Relic neutrino decay solution to the excess radio background

Understand

The excess radio background detected by ARCADE 2 represents a puzzle within the standard cosmological model.

• There is no clear viable astrophysical solution, and therefore, it might indicate the presence of new physics.
• Radiative decays of a relic neutrino $\nu_i$ (either $i=1$, or $i=2$, or $i=3$) into a sterile neutrino $\nu_{\rm s}$, assumed to be quasi-degenerate, provide a solution that currently evades all constraints posed by different cosmological observations and reproduces very well the ARCADE 2 data.
• We find a very good fit to the ARCADE 2 data with best fit values $\tau_i = 1.46 \times 10^{21}\,{\rm s}$ and $\Delta m_i = 4.0 \times 10^{-5}\,{\rm eV}$, where $\tau_i$ is the lifetime and $\Delta m_i$ is the mass difference between the decaying active neutrino and the sterile neutrino.