Effects of Hoyle state de-excitation on νp–process nucleosynthesis and Galactic chemical evolution

The particle-induced hadronic de-excitation of the Hoyle state in ¹²C induced by inelastic scattering in a hot and dense plasma can enhance the triple-alpha reaction rate. This prevents the production of heavy nuclei within the neutrino-driven winds of core-collapse supernovae and raises a question as to the contribution of proton-rich neutrino-driven winds as the origin of p–nuclei in the solar-system abundances. Here we study νp-process nucleosynthesis in proton-rich neutrino-driven winds relevant to the production of Mo92,94 and Ru96,98 by considering such particle-induced de-excitation. We find that the enhanced triple-alpha reaction rate induced by proton inelastic scattering can increase the production of Mo92,94 and Ru96,98 in an energetic hypernova wind model with a massive proto-neutron star although the abundances of these p–nuclei decrease in a wind model of ordinary core-collapse supernovae. The enhancement of the triple-alpha reaction rate induced by the neutron scattering hardly affects the νp-process at low temperature. We show the new result that, contrary to the results for ordinary core-collapse supernovae, the hypernova νp-process can contribute to the Galactic chemical evolution of p–nuclei regardless of the particle-induced Hoyle state de-excitation and even enhance the solar isotopic fractions of Mo92,94 and Ru96,98.