Astrophysical information from the Rayleigh-Jeans Tail of the CMB
  One of the explanations for the recent EDGES-LOW band 21-cm measurements of a
strong absorption signal around 80~MHz is the presence of an excess radio
background to the Cosmic Microwave Background (CMB). Such excess can be
produced by the decay of unstable particles into small mass dark photons which
have a non-zero mixing angle with electromagnetism. We use the EDGES-LOW band
measurements to derive joint constraints on the properties of the early
galaxies and the parameters of such a particle physics model for the excess
radio background. A Bayesian analysis shows that a high star formation
efficiency and X-ray emission of $4-7 \times 10^{48} ~\rm erg$ per solar mass
in stars are required along with a suppression of star formation in halos with
virial temperatures $\lesssim 2\times 10^4$ K. The same analysis also suggests
a 68 percent credible intervals for the mass of the decaying dark matter
particles, it's lifetime, dark photon mass and the mixing angle of the dark and
ordinary photon oscillation of $[10^{-3.5}, 10^{-2.4}]$ eV, $[10^{1.1},
10^{2.7}]\times 13.8 ~\rm Gyr$, $[10^{-12.2}, 10^{-10}]$ eV and $[10^{-7},
10^{-5.6}]$ respectively. This implies an excess radio background which is
$\approx 5.7$ times stronger than the CMB around 80~MHz. This value is a factor
$\sim 3$ higher than the previous predictions which used a simplified model for
the 21-cm signal.
