  Given the eventuality of neutrino and muon factories in the foreseeable
future, all possible 2-to-2 processes involving two neutrinos, whether Dirac or
Majorana ones, and two charged fermions are considered on the basis of the most
general Lorentz invariant four-fermion effective interaction possible, in the
limit of massless particles. Such a parametrization should enable the
assessment of the sensitivity to physics beyond the Standard Model, including
the eventual discrimination between the Dirac or Majorana character of
neutrinos, of specific experimental beam and detector designs.
