  Sneutrino-antisneutrino mixing occurs in a supersymmetric model where
neutrinos have nonzero Majorana masses. This can lead to the sneutrino decaying
into a final state with a "wrong-sign charged lepton". In an $e^- \gamma$
collider, the signal of the associated production of an electron-sneutrino and
the lighter chargino and their subsequent decays can be $e^- \gamma \to e^+
{\tilde \tau}_1^- {\tilde \tau}_1^- + \mpT$ where the ${\tilde \tau}_1$s are
long-lived and can produce heavily ionizing charged tracks. This signal is free
of any Standard Model background, and the supersymmetric backgrounds are small.
Such a signal can be experimentally observable under certain conditions which
are possible to obtain in an anomaly-mediated supersymmetry breaking scenario.
Information on a particular combination of the neutrino masses and mixing
angles can also be extracted through the observation of this signal.
Sneutrino-antisneutrino mixing at the LHC is currently under study, and
asymmetry considerations seem promising there.
