Theory of antihydrogen atoms.

Our world is made of matter. Its building stones are atoms. Atoms in turn are made of particles: protons, neutrons, and electrons. For every particle there is a mirror image - an antiparticle. The charge and magnetic moment of an antiparticle is opposite that of an ordinary particle, but otherwise they are, as far as we know, the same. Just as particles build up matter, antimatter can be built by antiparticles. But antiparticles do not exists naturally, they will sooner or later annihilate when they meet ordinary matter.The simplest antiatom, antihydrogen, has recently been created in two experiments, ATHENA and ATRAP, at CERN. The goal of these experiment is to store antihydrogen in an atom trap, so that its detailed properties can be studied. Although antimatter is believed to be a perfect mirror image of matter, this is only known to be true within a certain precision. If any small flaw could be found in the mirror image, this would have profound consequences for our understanding of fundamental physics and cosmology. Perhaps it could explain a very obvious asymmetry between matter and antimatter; we only see matter around us.This project aims to advance the theoretical understanding of antihydrogen, in order to support the experiments. The antihydrogen atoms formed so far cannot be used for detailed studies. One reason is that the atoms are just barely bound together. In order to make measurements they need to be brought to their most tightly bound state: their quantum mechanical ground state. Another reason is that the antiatoms are too hot. Methods have to be found to either cool them, or to form them directly at lower temperatures. These are problems I intend to address using quantum mechanical calculations.I will also study the interaction between matter and antimatter. In a single atom-antiatom collision annihilation is only one of several possible outcomes. The atom and antiatom may also bounce apart again without annihilating, or new systems may be formed, e.g. nucleus-antinucleus and electron-antielectron. Even an atom-antiatom molecule could be formed, although with a very limited lifetime. Atom-antiatom collisions are in many ways different, and more difficult to calculate, than collisions between ordinary atoms. A completely new feature is the strong nuclear force, which causes annihilation, but also has an influence on other processes. Another difference is that the nucleus and antinucleus have opposite electric charge, which means that they attract each other, contrary to ordinary nuclei which never approach close to each other in collisions. Therefore many concepts from traditional atomic physics are changed, and new theoretical methods must be developed.The research will be undertaken at the University of Wales, Swansea. Here I will work together with the experimental group of Prof. Michael Charlton. This group was part of the ATHENA collaboration which first produced cold antihydrogen, and is now part of ATHENA:s successor ALPHA.