Is there a Radio Excess from the Decoupling of Pre-recombination Bremsstrahlung?

Abstract

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, I reiterate that no such non-thermal component can arise by itself when matter and radiation remain kinetically coupled.