Seeking Gauge Bileptons in Linear Colliders
  A promising direction to find physics beyond the standard model is to look for violation of $L_{e,\mu,\tau}$ conservation. In particular the process $e^- e^- \to \mu^- \mu^-$ with the exchange of a gauge bilepton has a striking signal without background and is predicted in the most economical model to have a cross-section an order of magnitude higher than previous estimates. 
Paul H. Frampton and Andrija Rasin