Two Higgs doublet type III seesaw with μ-τ symmetry at LHC

Abstract

We propose a two Higgs doublet Type III seesaw model with μ-τ flavor symmetry. We add an additional SU(2) Higgs doublet and three SU(2) fermion triplets in our model. The presence of two Higgs doublets allows for an explanation of small neutrino masses with triplet fermions in the 100 GeV mass range, without reducing the Yukawa couplings to extremely small values. The triplet fermions couple to the gauge bosons and can be thus produced at the LHC. We study in detail the effective cross-sections for the production and subsequent decays of these heavy exotic fermions. We show for the first time that the μ-τ flavor symmetry in the low energy neutrino mass matrix results in mixing matrices for the neutral and charged heavy fermions that are not unity and which carry the flavor symmetry pattern. This flavor structure can be observed in the decays of the heavy fermions at LHC. The large Yukawa couplings in our model result in the decay of the heavy fermions into lighter leptons and Higgs with a decay rate which is about 1011 times larger than what is expected for the one Higgs Type III seesaw model with 100 GeV triplet fermions. The smallness of neutrino masses constrains the neutral Higgs mixing angle sin α in our model in such a way that the heavy fermions decay into the lighter neutral CP even Higgs h0, CP odd Higgs A0 and the charged Higgs H±, but almost never to the heavier neutral CP even Higgs H0. The small value for sin α also results in a very long lifetime for h0. This displaced decay vertex should be visible at LHC. We provide an exhaustive list of collider signature channels for our model and identify those that have very large effective cross-sections at LHC and almost no standard model background.