# Dependence of weak interaction rates on the nuclear composition during stellar core collapse

## TL;DR

This study shows how nuclear composition and shell effects significantly influence weak interaction rates during stellar core collapse, affecting supernova modeling accuracy.

## Contribution

It demonstrates the impact of shell washout effects on weak rates and highlights the importance of NSE-like EOS in supernova simulations.

## Key findings

- Shell washout reduces electron capture rates by up to 20% early on and increases them by 40% later.
- Neutrino-nucleus scattering cross section decreases by approximately 15% due to shell effects.
- Single-nucleus approximation underestimates weak rates, especially in early phases.

## Abstract

We investigate the influences of the nuclear composition on the weak interaction rates of heavy nuclei during the core collapse of massive stars. The nuclear abundances in nuclear statistical equilibrium (NSE) are calculated by some equation of state (EOS) models including in-medium effects on nuclear masses. We systematically examine the sensitivities of electron capture and neutrino-nucleus scattering on heavy nuclei to the nuclear shell effects and the single nucleus approximation. We find that the washout of shell effects at high temperatures brings significant change to weak rates by smoothing the nuclear abundance distribution: the electron capture rate decreases by $\sim$20$\%$ in the early phase and increases by $\sim$40$\%$ in the late phase at most, while the cross section for neutrino-nucleus scattering is reduced by $\sim$15$\%$. This is because the open-shell nuclei become abundant instead of those with closed neutron shells as the shell effects disappear. We also find that the single-nucleus description based on the average values leads to underestimations of weak rates. Electron captures and neutrino coherent scattering on heavy nuclei are reduced by $\sim$80$\%$ in the early phase and by $\sim$5$\%$ in the late phase, respectively. These results indicate that NSE like EOS accounting for shell washout is indispensable for the reliable estimation of weak interaction rates in simulations of core-collapse supernovae.