  We show how light spin-1/2 or spin-0 particles may be acceptable Dark Matter
candidates, provided they annihilate sufficiently strongly through new
interactions, such as those induced by a new light neutral spin-1 boson U. The
corresponding interaction is stronger than weak interactions at lower energies,
but weaker at higher energies.
  Annihilation cross sections of (axially coupled) spin-1/2 Dark Matter
particles, induced by a U vectorially coupled to matter, are the same as for
spin-0 particles. In both cases, the cross sections (sigma v_rel/c) into e+e-
automatically include a v_dm^2 suppression factor, as desirable to avoid an
excessive production of gamma rays from residual Dark Matter annihilations. We
also relate Dark Matter annihilations with production cross sections in e+e-
reactions. As for spin-0, light spin-1/2 Dark Matter particles annihilating
into e+e- could be responsible for the bright 511 keV gamma ray line observed
by INTEGRAL from the galactic bulge.
