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 $$N_i$$ 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 $$N_{2,3}$$ and $$\delta ^+$$, baryogenesis via leptogenesis can be realized close to the electroweak scale. The lepton asymmetry is generated either by $$N_{2,3}$$-decays for masses $$M_{2,3}\gtrsim $$ TeV, or by $$N_{2,3}$$-oscillations for $$M_{2,3}\sim $$ 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