QED theory of the spectral line profile and its applications to atoms and ions

A review of the current status of the theoretical study of spectral line profile for systems with few electrons is given in this paper. The hydrogen atom and highly charged ions are presented in this work. In particular, the line profiles for cascade processes, the asymmetry of the line profile beyond the resonance approximation and the overlap of the resonances are investigated. The line profile approach is introduced for the investigation of the energy levels and the transition probabilities for bound electrons within the framework of quantum electrodynamics. The energies and transition probabilities for few-electron systems are evaluated. The line profile approach is also applied to the case of the quasidegenerate levels in highly charged ions.