On a possible nonequilibrium imprint in the cosmic background at low
  frequencies
  The cosmic background radiation has been observed to deviate from the Planck
law expected from a blackbody at $\sim$ 2.7 K at frequencies below $\sim 3$
GHz. We discuss the abundance of the low-energy photons from the perspective of
nonequilibrium statistical mechanics. We propose a mechanism of stochastic
frequency-diffusion, the counterpart to stochastic acceleration for charged
particles in a turbulent plasma, to modify the standard Kompaneets equation.
The resulting violation of the Einstein relation allows to take advantage of
low-frequency localization and finally leads to photon cooling. The new
equation predicts a frequency distribution in agreement with the absolute
temperature measurements of the cosmic background radiation down to about 20
MHz, for which we offer here an updated compilation. In that sense, the so
called 'space roar' we observe today is interpreted as a nonequilibrium echo of
the early universe, and of nonequilibrium conditions in the primordial plasma
more specifically.
