Superheavy Majorana neutrino effects in the lepton-number violating e- + e- -> mu- + mu- process

In the minimal extension of the standard electroweak theory with ultra massive Majorana neutrinos, the process e- + e- -> mu- + mu- could be observable, in sharp contrast with the reaction e- + e- -> W- + W- which is entirely controlled by neutrinoless double beta decay $\beta {\beta }_{0\nu }$ data. Our result provides the process background that must be confronted “new physics” models which postulate doubly charged particles, such as the gauge bilepton Y^{-} in the $SU(3{)}_{\mathrm{c}}\times SU(3{)}_{\mathrm{L}}\times U(1)$ model, the left-right $SU(2{)}_{\mathrm{L}}\times SU(2{)}_{\mathrm{R}}\times U(1{)}_{\mathrm{B}-\mathrm{L}}$ one, and its supersymmetric version with doubly charged Higgs multiplets.