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Register a new userEffects of the Metallicity on Li and B Production in Supernova Neutrino Process
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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.
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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.
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.
Long-lived radioactive nuclei play an important role as nucleo-cosmochronometers and as cosmic tracers of nucleosynthetic source activity. In particular nuclei in the actinide region like thorium, uranium, and plutonium can testify to the enrichment of an environment by the still enigmatic astrophysical sources that are responsible for the production of neutron-rich nuclei by the rapid neutron-capture process (r-process). Supernovae and merging neutron-star (NS) or NS-black hole binaries are considered as most likely sources of the r-nuclei. But arguments in favour of one or the other or both are indirect and make use of assumptions; they are based on theoretical models with remaining simplifications and shortcomings. An unambiguous observational determination of a production event is still missing. In order to facilitate searches in this direction, e.g. by looking for radioactive tracers in stellar envelopes, the interstellar medium or terrestrial reservoirs, we provide improved theoretical estimates and corresponding uncertainty ranges for the actinide production ($^{232}$Th, $^{235,236,238}$U, $^{237}$Np, $^{244}$Pu, and $^{247}$Cm) in neutrino-driven winds of core-collapse supernovae. Since state-of-the-art supernova models do not yield r-process viable conditions ---but still lack, for example, the effects of strong magnetic fields--- we base our investigation on a simple analytical, Newtonian, adiabatic and steady-state wind model and consider the superposition of a large number of contributing components, whose nucleosynthesis-relevant parameters (mass weight, entropy, expansion time scale, and neutron excess) are constrained by the assumption that the integrated wind nucleosynthesis closely reproduces the solar system distribution of r-process elements. We also test the influence of uncertain nuclear physics.
Recently, it has been demonstrated that neutrinos in a supernova oscillate collectively. This process occurs much deeper than the conventional matter-induced MSW effect and hence may have an impact on nucleosynthesis. In this paper we explore the effects of collective neutrino oscillations on the r-process, using representative late-time neutrino spectra and outflow models. We find that accurate modeling of the collective oscillations is essential for this analysis. As an illustration, the often-used single-angle approximation makes grossly inaccurate predictions for the yields in our setup. With the proper multiangle treatment, the effect of the oscillations is found to be less dramatic, but still significant. Since the oscillation patterns are sensitive to the details of the emitted fluxes and the sign of the neutrino mass hierarchy, so are the r-process yields. The magnitude of the effect also depends sensitively on the astrophysical conditions - in particular on the interplay between the time when nuclei begin to exist in significant numbers and the time when the collective oscillation begins. A more definitive understanding of the astrophysical conditions, and accurate modeling of the collective oscillations for those conditions, is necessary.
The spectrum of the supernova relic neutrino (SRN) background from past stellar collapses including black hole formation (failed supernovae) is calculated. The redshift dependence of the black hole formation rate is considered on the basis of the metallicity evolution of galaxies. Assuming the mass and metallicity ranges of failed supernova progenitors, their contribution to SRNs is quantitatively estimated for the first time. Using this model, the dependences of SRNs on the cosmic star formation rate density, shock revival time and equation of state are investigated. The shock revival time is introduced as a parameter that should depend on the still unknown explosion mechanism of core collapse supernovae. The dependence on equation of state is considered for failed supernovae, whose collapse dynamics and neutrino emission are certainly affected. It is found that the low-energy spectrum of SRNs is mainly determined by the cosmic star formation rate density. These low-energy events will be observed in the Super-Kamiokande experiment with gadolinium-loaded water.
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