Spin light of neutrino in matter and electromagnetic fields

A new type of electromagnetic radiation by a neutrino with non-zero magnetic (and/or electric) moment moving in background matter and electromagnetic field is considered. This radiation originates from the quantum spin flip transitions and we have named it as “spin light of neutrino” (SLν). The neutrino initially unpolarized beam (equal mixture of νL and νR) can be converted to the totally polarized beam composed of only νR by the neutrino spin light in matter and electromagnetic fields. The quasi-classical theory of this radiation is developed on the basis of the generalized Bargmann–Michel–Telegdi equation. The considered radiation is important for environments with high effective densities, n, because the total radiation power is proportional to n4. The spin light of neutrino, in contrast to the Cherenkov or transition radiation of neutrino in matter, does not vanish in the case of the refractive index of matter is equal to unit. The specific features of this new radiation are: (i) the total power of the radiation is proportional to γ4, and (ii) the radiation is beamed within a small angle δθ∼γ−1, where γ is the neutrino Lorentz factor. Applications of this new type of neutrino radiation to astrophysics, in particular to gamma-ray bursts, and the early universe should be important.