Hard spin-independent three-loop radiative contributions to energy levels in positronium generated by the two-photon-exchange diagrams with one-loop insertions fermion lines and exchanged photons are calculated. This is a next step calculations of all corrections order mα7 inspired new generation precise 1S−2S 2S−2P measurements positronium.

We consider the problem of the scattering of a photon by hydrogen in the ground state when the photon has its principal frequencies near that of Lyman-rv radiation. We obtain the scattering operator and cross-section for this process. Our procedure is to adapt Dirac's theory of resonance scattering to the problem and, by quantizing the electromagnetic field in an angular momentum basis, to solv...

We compute trace anomaly contribution to hydrogen atom mass, which turns out be related the part of Lamb shift. To best our knowledge, this is a first model independent calculation bound state. This finding might shed new light on understandings mass structure QCD states, such as, heavy quarkonium.

A source of narrow bandwidth (,800 MHz) tunable laser radiation at 58.4 nm has been developed and is applied to record the 11S-21P transition in He and He. From the He transition frequency of 171 134.8936s58d cm21 a fivefold improved ground state Lamb shift of 1.3763s58d cm21 is deduced, in good agreement with the theoretical value of 1.3755s10d cm21. The measured 11S-21P transition isotope shi...