Production of $p$-nuclei from $r$-process seeds: the $\nu r$-process

TL;DR

This paper introduces the $ u r$-process, a new nucleosynthesis pathway on neutron-rich ejecta with intense neutrino flux, producing $p$-nuclei and $^{92}$Nb, differing from the standard $r$-process.

Contribution

It proposes the $ u r$-process as an alternative mechanism for $p$-nuclei production, highlighting the role of charged-current neutrino reactions in nucleosynthesis.

Findings

The $ u r$-process can produce $p$-nuclei and $^{92}$Nb.

Current models do not yet fulfill the conditions for the $ u r$-process.

Future models may realize the $ u r$-process in certain ejecta regions.

Abstract

We present a new nucleosynthesis process that may take place on neutron-rich ejecta experiencing an intensive neutrino flux. The nucleosynthesis proceeds similarly to the standard $r$-process, a sequence of neutron-captures and beta-decays, however with charged-current neutrino absorption reactions on nuclei operating much faster than beta-decays. Once neutron capture reactions freeze-out the produced $r$-process neutron-rich nuclei undergo a fast conversion of neutrons into protons and are pushed even beyond the $\beta$-stability line producing the neutron-deficient $p$-nuclei. This scenario, which we denote as the $\nu r$-process, provides an alternative channel for the production of $p$-nuclei and the short-lived nucleus $^{92}$Nb. We discuss the necessary conditions posed on the astrophysical site for the $\nu r$-process to be realized in nature. While these conditions are not fulfilled by current neutrino-hydrodynamic models of $r$-process sites, future models, including more complex physics and a larger variety of outflow conditions, may achieve the necessary conditions in some regions of the ejecta.