Right-handed dark matter from Higgs portal induced mixing

Abstract

Right-handed (RH) Higgs-induced neutrino mixing (RHINO) is an extremely exciting model that is capable of accounting for not only dark matter (DM), but also neutrino masses through the type-1 seesaw model along with the matter-antimatter asymmetry of the universe with leptogenesis. Within this model, the standard model is extended by not only introducing Majorana RH neutrino fields but also a five-dimensional Higgs portal-like effective operator, which is capable of producing and converting a source RH neutrino into a dark RH neutrino, which can play the role of DM. This operator harbours the potential to also induce decays of the dark RH neutrino, which could, in theory, be detected. This is extremely interesting as recently a neutrino flux excess at $\mathcal{O}(100\text{TeV})$ energies has been confirmed by the IceCube collaboration when analysing the 7.5yr HESE data, wherein the DM neutrino decays could contribute to this excess. The novel aspect of this work is the realisation that the five-dimensional operator could be expanded to allow production of the source RH neutrino, which in turn allows the particle to thermalise without requiring some external physics, thus allowing one to successfully account for the relic abundance whilst allowing a much higher seesaw scale. This higher scale can be above the sphaleron freeze-out temperature and can be as high as $\sim$100TeV, therefore allowing the incorporation of strong resonant leptogenesis within the model; thus, one can resolve the matter-antimatter asymmetry of the universe. Within our results, we obtain a $\sim$1TeV-1PeV allowed neutrino mass range for the dark RH neutrino. Additionally, our results indicate an effective scale for the Higgs portal interactions, which appears to be that of the hypothetical grand-unified scale $\sim10^{16}$ GeV, which is many orders of magnitude below the effective mixing scale $\sim10^{23}$GeV. Within this work, we also explain how this apparent hierarchy can arise from two UV-complete theories, where the first theory features a SM extension involving a heavy scalar as the mediator, whilst the second and more interesting extension involves a heavy fermion as the mediator, where we see that the first scale corresponds to the scale of new physics, whilst the second much smaller scale is related to very small couplings that can be identified with a symmetry breaking parameter. To summarise, the RHINO model allows us to simply unify neutrino masses, the matter-antimatter asymmetry of the universe, and DM in a testable manner, due to potential decays of the dark RH neutrino, which can be successfully embedded within a grand unified model.

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