A NEW HYPERFINE OPERATOR IN THE DIRAC-EQUATION

A recently found additional hyperfine interaction in the Dirac equatio n extends the validity of this equation to comparable masses of its tw o spin-1/2 particles. For equal masses as in positronium, it ensures C P conservation. The new operator simplifies the hyperfine mixing of st ates with different j. Anomalous magnetic moments are incorporated, an d an application to helium-like Rydberg states is mentioned. CPT invar iance is demonstrated and discussed, including the extension to n-elec tron atoms.