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

TL;DR

This paper explores a two-triplet type II seesaw model, revealing that the heavier doubly-charged scalar can predominantly decay into a singly-charged scalar and a W boson, impacting collider search strategies.

Contribution

It introduces a two-triplet model with mixing effects, showing novel decay channels for doubly-charged scalars not present in single-triplet scenarios.

Findings

The heavier doubly-charged scalar can decay into a singly-charged scalar and a W boson with over 99% branching ratio.

The model aligns with observed neutrino masses and mixings across various benchmark points.

Implications for LHC searches are discussed, highlighting new decay signatures.

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.