Supernova bound on keV-mass sterile neutrinos reexamined

Abstract

Active-sterile neutrino mixing is strongly constrained for m_s > 100 keV to avoid excessive energy losses from supernova cores. For smaller m_s, matter effects suppress the effective mixing angle except for a resonant range of energies where it is enhanced. We study the case of nu_tau-nu_s-mixing where a nu_tau-barnu_tau asymmetry builds up due to the strong excess of nu_s over barnu_s emission or vice versa, reducing the overall emission rate. In the warm dark matter range m_s < 10 keV the mixing angle is essentially unconstrained.