Primordial black holes from a curvaton: the role of bimodal distributions

We investigate the formation of primordial black holes in curvaton models of inflation, where the curvature perturbation is not only generated by the inflaton but also by a light scalar field (the curvaton) that decays after inflation. During inflation, both fields are subject to quantum diffusion, owing to small-scale vacuum fluctuations crossing out the Hubble radius. After inflation, whether the curvaton dominates the universe or not depends on its field value when inflation ends. Since that value is stochastic, different regions of the universe undergo different post-inflationary histories. In practice, we show that this results in a double-peaked distribution for the number of e-folds realised in these models. Since that number of e-folds is related to the curvature perturbation by the δN formalism, the presence of a second peak has important consequences for primordial black holes that we discuss.