  I discuss the dynamical interaction of galactic disks with the surrounding
dark matter halos. In particular it is demonstrated 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 counterparts of the
perturbations of the disk in the dark halo.

Astrophysics