Freeze-in Leptogenesis via Dark Matter Oscillations

"Models of freeze-in dark matter that incorporate two or more dark matter mass eigenstates, typically below approximately 100 keV, can simultaneously account for the observed baryon asymmetry through the oscillations of the out-of-equilibrium dark matter particles. We consider the case in which the dark matter is produced by early-universe decays of electroweak-charged scalars, the lightest of which is typically in the few hundred GeV to few TeV range to realize the observed dark matter and baryon densities. Using a network of quantum kinetic equations that describe dark matter production, annihilation, and oscillations, along with Standard Model processes, we find that the minimal model, with two dark matter mass eigenstates and a single scalar, is tightly constrained once we take into account astronomical bounds on warm dark matter. Including Yukawa couplings of the scalar beyond its interaction with the dark matter or adding one or more additional scalars significantly expands the viable parameter space, much of which has the lightest scalar being long-lived at the Large Hadron Collider."