We use microscopic many-body theory to analyze the problem of itinerant
ferromagnetism in a repulsive atomic Fermi gas of Hard Spheres. Using simple
arguments, we show that the available theoretical predictions for the onset of
the ferromagnetic transition predict a transition point at a density (kFa∼1) that is too large to be compatible with the universal low-density
expansion of the energy. We present new variational calculations for the
hard-sphere Fermi gas, in the framework of Fermi hypperneted chain theory, that
shift the transition to higher densities (kFa∼1.8). Backflow
correlations, which are mainly active in the unpolarized system, are essential
for this shift