  A spin-wave approach of the zero temperature superfluid-insulator transition
for two-dimensional hard-core bosons in a random potential $\mu=\pm$ W is
developed. While at the classical level there is no intervening phase between
the Bose-condensed superfluid (SF) and the gapped disordered insulator, the
introduction of quantum fluctuations leads to a much richer physics. Upon
increasing the disorder strength W, the Bose-condensed fraction disappears
first, before the SF. Then a gapless Bose-glass phase emerges over a finite
region until the insulator appears. Furthermore, in the strongly disordered SF
regime, a mobility edge in the spin-wave excitation spectrum is found at a
finite frequency $\Omega_c$ decreasing with W, and presumably vanishing in the
Bose-glass phase.
