The Simplest Models of Radiative Neutrino Mass: Excluding Simplified Zee Models and Beyond

Understand

The complexity of radiative neutrino-mass models can be judged by: (i) whether they require the imposition of ad hoc symmetries, (ii) the number of new multiplets they introduce, and (iii) the number of arbitrary parameters that appear.

• Adopting the view that the imposition of arbitrary new symmetries is the least appealing approach, the simplest models have two new multiplets and a minimal number of new parameters.
• With this in mind, we search for the simplest models of radiative neutrino mass.
• We are lead to two new models, containing a real scalar triplet and a charged scalar doublet (respectively), in addition to the charged singlet scalar considered by Zee [h^+\sim(1,1,2)].