The minimal SU(5) theory augmented by the fermionic adjoint representation restores the coupling constant unification and gives realistic neutrino masses and mixing through the hybrid Type I and Type III seesaw. The crucial prediction of the theory is an SU(2) lepton triplet with the mass below TeV. We study the signature of these heavy leptons at the hadron and lepton colliders. The smoking gun evidence of the theory, as in general seesaw mechanisms, is $\Delta L=2$ lepton-number violation through events of a pair of like-sign leptons plus four jets without significant missing energy at hadron colliders. We find that via this unique channel the heavy lepton can be searched for up to a mass of 200 GeV at the Tevatron with $8{\mathrm{fb}}^{-1}$, and up to 450 (700) GeV at the LHC of 14 TeV C.M. energy with $10(100){\mathrm{fb}}^{-1}$. The 7 TeV LHC run of $1{\mathrm{fb}}^{-1}$ is expected to probe a mass window of 110–200 GeV. We also comment on how to distinguish this theory from other models with similar heavy leptons. Finally, we compare the production rates and angular distributions of heavy leptons in $e^{+}{e}^{-}$ collisions for various models.

• Received 29 May 2009

DOI:https://doi.org/10.1103/PhysRevD.82.053004