Testing the realistic seesaw model with two heavy Majorana neutrinos at the CERN Large Hadron Collider

In the conventional type-(I + II) seesaw model, the effective mass matrix of three known light neutrinos is given by Mν=ML−MDMR−1MDT in the leading-order approximation. We propose an intriguing scenario, in which the structural cancellation condition MDMR−1MDT=0 is guaranteed by the A4×Z2A4×Z2 flavor symmetry. As a consequence, neutrino masses are mainly generated by the Higgs triplet Mν=MLMν=ML, while the neutrino mixing matrix is non-unitary and takes on the nearly tri-bimaximal pattern. A discriminating feature of this scenario from the pure type-II seesaw model is that the lepton-number-violating signatures induced by the heavy Majorana neutrinos can be discovered at the CERN Large Hadron Collider. We calculate the total cross section of the same-sign dilepton events pp→lα±Ni→lα±lβ±jj (for i=1,2i=1,2 and α,β=e,μ,τα,β=e,μ,τ), and emphasize the significant interference of the contributions from two different heavy Majorana neutrinos. The background from the standard model and the kinematic cuts used to reduce it have been considered. The possible way to distinguish between the signals from heavy Majorana neutrinos and those from doubly-charged Higgs bosons is briefly discussed.