Scalar-mediated dark matter model at colliders and gravitational wave
  detectors -- A White paper for Snowmass 2021
  The weakly interacting massive particles (WIMPs) have been the most popular
particle dark matter (DM) candidate for the last several decades, and it is
well known that WIMP can be probed via the direct, indirect and collider
experiments. However, the direct and indirect signals are highly suppressed in
some scalar-mediated DM models, e.g. the lepton portal model with a Majorana DM
candidate. As a result, collider searches are considered as the only hope to
probe such models. In this white paper, we propose that the gravitational wave
(GW) astronomy also serves as a powerful tool to probe such scalar mediated
WIMP models via the potential first-order phase transition GW signals. An
example for the lepton portal dark matter is provided, showing the
complementarity between collider and GW probes.
