Turning in the landscape: a new mechanism for generating Primordial Black Holes

TL;DR

This paper introduces a new, generic mechanism in multi-field inflation models where a sharp turn in the inflationary trajectory amplifies primordial fluctuations, leading to primordial black hole formation that could account for dark matter.

Contribution

It presents a novel, model-independent mechanism linking inflationary trajectory turns to primordial black hole production, applicable across multi-dimensional inflationary landscapes.

Findings

Amplification of primordial fluctuations occurs during strong turns in inflationary trajectory.

The duration and strength of the turn influence the black hole abundance.

Potential observational signatures include black hole spectrum and gravitational waves.

Abstract

We propose a new model-independent mechanism for producing primordial black holes from a period of multi-field inflation. This requires an enhancement of primordial fluctuations at short scales compared to their value at CMB scales. We show that such an amplification naturally occurs when the inflationary trajectory exhibits a strong turn, that is a limited period during which the trajectory strongly deviates from a geodesic in field space, and is sufficient for subsequently producing primordial black holes with the abundance to be all or a fraction of dark matter. Our mechanism is generic to models of inflation realized in a multi-dimensional field space with an overlying potential and geometry, also referred to as the inflationary landscape, as arises in embeddings of inflation in high-energy theories. We study analytically and numerically how the duration and the strength of the turn impact the primordial fluctuation power spectrum and the abundance of primordial black holes. Our mechanism has the potential of exhibiting unique features accessible to observation through the primordial black hole spectrum and the stochastic background of gravitational waves, offering a precious glimpse at the dynamics of inflation.