Neutrino Masses in the Mirror Twin Higgs with Spontaneous ℤ_2 Breaking

We introduce a mirror twin Higgs model with spontaneous ℤ_2 symmetry breaking that ameliorates the constraints in twin Higgs cosmology and, at the same time, generates the Standard Model neutrino masses. The model features an SU(2) triplet with hypercharge 1 alongside its twin counterpart. Spontaneous breaking of both ℤ_2 and electroweak symmetry occurs in the scalar sector. The Standard Model neutrinos acquire small masses through the type-II seesaw mechanism. In contrast, their twin counterparts acquire large masses, effectively addressing the dark radiation problem in mirror twin Higgs scenarios. We study the impact of the model on the N_ eff. constraints, as well as on collider phenomenology.