Many-body theory of positron-atom interactions

The interaction of low-energy positrons with atoms is characterised by strong electron-positron correlation effects. For example, they increase the positron annihilation rate in collisions with Xe atoms by three orders of magnitude! We have developed a many-body theory approach [1] which accounts for all major correlation effects, i.e, polarization of the atom by the positron, virtual positronium formation, and short-range enhancement of the electron-positron contact density. The first two give rise to strong positron-atom attraction. It affects positron elastic scattering and promotes positron-atom binding. The third effect determines positron-atom annihilation rates and spectra of annihilation gamma quanta [2]. Thus, a good quantitative understanding of positron-atom interactions has been achieved. This gives hope of understanding a much more difficult problem of positron annihilation with polyatomic molecules, where molecular vibrational degrees of freedom play an important role [3,4]. \begin{enumerate}\setlength{\itemsep}{-3pt}\setlength{\itemindent}{-12pt} \item G. F. Gribakin and J. Ludlow, Phys. Rev. A {\bf 70}, 032720 (2004). \item L. J. M. Dunlop and G. F. Gribakin, submitted to J. Phys. B (2005). \item C. M. Surko, G. F. Gribakin and S. J. Buckman, J. Phys. B {\bf 38}, R57 (2005). \item G. F. Gribakin and P. M. W. Gill, Nucl. Instrum. and Methods B {\bf 221}, 30 (2004). \end{enumerate}