Doubly charged scalar decays in a type II seesaw scenario with two Higgs triplets

Abstract: The type II seesaw mechanism for neutrino mass generation usually makes use of one complex scalar triplet. The collider signature of the doubly-charged scalar, the most striking feature of this scenario,consists mostly in decays into same-sign dileptons or same-sign $W$ boson pairs. However, certain scenarios of neutrino mass generation, such as those imposing texture zeros by a symmetry mechanism, require at least two triplets in order to be consistent with type-II the seesaw mechanism. We develop a model with two such complex triplets and show that, in such a case, mixing between the triplets can cause the heavier doubly-charged scalar mass eigenstate to decay into a singly-charged scalar and a $W$ boson of the same sign. Considering a large number of benchmark points with different orders of magnitude of the $\Delta L =2$ Yukawa couplings, chosen in agreement with the observed neutrino mass and mixing pattern, we demonstrate that $H^{++}_1 \rightarrow H^+_2 W^+$ can have more than 99% branching fraction in the cases where the vacuum expectation values of the triplets are small. The implications of this for the LHC are pointed out.