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

TL;DR

This paper investigates how neutrino oscillations, especially involving sterile neutrinos, influence the electron fraction in core-collapse supernovae, affecting heavy element synthesis via the r-process and constraining neutrino mixing parameters.

Contribution

It provides a detailed analysis of neutrino oscillation effects on the electron fraction in supernovae, introducing new constraints on active-sterile neutrino mixing parameters relevant for nucleosynthesis.

Findings

Neutrino interactions and initial sterile neutrino content can alter the electron fraction.

Constraints on neutrino mixing parameters: Δm²₁₄ ≥ 2 eV², sin²2θ₁₄ < 0.8, ξ_s < 0.5.

The parameter space for r-process activation is reduced with higher alpha-particle fractions.

Abstract

Neutrino induced reactions are a basic ingredient in astrophysical processes like star evolution. The existence of neutrino oscillations affects the rate of nuclear electroweak decays which participates in the chain of events that determines the fate of the star. Among the processes of interest, the production of heavy elements in core-collapse supernovae is strongly dependent upon neutrino properties, like the mixing between different species of neutrinos. In this work we study the effects of neutrino oscillations upon the electron fraction as a function of the neutrino mixing parameters, for two schemes: the $1+1$ scheme (one active neutrino and one sterile neutrino) and the $2+1$ scheme (two active neutrinos and one sterile neutrino). We have performed this analysis considering a core-collapse supernovae and determined the physical conditions needed to activate the nuclear reaction chains involved in the r-process. We found that the interactions of the neutrinos with matter and among themselves and the initial amount of sterile neutrinos in the neutrino-sphere might change the electron fraction, therefore affecting the onset of the r-process. We have set constrains on the active-sterile neutrino mixing parameters. They are the square-mass-difference $\Delta m^2_{14} $, the mixing angle $\sin^2 2\theta_{14}$, and the hindrance factor $\xi_s $ for the occupation of sterile neutrinos. The calculations have been performed for different 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 values of $X_{\alpha}$ the region of parameters is strongly reduced. The present results are compared to results available in the literature.