Non-Gaussianities in the PBH Formation and Induced GWs

by Prof. Shi Pi (Institute of Theoretical Physics, Chinese Academy of Sciences)

Thursday 18 Jan 2024, 16:00 → 17:30 Asia/Seoul

Room 1423 (KIAS)

Title: Non-Gaussianities in the PBH Formation and Induced GWs

Speaker: Shi Pi (Institute of Theoretical Physics, Chinese Academy of Sciences)

Abstract: I will briefly review the recent progress in the non-Gaussian effect on the PBH formation and the induced GWs. On large scales, the curvature perturbation ζ is proportional to the inflaton perturbation δφ, while higher order corrections are suppressed by slow-roll parameters. But on small scales when ζ is enhanced, the deviation to the slow-roll attractor is significant, leading to large nonlinear terms. I will show how to derive the fully nonlinear relation of ζ(δφ) in a general way in single-field inflation, which is a sum of logarithms contributed by all the non-attractor stages. When only one non-attractor stage dominates, the PDF of ζ degenerates to the renowned "exponential tail”, or a double exponential suppression, depending on the shape of the potential. Such non-Gaussianities must be taken into account in the calculation of PBH abundance. I will also briefly discuss its impact on the induced GWs, and the implication on the recent pulsar timing array signals.