Probing the seesaw mechanism at CERN LHC

We have recently proposed a simple SU(5) theory with an adjoint fermionic multiplet on top of the usual minimal spectrum. This leads to the hybrid scenario of both type I and type III seesaw and it predicts the existence of the fermionic SU(2) triplet between 100 GeV and 1 TeV for a conventional grand unified theory scale of about 10¹⁶ GeV, with main decays into W (Z) and leptons, correlated through Dirac Yukawa couplings, and lifetimes shorter than about 10^-12sec. These decays are lepton number violating and they offer an exciting signature of ΔL=2 dilepton events together with 4 jets at future $pp$ (pp̄) colliders. Increasing the triplet mass endangers the proton stability and so the seesaw mechanism could be directly testable at LHC.