Non-gaussianities for primordial black hole formation
  We analyze primordial non-gaussianities in presence of an ultra-slow phase
during the inflationary dynamics, focusing on scenarios relevant for the
production of primordial black holes. We compute the three-point correlation
function of comoving curvature perturbations finding that non-gaussianities are
sizable, and predominantly local. In the context of threshold statistics, we
analyze their impact for the abundance of primordial black holes, and their
interplay with the non-gaussianities arising from the non-linear relation
between density and curvature perturbations. We find that non-gaussianities
significantly modify the estimate of the primordial black holes abundance
obtained with the gaussian approximation. However, we show that this effect can
be compensated by a small change, of a factor $2\div3$ at most, of the
amplitude of the primordial power spectrum of curvature perturbations. This is
obtained with a small tuning of the parameters of the inflationary model.
