GeV Seesaw, Accidentally Small Neutrino Masses, and Higgs Decays to Neutrinos

Understand

If the Standard Model particle content is extended by gauge singlet fermions (right-handed neutrinos), active neutrinos generically acquire (Majorana) masses, in agreement with our current understanding of the lepton sector.

• If the right-handed neutrino masses are of the same order as the electroweak symmetry breaking scale, it is usually expected that these will not mediate any experimentally observable effects.
• Here, I explore the fact that this is not necessarily the case.
• If neutrino masses are "accidentally small", active-sterile mixing angles can, according to current experimental bounds, be as large as several percent.