Hybrid seesaw from $SU(2{)}_1\times SU(2{)}_2\times U(1{)}_Y$

Abstract

We study neutrino mass generation in a model based on the $SU(3{)}_c\times SU(2{)}_1\times SU(2{)}_2\times U(1{)}_Y$ gauge symmetry, in which the Standard Model $SU(2{)}_L$ arises at low energies as the diagonal subgroup of the two $SU(2)$ factors. The symmetry is enlarged with a global $U(1{)}_{B-L}$ symmetry, spontaneously broken by the vacuum expectation value of a scalar bidoublet. Light neutrino masses are generated at tree level through a hybrid of the type-III, inverse and linear seesaw mechanisms. A distinctive feature of the construction is the existence of a Nambu-Goldstone boson, the majoron, which transforms non-trivially under the original gauge symmetry while being mostly singlet under the Standard Model gauge group. We explore the phenomenological consequences of this setup, including electroweak precision constraints, the production of the nearly degenerate $W^{\prime }$ and $Z^{\prime }$ bosons at colliders and lepton flavor violating decays with a majoron in the final state. The latter constitute the most promising signature of the model.

arXiv comment41 pages, 5 figures