Scale of Mass Generation for Majorana Neutrinos

Scales of mass generation for Majorana neutrinos (as well as quarks and leptons) can be probed from high energy 2 → n inelastic scattering involving a multiple longitudinal gauge boson final state. We demonstrate that the unitarity of 2 → n scattering puts the strongest new upper limit on the scale of fermion mass generation, independent of the electroweak symmetry breaking scale v = ( √ 2GF ) − 1 2 . Strikingly, for Majorana neutrinos (quarks and leptons), we find that the strongest 2 → n limits fall in a narrow range, 136 − 170TeV (3 − 107TeV) with n = 20 − 24 (n = 2 − 12), depending on the observed fermion masses. Physical implications are discussed.