The unstable-neutrino expalantion for the reheating of the Universe, which accounts for the cosmic-background-radiation distortion, requires nonelectromagnetic fast decay of neutrinos and a small branching ratio to the channel including electromagnetically interacting particles. We show that there exists a simple particle-physics model which satisfies the conditions required for the reheating within the known family of particles (except for a massive neutrino). In this model the reheating is caused by the decay of ν’→ν$e^{+}$$e^{\mathrm{-}}$ and the dominant decay mode is given by ν’→ννν¯.

• Received 17 March 1989

DOI:https://doi.org/10.1103/PhysRevLett.63.585