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

Abstract

We show that novel paths to dark matter generation and baryogenesis are open when the standard model is extended with three sterile neutrinos Niand a charged scalar δ+. Specifically, we propose a new production mechanism for the dark matter particle—a multi-keV sterile neutrino,N1—that does not depend on the active-sterile mixing angle and does not rely on a large primordial lepton asymmetry. Instead,N1 is produced, via freeze-in, by the decays ofδ+ while it is in equilibrium in the early Universe. In addition, we demonstrate that, thanks to the couplings between the heavier sterile neutrinos N2,3 andδ+, baryogenesis via leptogenesis can be realized close to the electroweak scale. The lepton asymmetry is generated either by N2,3-decays for masses M2,3≳TeV, or by N2,3-oscillations for M2,3∼ GeV. Experimental signatures of this scenario include an X-ray line from dark matter decays, and the direct production ofδ+ at the LHC. This model thus describes a minimal, testable scenario for neutrino masses, the baryon asymmetry, and dark matter.