Abstract
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 ν_i (either i=1,
or i=2, or i=3) into a sterile neutrino ν_ 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 τ_i = 1.46 × 10^21 s and Δ m_i = 4.0 × 10^-5
eV, where τ_i is the lifetime and Δ m_i 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 Δ m_i^3/2τ_i
≳ 2 × 10^14 eV^3/2 s in the range 1.4 × 10^-5 eV<Δ m_i < 2.5 × 10^-4 eV. The solution also predicts a stronger 21 cm
absorption global signal than the predicted one from the ΛCDM model, with a contrast
brightness temperature T_21 = -238^+21_-20 mK (99% C.L.) at redshift z≃
17. This is in mild tension with the even stronger signal found by the EDGES collaboration,
T_21 = - 500^+200_-500 mK, suggesting that this might have been overestimated,
possibly receiving a contribution from some unidentified foreground source.