Cross sections involving massive Dirac or Majorana neutrinos usually differ only by terms which are suppressed by the smallness of the neutrino mass. The process $e^+e^-\to\nu\nu$, however, is an example in which the two differential cross sections are quite distinct even in the limit $m_\nu\to 0$ as long as $m_\nu\not=0$. I discuss the cause of this phenomenon and comment on strategies to identify processes with quite different Majorana and Dirac neutrino signals.
Categories: hep-ph