Corrections from the Breit interaction to basic properties of atomic Cs are determined in the framework of third-order relativistic many-body perturbation theory. The corrections to energies, hyperfine-structure constants, off-diagonal hyperfine 6S-7S amplitude, and electric-dipole matrix elements are tabulated. It is demonstrated that the Breit corrections to correlations are comparable to the...

The exclusive production of one μ+μ− pair in collisions of two ultra-relativistic nuclei is considered. We present the simple method for calculation of the Born cross section for this process. Then we found that the Coulomb corrections to this cross section (which correspond to multi-photon exchange of the produced μ with nuclei) are small while the unitarity corrections are large. This is in s...

We describe a simplified derivation for the relativistic corrections of order α 4 for a bound system consisting of two spinless particles. We devote special attention to pionium, the bound system of two oppositely charged pions. The leading quantum electrodynamic (QED) correction to the energy levels is of the order of α 3 and due to electronic vacuum polarization. We analyze further correction...