Speaker
Description
We have investigated primordial black holes formation within a model of the early Universe dominated by a massless scalar field, developing a numerical spherically symmetric code dedicated to this problem. Imposing initial conditions on super horizon scales using the gradient expansion approach, we show that a massless scalar filed is equivalent to a perfect fluid, where the pressure is equal to the total energy density, only in the regime of cosmological expansion, while during the gravitational collapse space-like gradients arises and the comoving slicing is failing. For this reason, moving to a constant mean curvature slicing, we follow entirely the numerical evolution of cosmological perturbations, also during the gravitational collapse, computing the threshold $\delta_c$ for primordial black hole formation, and the corresponding mass distribution described by critical collapse.
