Primordial Black Holes from Inflation with a Spectator Field

Speaker: Dario Lorenzoni (University of Manitoba)
Date/Time: Thursday 11 December 2025, 14:00
Room: A.2.25/27 - Atlas at MPP, Garching

Title: Primordial Black Holes from Inflation with a Spectator Field

Abstract:
How is the production of primordial black holes (PBHs) in single-field models of inflation impacted by the presence of additional fields?
Scalar fields are ubiquitous in theories of high-energy physics, suggesting they may "spectate" inflation. We consider the effect of a spectator field -- which provides a subdominant source of energy density -- on inflationary models featuring a phase of ultra-slow roll (USR) evolution. Despite the modest title, the spectator field can have a dramatic impact: it prevents the system from entering into USR, naively precluding the production of PBHs. However, we demonstrate in a model-independent way that the growth of perturbations is maintained (or enhanced) by the spectator, through the rich interplay of curvature and isocurvature perturbations.
Furthermore, we highlight a degeneracy between the fine-tuning of the PBH model and the parameters of the spectator, leading to an overall resilience of model predictions to parameter variations. This makes it easier for the underlying PBH model to accommodate both high-precision CMB constraints and production of PBHs as dark matter candidates.
This talk is based on [2504.13251] and [2512.xxxxx] with S. Geller, D. Kaiser, E. McDonough, Z. Ireland, and K. Wittmeier.