Positron Annihilation and Positronium Formation : A Unified Theory in Terms of a Complex Potential

Abstract

In a positron-atom encounter, electron-positron (e^- e⁺) pair annihilation may occur as well as the formation of a bound system e^- e⁺ called positronium. In the conventional theory, they have been treated as two independent processes. This theory is known, however, to break down in certain positron-energy regions, where it leads to an unphysical divergence of the annihilation cross section. We propose a new, more rigorous unified theory that deals with these two processes on the same footing, using a complex, absorption potential. This new theory tells that the two "processes" are in fact inseparable two pathways or mechanisms leading to the same final channel of pair annihilation. Applications to positron collisions with hydrogen atoms are also discussed.