Numerical stochastic inflation constrained by frozen noise

Stochastic inflation can resolve strong inflationary perturbations, which seed primordial black holes. I present a fast and accurate way to compute these perturbations in typical hole producing single-field models, treating the short-wavelength Fourier modes beyond de Sitter approximation. The squeezing freezing of reduces problem one dimension, resulting new form stochastic equations, dubbed `constrained inflation,' be solved efficiently with semi-analytical techniques numerical importance sampling. In an example case, perturbation distribution is resolved seconds deep into its non-Gaussian tail, speed-up factor $10^9$ compared previous study. Along way, comment on role momentum constraint inflation.