ORDER ALPHA-4IN-ALPHA-1FRYD CORRECTIONS TO THE N = 1 AND N = 2 ENERGY-LEVELS OF POSITRONIUM

The order alpha-4 ln-alpha-1 f(RYD) corrections to the n = 1 and n = 2 energy levels of positronium are calculated using the conventional Bethe-Salpeter formalism. The Barbieri-Remiddi potential provides a suitable zeroth-order kernel about which perturbation theory is developed. A simple algorithmic method which amounts to an expansion of the interaction kernel in powers of the momentum divided by the mass is shown to suffice to extract the ln-alpha-1 terms from most of the interaction terms.