Effects of active-sterile neutrino mixing during primordial
  nucleosynthesis
  In the present work, we discuss the effects of the inclusion of
sterile-active neutrino oscillations during the production of primordial
light-nuclei. We assume that the sterile neutrino mass-eigenstate might
oscillate with the two lightest active neutrino mass- eigenstates, with mixing
angles ${\phi}_1$ and ${\phi}_2$. We also allow a constant renormalization
(represented by a parameter (${\zeta}$)) of the sterile neutrino occupation
factor. Taking ${\zeta}$ and the mixing angles as free parameters, we have
computed distribution functions of active and sterile neutrinos and primordial
abundances. Using observable data we set constrains in the free parameters of
the model. It is found that the data on primordial abundances are consistent
with small mixing angles and with a value of ${\zeta}$ smaller than 0.65 at
3${\sigma}$ level.
