Gravitational Waves in Cold Dark Matter
  We study the effects of cold dark matter on the propagation of gravitational
waves of astrophysical and primordial origin. We show that the dominant effect
of cold dark matter on gravitational waves from astrophysical sources is a
small frequency dependent modification of the propagation speed of
gravitational waves. However, the magnitude of the effect is too small to be
detected in the near future. We furthermore show that the spectrum of
primordial gravitational waves in principle contains detailed information about
the properties of dark matter. However, depending on the wavelength, the
effects are either suppressed because the dark matter is highly
non-relativistic or because it contributes a small fraction of the energy
density of the universe. As a consequence, the effects of cold dark matter on
primordial gravitational waves in practice also appear too small to be
detectable.
