Sterile neutrino dark matter and low scale leptogenesis from a charged scalar

We show that novel paths to dark matter generation and baryogenesis are open when the standard model is extended with three sterile neutrinos Ni and a charged scalar delta(+). Specifically, we propose a new production mechanism for the dark matter particle-a multi-keV sterile neutrino, N-1 - that does not depend on the active-sterile mixing angle and does not rely on a large primordial lepton asymmetry. Instead, N-1 is produced, via freeze-in, by the decays of delta(+) while it is in equilibrium in the early Universe. In addition, we demonstrate that, thanks to the couplings between the heavier sterile neutrinos N-2,N-3 and delta(+), baryogenesis via leptogenesis can be realized close to the electroweak scale. The lepton asymmetry is generated either by N-2,N-3-decays for masses M-2,M-3 greater than or similar to TeV, or by N-2,N-3-oscillations for M-2,M-3 similar to GeV. Experimental signatures of this scenario include an X-ray line from dark matter decays, and the direct production of delta(+) at the LHC. This model thus describes a minimal, testable scenario for neutrino masses, the baryon asymmetry, and dark matter.