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 $SU(3)_{\rm c} \times SU(3)_{\rm L} \times U(1)$ model, the left-right $SU(2)_{\rm L} \times SU(2)_{\rm R} \times U(1)_{\rm B-L}$ one, and its supersymmetric version with doubly charged Higgs multiplets.Comment: 5 pages LaTeX + 1 postscript figure. Some references added; some new paragraphs added in the tex

Interplay of Non-Relativistic and Relativistic Effects in Neutrino Oscillations

A theoretical structure that involves neutrino mass eigenstates at non relativistic as well as relativistic energies is presented. Using this framework, we find that if the particle X, with mass 33.9 MeV, of the KARMEN collaboration anomaly is identified with the third neutrino mass eigenstate, then the present limit of 23 MeV upper bound on the tau neutrino mass implies |U_{\tau 3}| < 0.82.Comment: Revtex 3.0, 12 page