waves.

Contribution

It presents an intuitive, easily implementable mechanism for enhancing the inflationary power spectrum through rapid turns in two-field models.

Findings

Sharp turns cause significant amplification of fluctuations.

Enhanced power spectrum peaks can produce primordial black holes.

Mechanism applicable in simple two-field inflation models.

Abstract

The background evolution in two-field inflation can feature two distinct stages, corresponding to the evolution along two successive field directions. When the second stage occurs at a significantly lower energy scale, the inflationary trajectory includes a sharp transition, accompanied by a series of rapid turns in field space. Fluctuations crossing the Hubble horizon during this turning phase can experience amplification by several orders of magnitude. This mechanism is very intuitive and can be implemented even in simple two-field models. It produces a peak in the scalar power spectrum that can lead to significant abundances of primordial black holes and secondary gravitational waves.