Abstract

Positronium (Ps)¹ is one of the most fundamental systems available for precision studies. It provides a unique opportunity for studying a purely leptonic two-body system with virtual annihilation interactions and the quantum electrodynamic (QED) corrections to that system. The Dirac equation provides an adequate starting point for the description of hydrogen, hydrogenlike ions, and muonium but cannot be used to describe Ps. There are fully covariant formulations of the two-body problem, such as the Bethe-Sal- peter equation, but there is no known analytic solution. Recent advances in treating the two-body problem have been made,² and further work will doubtlessly be spurred on by experimental progress in Ps and quarkonium spectroscopy.

© 1984 Optical Society of America