Turning in the landscape: A new mechanism for generating primordial black holes

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.(c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons .org /licenses /by /4 .0/). Funded by SCOAP3.

Automated summary

We propose a new mechanism for producing primordial black holes during a period of multi-field inflation. This mechanism requires an enhancement of primordial fluctuations at short scales compared to those at CMB scales. We show that this amplification naturally occurs when the inflationary trajectory deviates strongly from a geodesic in field space, and can subsequently produce enough primordial black holes to account for all or a fraction of dark matter. Our mechanism is applicable to inflation models in a multi-dimensional field space, as occurs in high-energy theories. We analytically and numerically study how the duration and strength of the trajectory deviation affect the primordial fluctuation power spectrum and the abundance of primordial black holes. Our mechanism offers valuable insights into the dynamics of inflation through observable features in the primordial black hole spectrum and the stochastic background of gravitational waves.