Abstract
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.
Highlights
The minimal model addressing these three issues requires one sterile neutrino N1 at the keV scale as dark matter candidate [1], and two additional sterile neutrinos N2,3 for leptogenesis, which is induced either by N -decays, for sterile neutrino masses above the TeV scale [2], or by N -oscillations, for sterile neutrino masses at the GeV scale [3,4]
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 δ+
One may argue that no new physics is needed above the electroweak scale to explain neutrino masses, baryogenesis, and dark matter, defining the so-called “ν minimal standard model” [5]
Summary
The minimal model addressing these three issues requires one sterile neutrino N1 at the keV scale as dark matter candidate [1], and two additional sterile neutrinos N2,3 for leptogenesis, which is induced either by N -decays, for sterile neutrino masses above the TeV scale [2], or by N -oscillations, for sterile neutrino masses at the GeV scale [3,4]. One may argue that no new physics is needed above the electroweak scale to explain neutrino masses, baryogenesis, and dark matter, defining the so-called “ν minimal standard model” (νMSM) [5]. Such a model is undoubtedly economical and very predictive, by reason of the small number of degrees of freedom it contains, but it is strongly constrained. Leptogenesis via N2,3-oscillations within the νMSM requires a significant tuning of parameters, in particular a strong mass degeneracy between N2 and N3 [6] It is important, to consider alternative ways of realizing leptogenesis and producing sterile neutrinos within extensions of the νMSM.
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