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 initial conditions describing cosmological perturbations in super horizon regime, using covariant form equation state terms pressure and energy density gradients. The effect anisotropy is to modify shape respect isotropic case. Using dependence threshold $\delta_\mathrm{c}$ for perturbations, we estimate here how varying amplitude anisotropy. If this variation large enough it could lead significant abundance PBHs.