Majorana Neutrinos Production at NLC in an Effective Approach
  We investigate the possibility of detecting Majorana neutrinos at the $e^+e^-$ Next Linear Collider (NLC). We study the $l_j^{\mp} l_k^{\mp} + jets$ ($l_j\equiv e ,\mu ,\tau$) final states which are, due to leptonic number violation, a clear signature for intermediate Majorana neutrino contributions. Such signals (final leptons of the same-sign) are not possible if the heavy neutrinos have Dirac nature. The interactions between Majorana neutrinos and the Standard Model (SM) particles are obtained from an effective Lagrangian approach. As for the background, we considered the SM reaction $e^+ e^- \rightarrow W^+W^+W^-W^-$, with two $W^\prime$s decaying into jets and two $W^\prime$s decaying into $l^{\pm}+\nu(\bar \nu)$, producing extra light neutrinos which avoid the detection. We present our results for the total cross-section as a function of the neutrino mass and the center of mass energies. We also show the discovery region as a function of the Majorana neutrino mass and the effective coupling. 
Javier Peressutti, Ismael Romero, Oscar Alfredo Sampayo
hep-ph