Dark matter signals on a laser interferometer

WIMPs are promising dark matter candidates. A WIMP occasionally collides with a mirror equipped with interferometric gravitational wave detectors such as LIGO, Virgo, KAGRA and the Einstein Telescope (ET). When WIMPs collide with a mirror of an interferometer, we expect that characteristic motions of the pendulum and mirror are excited, and those signals could be extracted by highly sophisticated sensors developed for gravitational wave detection. We analyze the motions of the pendulum and mirror, and estimate the detectability of these motions. For the "Thin-ET" detector, the signal-to-noise ratio may be 1.7 (m/D_M100 GeV ) , where m_DM is the mass of a WIMP. We may set a more strict upper limit on the cross section between a WIMP and a nucleon than the limits obtained by other experiments so far when m_DM is approximately lower than 0.2 GeV. We find an order-of-magnitude improvement in the upper limit around m_DM=0.2 GeV .