  The ground state of a homogeneous Bose gas of hard spheres is treated in
self-consistent mean-field theory. It is shown that this approach provides an
accurate description of the ground state of a Bose-Einstein condensed gas for
arbitrarily strong interactions. The results are in good agreement with Monte
Carlo numerical calculations. Since all other mean-field approximations are
valid only for very small gas parameters, the present self-consistent theory is
a unique mean-field approach allowing for an accurate description of Bose
systems at arbitrary values of the gas parameter.
