NEUTRINO-DRIVEN EXPLOSION OF A 20 SOLAR-MASS STAR IN THREE DIMENSIONS ENABLED BY STRANGE-QUARK CONTRIBUTIONS TO NEUTRINO–NUCLEON SCATTERING

Abstract

Interactions with neutrons and protons play a crucial role for the neutrino\nopacity of matter in the supernova core. Their current implementation in many\nsimulation codes, however, is rather schematic and ignores not only\nmodifications for the correlated nuclear medium of the nascent neutron star,\nbut also free-space corrections from nucleon recoil, weak magnetism or strange\nquarks, which can easily add up to changes of several 10% for neutrino energies\nin the spectral peak. In the Garching supernova simulations with the\nPrometheus-Vertex code, such sophistications have been included for a long time\nexcept for the strange-quark contributions to the nucleon spin, which affect\nneutral-current neutrino scattering. We demonstrate on the basis of a 20 M_sun\nprogenitor star that a moderate strangeness-dependent contribution of g_a^s =\n-0.2 to the axial-vector coupling constant g_a = 1.26 can turn an unsuccessful\nthree-dimensional (3D) model into a successful explosion. Such a modification\nis in the direction of current experimental results and reduces the\nneutral-current scattering opacity of neutrons, which dominate in the medium\naround and above the neutrinosphere. This leads to increased luminosities and\nmean energies of all neutrino species and strengthens the neutrino-energy\ndeposition in the heating layer. Higher nonradial kinetic energy in the gain\nlayer signals enhanced buoyancy activity that enables the onset of the\nexplosion at ~300 ms after bounce, in contrast to the model with vanishing\nstrangeness contributions to neutrino-nucleon scattering. Our results\ndemonstrate the close proximity to explosion of the previously published,\nunsuccessful 3D models of the Garching group.\n