Comments on non-Gaussian density perturbations and the production of   primordial black holes
  We review the basic arguments for the likelihood of non-Gaussian density perturbations in inflation models with primordial black hole (PBH) production. We discuss our derived distributions of field fluctuations and their implications, specifically commenting on the fine-tuning problem. We also discuss how the derived distributions may be affected when linked to metric perturbations. While linking the metric perturbations to field fluctuations in a nonlinear way may be important for determining exact probability distributions, the correct mapping is not self-evident. The calculation of P. Ivanov, which yields skew positive distribution, is based on an ansatz for the behavior of the nonlinear metric perturbation. We note that the ``natural'' generalization of the gauge-invariant formalism favored by Bond and Salopek yields an effective linear link between the distribution of field fluctuations and metric perturbations during inflation. 
James S. Bullock, Joel R. Primack (Physics Department, UCSC)