Search for Radiative Decays of Cosmic Background Neutrino using Cosmic Infrared Background Energy Spectrum

We propose to search for the neutrino radiative decay by fitting a photon energy spectrum of the cosmic infrared background to a sum of the photon energy spectrum from the neutrino radiative decay and a continuum. By comparing the present cosmic infrared background energy spectrum observed by AKARI and Spitzer to the photon energy spectrum expected from neutrino radiative decay with a maximum likelihood method, we obatined a lifetime lower limit of 3.1 × 10¹² to 3.8 × 10¹² years at 95% confidence level for the third generation neutrino ν₃ in the ν₃ mass range between 50 and 150 meV/c² under the present constraints by the neutrino oscillation measurements. In the left--right symmetric model, the minimum lifetime of ν₃ is predicted to be 1.5 × 10¹⁷ years for m₃ of 50 meV/c². We studied the feasibility of the observation of the neutrino radiative decay with a lifetime of 1.5 × 10¹⁷ years, by measuring a continuous energy spectrum of the cosmic infrared background.