  The formation of primordial black holes in the early universe may happen
through the collapse of large curvature perturbations generated during a
non-attractor phase of inflation or through a curvaton-like dynamics after
inflation. The fact that such small-scale curvature perturbation is typically
non-Gaussian leads to the renormalization of composite operators built up from
the smoothed density contrast and entering in the calculation of the primordial
black abundance. Such renormalization causes the phenomenon of operator mixing
and the appearance of an infinite tower of local, non-local and
higher-derivative operators as well as to a sizable shift in the threshold for
primordial black hole formation. This hints that the calculation of the
primordial black hole abundance is more involved than what generally assumed.
