Supernova simulations to date have assumed that during core collapse electron captures occur dominantly on free protons, while captures on heavy nuclei are Pauli-blocked and are ignored. We have calculated rates for electron capture on nuclei with mass numbers A = 65-112 for the temperatures and densities appropriate for core collapse. We find that these rates are large enough so that, in contrast to previous assumptions, electron capture on nuclei dominates over capture on free protons. This leads to significant changes in core collapse simulations. PACS numbers: 26.50.+x, 97.60.Bw, At the end of their lives, stars with masses exceeding roughly 10 M ⊙ reach a moment in their evolution when their iron core provides no further source of nuclear energy generation. At this time, they collapse and, if not too massive, bounce and explode in spectacular events known as type II or Ib/c supernovae. As the density, ρ, of the star's center increases, electrons become more degenerate and their chemical potential µ e grows (µ e ∼ ρ 1/3 ). For sufficiently high values of the chemical potential electrons are captured by nuclei producing neutrinos, which for densities 10 11 g cm −3 , freely escape from the star, removing energy and entropy from the core. Thus the entropy stays low during collapse ensuring that nuclei dominate in the composition over free protons and neutrons. During the presupernova stage, i.e. for core densities 10 10 g cm −3 and proton-to-nucleon ratios Y e 0.42, nuclei with A = 55-65 dominate. The relevant rates for weak-interaction processes (including β ± decay and electron and positron capture) were first estimated by Fuller, Fowler and Newman [1] (for nuclei with A < 60), considering that at such conditions allowed (Fermi and Gamow-Teller) transitions dominate. The rates have been recently improved based on modern data and state-of-the-art many-body models [2], considering nuclei with A = 45-65. (This rate set will be denoted LMP in the following.) Presupernova models utilizing these improved weak rates are presented in [3]. In collapse simulations, i.e. densities 10 10 g cm −3 , a much simpler description of electron capture on nuclei is used. Here the rates are estimated in the spirit of the independent particle model (IPM), assuming pure Gamow-Teller (GT) transitions and considering only single particle states for proton and neutron numbers be- During core collapse, temperatures and densities are high enough to ensure that nuclear statistical equilibrium (NSE) is achieved. This means that for sufficiently low entropies, the matter composition is dominated by the nuclei with the highest binding energy for a given Y e . Electron capture reduces Y e , driving the nuclear composition to more neutron rich and heavier nuclei, including those with N > 40, which dominate the matter composition for densities larger than a few 10 10 g cm −3 . As a consequence of the model applied in previous collapse simulations, electron capture on nuclei ceases at these densities and the capture is entirely due to free proto...

The most important weak nuclear interaction to the dynamics of stellar core collapse is electron capture, primarily on nuclei with masses larger than 60. In prior simulations of core collapse, electron capture on these nuclei has been treated in a highly parameterized fashion, if not ignored. With realistic treatment of electron capture on heavy nuclei come significant changes in the hydrodynamics of core collapse and bounce. We discuss these as well as the ramifications for the post-bounce evolution in core collapse supernovae.

Electron captures on nuclei play an important role in the dynamics of the collapsing core of a massive star that leads to a supernova explosion. Recent calculations of these capture rates were based on microscopic models which account for relevant degrees of freedom. Due to computational restrictions such calculations were limited to a modest number of nuclei, mainly in the mass range A = 45-110. Recent supernova simulations show that this pool of nuclei, however, omits the very neutron-rich and heavy nuclei which dominate the nuclear composition during the last phase of the collapse before neutrino trapping. Assuming that the composition is given by Nuclear Statistical Equilibrium we present here electron capture rates for collapse conditions derived from individual rates for roughly 2700 individual nuclei. For those nuclei which dominate in the early stage of the collapse, the individual rates are derived within the framework of microscopic models, while for the nuclei which dominate at high densities we have derived the rates based on the Random Phase Approximation with a global parametrization of the single particle occupation numbers. In addition, we have improved previous rate evaluations by properly including screening corrections to the reaction rates into account.

We study neutral current neutrino-nucleus reaction cross-sections for Mn, Fe, Co and Ni isotopes. An earlier study for a few selected nuclei has shown that in the supernova environment the cross sections are increased for low energy neutrinos due to finite-temperature effects. Our work supports this finding for a much larger set of nuclei. Furthermore we extend previous work to higher neutrino energies considering allowed and forbidden multipole contributions to the cross sections. The allowed contributions are derived from large-scale shell model calculations of the Gamow-Teller strength, while the other multipole contributions are calculated within the Random Phase Approximation. We present the cross sections as functions of initial and final neutrino energies and for a range of supernova-relevant temperatures. These cross sections will allow improved estimates of inelastic neutrino reactions on nuclei in supernova simulations.

Based on the shell model for Gamow-Teller and the random phase approximation for forbidden transitions, we calculate cross sections for inelastic neutrino-nucleus scattering (INNS) under supernova (SN) conditions, assuming a matter composition given by nuclear statistical equilibrium. The cross sections are incorporated into state-of-the-art stellar core-collapse simulations with detailed energy-dependent neutrino transport. While no significant effect on the SN dynamics is observed, INNS increases the neutrino opacities noticeably and strongly reduces the high-energy tail of the neutrino spectrum emitted in the neutrino burst at shock breakout. Relatedly the expected event rates for the observation of such neutrinos by earthbound detectors are reduced by up to about 60%.