Primordial black hole formation for an anisotropic perfect fluid: Initial conditions and estimation of the threshold

Understand

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 in 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.