  In addition to the problem of galaxy formation, one of the greatest open
questions of cosmology is represented by the existence of an asymmetry between
matter and antimatter in the baryonic component of the Universe. We believe
that a net lepton number for the three neutrino species can be used to
understand this asymmetry. This also implies an asymmetry in the
matter-antimatter component of the leptons. The existence of a nonnull lepton
number for the neutrinos can easily explain a cosmological abundance of
neutrinos consistent with the one needed to explain both the rotation curves of
galaxies and the flatness of the Universe. Some propedeutic results are
presented in order to attack this problem.
