The arxiv article covers that. If the neutrinos are majorana then they are their own antiparticle so they don't interact with Higgs field. And with the lighte

The arxiv article covers that. If the neutrinos are majorana then they are their own antiparticle so they don't interact with Higgs field. And with the lightest left handed neutrino massless then through the "seesaw mechanism" you can wind up with an exceptionally heavy right handed majorana neutrino, and by cosmology the mass needs to be around 4.8×10^8 GeV.