Is there a radio excess from the decoupling of pre-recombination bremsstrahlung?

Abstract

Recently it has been suggested that thermal bremsstrahlung emission, when it decouples prior to recombination, creates an excess over the Planck cosmic microwave background spectrum at sub-GHz frequencies. Remarkable by itself, this would also explain a long-standing unexplained deficit in the predictions of the extragalactic radio background. In this brief note we reiterate that no such non-thermal component can arise by itself when matter and radiation remain kinetically coupled.