A Big-Bang Nucleosynthesis Limit on the Neutral Fermion Decays into
  Neutrinos
  Using the primordial helium abundance, an upper limit to the magnetic moments
for Dirac neutrinos had been provided by imposing restrictions on the number of
the additional helicity states. Considering non-thermal photons produced in the
decay of the heavy sterile mass eigenstates due to the neutrino magnetic
moment, we explore the constraints imposed by the observed abundances of all
the light elements produced during the Big Bang nucleosynthesis.
