$e^- e^-$ Collisions Mediated by Composite Neutrinos

The lepton number violating process, $e^- e^- \to W^- W^-$ has been widely discussed in the Majorana neutrino exchange mechanism. Here, we discuss this process in a composite neutrino model where excited Majorana neutrinos are exchanged. We found several qualitatively different features from the neutrino exchange case: (1) The longitudinally polarized $W$'s are not produced, (2) the neutrinoless double beta decay does not constrain much and a much larger cross section is expected, and (3) CP violating phases may be explored because all excited neutrinos are heavy so that large mixings among them are expected.