Testing the Realistic Seesaw Model with Two Heavy Majorana Neutrinos at the CERN Large Hadron Collider

TL;DR

This paper proposes a flavor symmetry-based scenario within the seesaw model where heavy Majorana neutrinos produce detectable lepton-number-violating signals at the LHC, with distinctive interference effects and potential to differentiate from other new physics signals.

Contribution

It introduces a novel seesaw scenario with structural cancellation due to flavor symmetry, leading to observable collider signatures of heavy Majorana neutrinos.

Findings

Heavy Majorana neutrinos can produce detectable same-sign dilepton signals at the LHC.

Interference effects between two heavy neutrinos significantly impact the collider signatures.

The scenario allows distinguishing signals from heavy neutrinos versus doubly-charged Higgs bosons.

Abstract

In the conventional type-(I+II) seesaw model, the effective mass matrix of three known light neutrinos is given by M_nu = M_L - M_D M^{-1}_R M^T_D in the leading-order approximation. We propose an intriguing scenario, in which the structural cancellation condition M_D M^{-1}_R M^T_D = 0 is guaranteed by the A_4 x Z_2 flavor symmetry. As a consequence, neutrino masses are mainly generated by the Higgs triplet M_nu = M_L, 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 to l^+(-)_alpha N_i to l^+(-)_alpha l^+(-)_beta jj (for i=1, 2 and alpha, beta = e, mu, tau), 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.