Primordial black hole formation for an anisotropic perfect fluid:
  initial conditions and estimation of the threshold
  This work investigates the formation of primordial black holes within a
radiation fluid with an anisotropic pressure. We focus our attention on the
initial conditions describing cosmological perturbations on the super horizon
regime, using a covariant form of the equation of state in terms of pressure
and energy density gradients. The effect of the anisotropy is to modify the
initial shape of the cosmological perturbations with respect to the isotropic
case. Using the dependence of the threshold $\delta_\mathrm{c}$ for primordial
black holes with respect to the shape of cosmological perturbations, we
estimate here how the threshold is varying with respect to the amplitude of the
anisotropy. If this is large enough this could lead to a significant variation
of the abundance of PBHs.
