  In this Letter, we propose a new possible connection between dark matter
relic density and baryon asymmetry of the universe. The portal between standard
model sector and dark matter not only controls the relic density and detections
of dark matter, but also allows the dark matter to trigger the first order
electroweak phase transition. We discuss systematically possible scalar dark
matter candidates, starting from a real singlet to arbitrary high
representations. We show that the simplest realization is provided by a
doublet, and that strong first-order electroweak phase transition implies a
lower bound on the dark matter direct detection rate. The mass of dark matter
lies between 45 and 80 GeV, allowing for an appreciable invisible decay width
of the Standard Model Higgs boson, which is constrained to be lighter than 130
GeV for the sake of the strong phase transition.
