  The effect of polydispersity on the freezing transition of hard spheres is
examined within a moment description. At low polydispersities a single
fluid-to-crystal transition is recovered. With increasing polydispersity we
find a density above which the crystal melts back into an amorphous phase. The
range of densities over which the crystalline phase is stable shrinks with
increasing polydispersity until, at a certain level of polydispersity, the
crystal disappears completely from the equilibrium phase diagram. The two
transitions converge to a single point which we identify as the polydisperse
analogue of a point of equal concentration. At this point, the freezing
transition is continuous in a thermodynamic sense.
