We study signatures of macroscopic dark matter (DM) in current and future
gravitational wave (GW) experiments. Transiting DM with a mass of
∼105−1015 kg that saturates the local DM density can be potentially
detectable by GW detectors, depending on the baseline of the detector and the
strength of the force mediating the interaction. In the context of laser
interferometers, we derive the gauge invariant observable due to a transiting
DM, including the Shapiro effect, and adequately account for the finite photon
travel time within an interferometer arm. In particular, we find that the
Shapiro effect can be dominant for short-baseline interferometers such as
Holometer and GQuEST. We also find that proposed experiments such as Cosmic
Explorer and Einstein Telescope can constrain a fifth force between DM and
baryons, at the level of strength ∼103 times stronger than gravity for,
e.g., kg mass DM with a fifth-force range of 106 m.Comment: 40 pages, 6 figure