Impact of eV-mass sterile neutrinos on neutrino-driven supernova outflows

Motivated by recent hints for sterile neutrinos from the reactor anomaly, we study active-sterile conversions in a three-flavor scenario (2 active + 1 sterile families) for three different representative times during the neutrino-cooling evolution of the proto-neutron star born in an electron-capture supernova. In our early model (0.5 s post bounce), the nu(e)-nu(s) MSW effect driven by Delta m(2) = 2.35 eV(2) is dominated by ordinary matter and leads to a complete nu(e)-nu(s) swap with little or no trace of collective flavor oscillations. In our intermediate (2.9 s p.b.) and late models (6.5 s p.b.), neutrinos themselves significantly modify the nu(e)-nu(s) matter effect, and, in particular in the late model, nu nu refraction strongly reduces the matter effect, largely suppressing the overall nu(e)-nu(s) MSW conversion. This phenomenon has not been reported in previous studies of active-sterile supernova neutrino oscillations. We always include the feedback effect on the electron fraction Y-e due to neutrino oscillations. In all examples, Y-e is reduced and therefore the presence of sterile neutrinos can affect the conditions for heavy-element formation in the supernova ejecta, even if probably not enabling the r-process in the investigated outflows of an electron-capture supernova. The impact of neutrino-neutrino refraction is strong but complicated, leaving open the possibility that with a more complete treatment, or for other supernova models, active-sterile neutrino oscillations could generate conditions suitable for the r-process.