Decay Rates of Heavy Neutrinos in the Grimus–Neufeld Model

In this work, we take the Grimus–Neufeld model, which extends the Standard Model by adding a sterile neutrino and a second Higgs doublet. We calculate the decay rates for the heaviest neutrino, and by that the life-time, in the tiny seesaw scenario. The tree-level decay is mediated by the \(Z\) boson and the neutral Higgs bosons. The loop-level decay into a neutrino and a photon can dominate in some parameter regions. Abstract Published by the Jagiellonian University 2026 authors