Scale of Mass Generation for Majorana Neutrinos

Abstract

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 $v=(\sqrt{2}G_F)^{-1/2}$. Strikingly, for Majorana neutrinos (quarks and leptons), we find that the strongest 2 --> n limits fall in a narrow range, 136-170 TeV (3-107 TeV) with n=20-24 (n=2-12), depending on the observed fermion masses. Physical implications are discussed.