Three-Loop Corrections to Lamb Shift in Muonium and Positronium

Abstract

We calculate hard spin-independent three-loop radiative corrections to energy levels in muonium and positronium which are due to radiative insertions in two-photon exchange diagrams. These corrections could be relevant for the new generation of precise $1S-2S$ and $2S-2P$ measurements in muonium and positronium.

Comments: 14 pages, 6 figures; v.2: Title and abstract changed, new results included, list of references amended