Signals for Majorana neutrinos in a $\gamma \gamma$ collider
  We study the possibilities to detect Majorana neutrinos in   $\gamma \gamma$ colliders for different center of mass energies.   We study the $W^\pm W^\pm l_j^{\mp} l_k^{\mp}$ ($l_j\equiv e ,\mu ,\tau$) final states which are, due to leptonic number violation, a clear signature for intermediate Majorana neutrino contribution. Such a signal (final dileptons of the same sign) is not possible if the heavy neutrinos are Dirac particles. We present our results for the total cross-section as a function of the neutrino mass and the center of mass energies. 
J.Peressutti and O.A.Sampayo