Neutrino-Induced Nucleosynthesis in Helium Shells of Early Core-Collapse Supernovae

We summarize our studies on neutrino-driven nucleosynthesis in He shells of early core-collapse supernovae with metallicities of $Z\lesssim 10^{-3},Z_\odot$\mathrm{.}Wefindthatforprogenitorsof$\sim 11$--$15,{\rm M}_\odot$,theneutronsreleasedby$^4{\rm He}(\bar{\nu}_e,e^+n)^3{\rm H}$ in He shells can be captured to produce nuclei with mass numbers up to $A \sim 200$. This mechanism is sensitive to neutrino emission spectra and flavor oscillations. In addition, we find two new primary mechanisms for neutrino-induced production of ${}^9$Be in He shells. The first mechanism produces ${}^9$Be via $^7{\rm Li}(n,\gamma)^8{\rm Li}(n,\gamma)^9{\rm Li}(e^-\bar{\nu}e)^9{\rm Be}$ and relies on a low explosion energy for its survival. The second mechanism operates in progenitors of $\sim 8,{\rm M}\odot$,where$^9$Becanbeproduceddirectlyvia$^7{\rm Li}(^3{\rm H},n_0)^9{\rm Be}$ during the rapid expansion of the shocked He-shell material. The light nuclei ${}^7$Li and ${}^3$H involved in these mechanisms are produced by neutrino interactions with ${}^4$He. We discuss the implications of neutrino-induced nucleosynthesis in He shells for interpreting the elemental abundances in metal-poor stars.