Unifying leptogenesis, dark matter and high-energy neutrinos with right-handed neutrino mixing via Higgs portal

Abstract

We revisit a model in which neutrino masses and mixing are described by a two right-handed (RH) neutrino seesaw scenario, implying a strictly hierarchical light neutrino spectrum. A third decoupled RH neutrino, $N_{\mathrm{DM}}$ with mass $M_{\mathrm{DM}}$, plays the role of cold dark matter (DM) and is produced by the mixing with a source RH neutrino, $N_{\mathrm{S}}$ with mass $M_{\mathrm{S}}$, induced by Higgs portal interactions. The same interactions are also responsible for $N_{\mathrm{DM}}$ decays. We discuss in detail the constraints coming from DM abundance and stability conditions, showing that in the hierarchical case ($M_{\mathrm{DM}}\gg M_{\mathrm{S}}$) there is an allowed window on $M_{\mathrm{DM}}$, which necessarily implies a contribution from DM decays to the high-energy neutrino flux recently detected by IceCube. We also show how the model can explain the matter-antimatter asymmetry of the Universe via leptogenesis in the quasi-degenerate limit. In this case, the DM mass should be within the range 300 GeV $\lesssim M_{\mathrm{S}}<M_{\mathrm{DM}}\lesssim$ 10 PeV. We discuss the specific properties of this high-energy neutrino flux and show the predicted event spectrum for two exemplary cases. Although DM decays, with a relatively hard spectrum, cannot account for all the IceCube high-energy data, we illustrate how this extra source of high-energy neutrinos could reasonably explain some potential features in the observed spectrum. In this way, this represents a unified scenario for leptogenesis and DM that could be tested during the next years with more high-energy neutrino events.

Comments: 48 pages, 10 figures, version for publication in JCAP: v3: corrected calculation of the abundance of the source right-handed neutrino for initial vanishing abundance (Eq. (75)): the upper bound on the DM mass gets more stringent but conclusion almost unchanged; see footnote on the cover page for more details