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Neutrino induced reactions are a basic ingredient in astrophysical processeslike star evolution. The existence of neutrino oscillations affects the rate ofnuclear electroweak decays which participates in the chain of events thatdetermines the fate of the star. Among the processes of interest, theproduction of heavy elements in core-collapse supernovae is strongly dependentupon neutrino properties, like the mixing between different species ofneutrinos. In this work we study the effects of neutrino oscillations upon theelectron fraction as a function of the neutrino mixing parameters, for twoschemes: the $1+1$ scheme (one active neutrino and one sterile neutrino) andthe $2+1$ scheme (two active neutrinos and one sterile neutrino). We haveperformed this analysis considering a core-collapse supernovae and determinedthe physical conditions needed to activate the nuclear reaction chains involvedin the r-process. We found that the interactions of the neutrinos with matterand among themselves and the initial amount of sterile neutrinos in theneutrino-sphere might change the electron fraction, therefore affecting theonset of the r-process. We have set constrains on the active-sterile neutrinomixing parameters. They are the square-mass-difference $\Delta m^2_{14} $, themixing angle $\sin^2 2\theta_{14}$, and the hindrance factor $\xi_s $ for theoccupation of sterile neutrinos. The calculations have been performed fordifferent values of $X_{\alpha}$, which is the fraction of $\alpha$-particles.For $X_{\alpha}=0$ the r-process is taking place if $\Delta m^2_{14} \geq 2 \,{\rm eV}^2 $, $\sin^2 2\theta_{14} < 0.8 $ and $\xi_s < 0.5$. For larger valuesof $X_{\alpha}$ the region of parameters is strongly reduced. The presentresults are compared to results available in the literature.

Neutrino induced reactions in core-collapse supernovae: effects on the electron fraction