Three loop neutrino model with isolated k

We propose a three loop radiative neutrino mass scenario with an isolated doubly charged singlet scalar k[+ or -][+ or -] without couplings to the charged leptons, while two other singly charged scalars h1[+ or -] and h2[+ or -] attach to them. In this setup, the lepton flavor violation originating from k[+ or -][+ or -] exchanges is suppressed and the model is less constrained, where some couplings can take sizable values. The sizable couplings can help us to enhance neutrino masses without drastically large scalar trilinear couplings appearing in a neutrino mass matrix, which tends to drive the vacuum stability to become jeopardized at the one loop level. Note that the other h1[+ or -] and h2[+ or -] should be heavy at least around a few TeV. We suitably arrange the charges of an additional global U(1) symmetry, where the decay constant of the associated Nambu-Goldstone boson can be around a TeV scale consistently. Consistent solutions are found, but a part of them is now on the edge.