Multiple field ultraslow-roll inflation: Primordial black holes from straight bulk and distorted boundary
Sina Hooshangi, Alireza Talebian, Mohammad Hossein Namjoo, Hassan Firouzjahi
Abstract
We study a model of two-field ultraslow-roll (USR) inflation bounded by a curve in the field space. Curvature perturbations and non-Gaussianities can be enhanced both during the USR phase and from the inhomogeneities at the boundary. We employ the full nonlinear $\ensuremath{\delta}N$ formalism to calculate the probability distribution function (PDF) for curvature perturbation nonperturbatively and show that nonlinear effects can significantly enhance the abundance of primordial black holes (PBHs). For large curvature perturbations, the PDF has a universal exponential tail, but for the intermediate values, the PDF---and, therefore, the abundance of the PBHs---depend sensitively on the geometry of the boundary.