Sterile Neutrinos in Astrophysical Environments : Big Bang Nucleosynthesis and Supernova Neutrino Process

In spite of a great success in the discovery of neutrino oscillations, an inconsistency between the three neutrino model and observed neutrino data has left a problem called "neutrino anomalies". The sterile neutrino, as a hypothetical particle, is coined to resolve the anomalies. Although the obscurity of nuclear reactions in reactors should be explained, the sterile neutrino, as a possible solution, has attracted intensive discussions. Especially the role of sterile neutrinos has been importantly discussed in the astrophysics as well as the neutrino physics. In this proceeding, we review how the sterile neutrino affects two astrophysical environments; one is big bang nucleosynthesis (BBN) and the other is supernova (SN) neutrino process.