Dark matter sterile neutrinos in stellar collapse: Alteration of energy/lepton number transport, and a mechanism for supernova explosion enhancement

We investigate matter-enhanced Mikheyev-Smirnov-Wolfenstein (MSW) active-sterile neutrino conversion in the nu(e)-><-nu(s) channel in the collapse of the iron core of a presupernova star. For values of sterile neutrino rest mass m(s) and vacuum mixing angle theta (specifically, 0.5 keV < m(s)< 10 keV and sin(2)2 theta > 5x10(-12)) which include those required for viable sterile neutrino dark matter, our one-zone in-fall phase collapse calculations show a significant reduction in core lepton fraction. This would result in a smaller homologous core and therefore a smaller initial shock energy, disfavoring successful shock reheating and the prospects for an explosion. However, these calculations also suggest that the MSW resonance energy can exhibit a minimum located between the center and surface of the core. In turn, this suggests a post-core-bounce mechanism to enhance neutrino transport and neutrino luminosities at the core surface and thereby augment shock reheating: (1) scattering-induced or coherent MSW nu(e)->nu(s) conversion occurs deep in the core, at the first MSW resonance, where nu(e) energies are large (similar to 150 MeV); (2) the high energy nu(s) stream outward at near light speed; (3) they deposit their energy when they encounter the second MSW resonance nu(s)->nu(e) just below the proto-neutron star surface.