  While global cosmological and local galactic abundance of dark matter is well
established, its identity, physical size and composition remain a mystery. In
this paper, we analyze an important question of dark matter detectability
through its gravitational interaction, using current and next generation
gravitational-wave observatories to look for macroscopic (kilogram-scale or
larger) objects. Keeping the size of the dark matter objects to be smaller than
the physical dimensions of the detectors, and keeping their mass as free
parameters, we derive the expected event rates. For favorable choice of mass,
we find that dark matter interactions could be detected in space-based
detectors such as LISA at a rate of one per ten years. We then assume the
existence of an additional Yukawa force between dark matter and regular matter.
By choosing the range of the force to be comparable to the size of the
detectors, we derive the levels of sensitivity to such a new force, which
exceeds the sensitivity of other probes in a wide range of parameters. For
sufficiently large Yukawa coupling strength, the rate of dark matter events can
then exceed 10 per year for both ground- and space-based detectors. Thus,
gravitational-wave observatories can make an important contribution to a global
effort of searching for non-gravitational interactions of dark matter.
