Many-body theory and calculations of positron scattering, binding and annihilation with atoms and polyatomic molecules*

Pioneering technological developments have enabled the routine trapping, accumulation and beam delivery of low-energy positrons for studies of fundamental atomic and molecular interactions, and the formation of positronium (Ps) and antihydrogen. The ability of positrons to annihilate with atomic and molecular electrons -- to release two characteristic and detectable gamma rays -- makes positrons and Ps unique probes of matter, and gives them important use across vast length scales, including as diagnositics of industrially important materials, in medical imaging (via PET, positron emission tomography), and in understanding the composition of the galaxy. 

Experiments with antimatter are costly and challenging. Their proper interpretation, and that of the positron-based material science techniques, and the development of next generation positron-based technologies (traps/beams/PET) relies on theoretical understanding of positron interactions with atoms, molecules and condensed matter. Their interactions are, however, characterised by strong correlations, e.g., polarization of the electron cloud and virtual-Ps formation, making their theoretical description a challenging many-body problem. 

I will discuss the many-body theory of positron interactions with atoms and polyatomic molecules, which recently gave the first ab initio verification of long-standing measurements of positron-molecule binding energies [1], and has since been developed to positron scattering and annihilation [2]. In doing so, I hope to convince you that positron physics remains fun [3].

[1] J. Horfierka, B. Cunningham, C. M. Rawlins, C. H. Patterson and D. G. Green, accepted to Nature (2022). 

[2] C. M. Rawlins, J. Horfierka, B. Cunningham, C. H. Patterson and D. G. Green, to be submitted (2022). 

[3] R. J. Drachman, "Why positron physics is fun", AIP Conference Proceedings 360, 369 (1996).