Strongly coupled inert scalar sector with radiative neutrino masses

Abstract

We explore the phenomenological consequences of a model with an extended scalar sector, incorporating strongly coupled inert Higgs doublets. The model introduces three Higgs doublets: one that interacts with the $SU(2)$ symmetry of the Standard Model, and two inert doublets belonging to a strongly interacting sector, embedded in the $SU(2)_2 \times SU(2)_1 \times U(1)_Y$ electroweak gauge symmetry. This symmetry structure is further supplemented by a spontaneously broken $\mathbb{Z}_2$ and a preserved $\mathbb{Z}_2'$ discrete symmetry. Our approach harnesses the exotic scalar fields emerging from this sector to implement mass-generation mechanisms. In particular, a one-loop seesaw mechanism accounts for the smallness of neutrino masses, while a universal seesaw mechanism naturally explains the hierarchy of charged fermion masses below the top quark mass. The model is shown to be consistent with current experimental constraints, including those from charged lepton flavor violation, electroweak precision observables, the Higgs diphoton decay rate, and the Higgs trilinear self-coupling. Notably, it also provides a viable interpretation of the 95~GeV diphoton excess, offering a distinctive signature of new physics beyond the Standard Model.