Neutrino masses, leptogenesis and dark matter in hybrid seesaw

TL;DR

This paper proposes a hybrid seesaw model where certain right-handed neutrinos do not contribute to neutrino masses, enabling strong couplings, Higgs decays to neutrinos, and providing a dark matter candidate, while explaining neutrino masses and baryon asymmetry.

Contribution

It introduces a novel hybrid seesaw framework with a symmetry that decouples some right-handed neutrinos from neutrino mass generation, linking neutrino masses, dark matter, and leptogenesis.

Findings

Right-handed neutrinos can have strong Yukawa couplings without affecting neutrino masses.

The Higgs boson can decay predominantly into a left and a right-handed neutrino.

A stable right-handed neutrino serves as a cold dark matter candidate.

Abstract

We suggest a hybrid seesaw model where relatively ``light''right-handed neutrinos give no contribution to the neutrino mass matrix due to a special symmetry. This allows their Yukawa couplings to the standard model particles to be relatively strong, so that the standard model Higgs boson can decay dominantly to a left and a right-handed neutrino, leaving another stable right-handed neutrino as cold dark matter. In our model neutrino masses arise via the type-II seesaw mechanism, the Higgs triplet scalars being also responsible for the generation of the matter-antimatter asymmetry via the leptogenesis mechanism.