Detailed Calculation of Primordial Black Hole Formation During
  First-Order Cosmological Phase Transitions
  We recently presented a new mechanism for primordial black hole formation
during a first-order phase transition in the early Universe, which relies on
the build-up of particles which are predominantly reflected from the advancing
bubble wall. In this companion paper we provide details of the supporting
numerical calculations. After describing the general mechanism, we discuss the
criteria that need to be satisfied for a black hole to form. We then set out
the Boltzmann equation that describes the evolution of the relevant phase space
distribution function, carefully describing our treatment of the Liouville
operator and the collision term. Finally, we show that black holes will form
for a wide range of parameters.
