  Photo-absorption in fully ionized plasmas in high magnetic fields is
re-examined, using the methods of many-body quantum field theory. For
frequencies in the immediate vicinity of the electron cyclotron resonance the
rates we obtain disagree markedly from those in the literature. The new element
in our work that causes most of the disagreement is the inclusion of the lowest
order real part of the energy-shift of the resonant state, where, in effect,
previous authors had included only the imaginary part. In a region around and
below the proton cyclotron resonance our results also disagree with those of
previous authors, for a number of reasons.
