Completing RHINO

TL;DR

The RHINO model unifies neutrino mass generation and matter origin, showing how Higgs portal interactions can produce dark neutrinos that explain dark matter and neutrino flux anomalies, with implications for high-scale physics.

Contribution

This work introduces a comprehensive RHINO framework that links neutrino masses, dark matter production, and matter-antimatter asymmetry within a grand unified context.

Findings

Dark neutrinos can serve as decaying dark matter up to 100 TeV.

Enhanced dark neutrino production can occur via thermalisation before oscillations.

Decays of dark neutrinos may explain IceCube high-energy neutrino excess.

Abstract

The right-handed (RH) Higgs-induced neutrino mixing (RHINO) model explains neutrino masses and origin of matter in the universe within a unified picture. The mixing, effectively described by a dimension five operator, is responsible both for the production of dark neutrinos, converting a small fraction of seesaw neutrinos acting as source, and for their decays. We show that including the production of source neutrinos from Higgs portal interactions, their abundance can thermalise prior to the onset of source-dark neutrino oscillations, resulting into an enhanced production of dark neutrinos that thus can play the role of decaying dark matter (DM) for a much higher seesaw scale. This can be above the sphaleron freeze-out temperature and as high as $\sim 100\,{\rm TeV}$, so that strong thermal resonant leptogenesis for the generation of the matter-antimatter asymmetry is viable. We obtain a $\sim 1\,{\rm TeV}$--$1\,{\rm PeV}$ allowed dark neutrino mass range. Intriguingly, their decays can also explain a neutrino flux excess at ${\cal O}(100\,{\rm TeV})$ energies recently confirmed by the IceCube collaboration analysing 7.5yr HESE data. Our results also point to an effective scale for Higgs portal interactions nicely identifiable with the grandunified scale and many orders of magnitude below the effective scale for the mixing. We explain this hierarchy in a UV-complete model with a very heavy fermion as mediator: the first scale corresponds to the fundamental scale of new physics, while the second is much higher because of a very small coupling identifiable with a symmetry breaking parameter. Therefore, RHINO realises a simple unified model of neutrino masses and origin of matter in the universe currently under scrutiny at neutrino telescopes and potentially embeddable within a grandunified model.