Threshold of Primordial Black Hole Formation in Nonspherical Collapse
  We perform (3+1)-dimensional simulations of primordial black hole (PBH)
formation starting from the spheroidal super-horizon perturbations. We
investigate how the ellipticity (prolateness or oblateness) affects the
threshold of PBH formation in terms of the peak amplitude of curvature
perturbation. We find that, in the case of the radiation-dominated universe,
the effect of ellipticity on the threshold is negligibly small for large
amplitude of perturbations expected for PBH formation.
