Relativistic calculation of the 2 (1)S0-2 (1),3P1 transitions in berylliumlike molybdenum and berylliumlike iron

Ab initio Calculations of Energy Levels in Be-Like Xenon: Strong Interference between Electron-Correlation and QED Effects

The strong mixing of close levels with two valence electrons in Be-like xenon greatly complicates ab initio QED calculations beyond the first-order approximation. Because of a strong interplay between the electron-electron correlation and QED effects, the standard single-level perturbative QED approach may fail, even if it takes into account the second-order screened QED diagrams. In the present Letter, the corresponding obstacles are overcome by working out the QED perturbation theory for quasidegenerate states. The contributions of all the Feynman diagrams up to the second order are taken into account. The many-electron QED effects are rigorously evaluated in the framework of the extended Furry picture to all orders in the nuclear-strength parameter αZ. The higher-order electron-correlation effects are considered within the Breit approximation. The nuclear recoil effect is accounted for as well. The developed approach is applied to high-precision QED calculations of the ground and singly excited energy levels in Be-like xenon. The most accurate theoretical predictions for the binding and excitation energies are obtained. These results deviate from the most precise experimental value by 3σ but perfectly agree with a more recent measurement.

QED effects in Cu-like Pb recombination resonances near threshold

In an electron-ion recombination study with Pb53+ dielectronic recombination resonances are found for as low as approximately 10(-3)-10(-4) eV relative energy. The resonances have been calculated by relativistic many-body perturbation theory and through comparison with experiment the Pb53+(4p(1/2)-4s(1/2)) energy splitting of approximately 118 eV is determined with an accuracy comparable to the position of the first few resonances, i.e., approximately 10(-3) eV. Such a precision provides a test of QED in a many-body environment at a level which can still not be reached in calculations.