Inflation: perturbation theory and beyond.

Inflationary perturbations are approximately Gaussian and deviations from Gaussianity are the subject of an intense theoretical and experimental study. Deviations from Gaussianity are usually calculated using perturbation theory. This method, however, fails for unlikely events on the tail of the probability distribution, like the formation of a primordial black hole. I will explain how one can explore these unlikely tails using semiclassical methods.