Relic neutrino decay solution to the excess radio background

Abstract

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 νi into a sterile neutrino νs, 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 τi=1.46×1021s and Δmi=4.0×10−5eV, where τi is the lifetime and Δmi is the mass difference between the decaying active neutrino and the sterile neutrino. On the other hand, if relic neutrino decays do not explain ARCADE 2 data, then these place a stringent constraint $\D m_i^{3/2} \tau_i \gtrsim 2 \times 10^{14}\,{\rm eV}^{3/2}\,{\rm s}$ in the range $1.4 \times 10^{-5} \, {\rm eV} < \D m_i < 2.5 \times 10^{-4}\,{\rm eV}$. The solution also predicts a stronger 21 cm absorption global signal than the predicted one from the ŁCDM model, with a contrast brightness temperature T21=−238+21−20mK (99% C.L.) at redshift z≃17. This is in mild tension with the even stronger signal found by the EDGES collaboration, T21=−500+200−500mK, suggesting that this might have been overestimated, maybe receiving a contribution from some unidentified foreground source.

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