Single-field inflation, anomalous enhancement of superhorizon fluctuations and non-Gaussianity in primordial black hole formation

We show a textbook potential for single-field inflation, namely the Coleman-Weinberg model can induce double inflation and formation of primordial black holes (PBHs), because fluctuations that leave the horizon near the end of first inflation are anomalously enhanced at the onset of second inflation when the time-dependent mode turns into a growing mode rather than a decaying mode. The mass of PBHs produced in this mechanism with an appreciable density are distributed at certain intervals depending on the model parameters. We also calculate the effects of non-Gaussian statistics due to higher-order interactions on the abundance of PBHs, which turns out to be small.