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Register a new userNeutrino self-interaction and MSW effects on the supernova neutrino-process
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We calculate the abundances of $^{7}$Li, $^{11}$B, $^{92}$Nb, $^{98}$Tc, $^{138}$La, and $^{180}$Ta produced by neutrino $( u)$ induced reactions in a core-collapse supernova explosion. We consider the modification by $ u$ self-interaction ($ u$-SI) near the neutrinosphere and the Mikheyev-Smirnov-Wolfenstein effect in outer layers for time-dependent neutrino energy spectra. Abundances of $^{7}$Li and heavy isotopes $^{92}$Nb, $^{98}$Tc and $^{138}$La are reduced by a factor of 1.5-2.0 by the $ u$-SI. In contrast, $^{11}$B is relatively insensitive to the $ u$-SI. We find that the abundance ratio of heavy to light nucleus, $^{138}$La/$^{11}$B, is sensitive to the neutrino mass hierarchy, and the normal mass hierarchy is more likely to be consistent with the solar abundances.
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We reinvestigate effects of neutrino oscillations on the production of 7Li and 11B in core-collapse supernovae (SNe). During the propagation of neutrinos from the proto-neutron star, their flavors change and the neutrino reaction rates for spallation of 12C and 4He are affected. In this work corrected neutrino spallation cross sections for 4He and 12C are adopted. Initial abundances involving heavy s-nuclei and other physical conditions are derived in a new calculation of the SN 1987A progenitor in which effects of the progenitor metallicity are included. A dependence of the SN nucleosynthesis and final yields of 7Li and 11B on the neutrino mass hierarchy are shown in several stellar locations. In the normal hierarchy case, the charged current reaction rates of electron neutrinos are enhanced, and yields of proton-rich nuclei, along with 7Be and 11C, are increased. In the inverted hierarchy case, the charged current reaction rates of electron antineutrinos are enhanced, and yields of neutron-rich nuclei, along with 7Li and 11B, are increased. We find that variation of the metallicity modifies the yields of 7Li, 7Be, 11B, and 11C. This effect is caused by changes in the neutron abundance during SN nucleosynthesis. Therefore, accurate calculations of Li and B production in SNe should take into account the metallicity of progenitor stars.
Flavor transitions in supernova neutrinos are yet to be determined. We present a method to probe whether or not the Mikheyev-Smirnov-Wolfenstein effects occur as SN neutrinos propagate outward from the SN core by investigating time evolutions of neutrino event rates for different flavors in different kinds of detectors. As the MSW effect occurs, the $ u_e$ flux swaps with the $ u_x$ flux, which represents any one of $ u_{mu}$, $ u_{tau}$, $bar{ u}_{mu}$, and $bar{ u}_{tau}$ flux, either fully or partially depending on the neutrino mass hierarchy. During the neutronization burst, the $ u_e$ emission evolves in a much different shape from the emissions of $bar{ u}_e$ and $ u_x$ while the latter two evolve in a similar pattern. Meanwhile, the luminosity of the the $ u_e$ emission is much larger than those of the $bar{ u}_e$ and $ u_x$ emissions while the latter two are roughly equal. As a consequence, the time-evolution pattern of the $ u_e{rm Ar}$ event rates in the absence of the MSW effect will be much different from that in the occurrence of the MSW effect, in either mass hierarchy. With the simulated SN neutrino emissions, the $ u_e{rm Ar}$ and inverse beta decay event rates are evaluated. The ratios of the two cumulative event rates are calculated for different progenitor masses up to $100~{rm ms}$. We show that the time evolutions of this cumulative ratios can effectively determine whether MSW effects really occur for SN neutrinos or not.
The neutrino process ($ u$-process) for the production of 7Li and 11B in core-collapse supernovae (SNe) is extensively investigated. Initial abundances of s-nuclei and other physical conditions are derived from an updated calculation of the SN 1987A progenitor. The nuclear reaction network including neutrino reactions is constructed with the variable order Bader-Deuflhard integration method. We find that yields of 7Li and 11B significantly depend on the stellar metallicity while they are independent of the weak s-process during the stellar evolution. When the metallicity is high, there are more neutron absorbers, i.e., 56Fe, 14N (from initial CNO nuclei), and 54Fe, and the neutron abundance is small during the $ u$-process. Since 7Be is predominantly destroyed via 7Be(n,p)7Li, a change in the neutron abundance results in different 7Be yields. Then, the calculated yield ratio 7Li/11B=0.93 for the solar metallicity is larger than that for the SN 1987A 7Li/11B=0.80 by 16 % in the inverted mass hierarchy case. We analyze contributions of respective reactions as well as abundance evolution, and clarify the $ u$-process of 7Li and 11B.
Adopting the 3+1 neutrino mixing parameters by the IceCube and shortbase line experiments, we investigate the sterile-active neutrino oscillation effects on the supernova neutrino process. For the sterile neutrino ($ u_s$), we study two different luminosity models. First, we presume that the $ u_s$ does not interact with other particles through the standard interactions apart from the oscillation with the active neutrinos. Second, we consider that $ u_s$ can be directly produced by $ u_e$ scattering with matter. In both cases, we find that the pattern of neutrino oscillations can be changed drastically by the $ u_s$ in supernova environments. Especially multiple resonances occur, and consequently affect thermal neutrino-induced reaction rates. As a result, $^7$Li, $^7$Be, $^{11}$B, $^{11}$C, $^{92}$Nb, $^{98}$Tc and $^{138}$La yields in the $ u$-process are changed. Among those nuclei, $^7$Li and $^{11}$B yields can be constrained by the analysis of observed SiC X grains. Based on the meteoritic data, we conclude that the second model can be allowed while first model is excluded. The viability of the second model depends on the sterile neutrino temperature and the neutrino mass hierarchy.
Binary interactions, especially mass transfer and mergers, can strongly influence the evolution of massive stars and change their final properties and the occurrence of supernovae. Here, we investigate how binary interactions affect predictions of the diffuse flux of neutrinos. By performing stellar population syntheses including prescriptions for binary interactions, we show that the resulting detection rates of the diffuse supernova neutrino background is enhanced by 15%-20% compared to estimates without binary considerations. A source of significant uncertainty arises due to the presently sparse knowledge of the evolution of rapidly rotating carbon-oxygen cores, especially those created as a result of mergers near the white dwarf to core collapse boundary. The enhancement effect may be as small as a few percent if the effects of rotation in postmerger systems are neglected, or as large as 75% if trends are extrapolated. Our estimates serve to highlight that binary effects can be important.
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