  It is shown that if the self-gravitating shearing sheet, a model of a patch
of a galactic disk, is embedded in a live dark halo, this has a strong effect
on the dynamics of density waves in the sheet. I describe how the density waves
and the halo interact via halo particles either on orbits in resonance with the
wave or on non-resonant orbits. Contrary to expectation the presence of the
halo leads to a very considerable enhancement of the amplitudes of the density
waves in the shearing sheet. This effect appears to be the equivalent of the
recently reported enhanced growth of bars in numerically simulated stellar
disks embedded in live dark halos. Finally I discuss the transfer of linear
momentum from a density wave in the sheet to the halo and show that it is
mediated only by halo particles on resonant orbits.
