Three-loop corrections to lamb shift in positronium: Electron factor and polarization

This is the authors' abstract. We don't add key points for this paper.

Hard spin-independent three-loop radiative contributions to energy levels in positronium generated by the two-photon-exchange diagrams with one-loop radiative insertions in the fermion lines and exchanged photons are calculated. This is a next step in calculations of all corrections of order m α 7 inspired by the new generation of precise 1 S − 2 S and 2 S − 2 P measurements in positronium.