Primary research areas have been quantum electrodynamics, elementary particles and scattering theory, the latter with an emphasis on three-body problems with applications in atomic physics.

The three-body problem is famous in both classical and quantum mechanics, but my research has concentrated on the quantum case. In recent years I have been interested in an anomalous situation with regard to so-called "capture" reactions, in which an energetic projectile captures a particle from a composite target, e.g., A + (BC) -> (AB) + C, and "break-up" (or in the atomic case, ionization): A + (BC) -> A + B + C. An example of capture from atomic physics would be a proton projectile capturing an electron from a target atom, emerging as a neutral hydrogen atom. In ionization all three particles would be free. These processes are very fundamental, and experiments studying them are done in many laboratories around the world. Unfortunately, the theory, even when pure Coulomb potentials are used (especially when pure Coulomb potentials are used!), proves to be extremely difficult and many approximate techniques have been developed. Recently, I have discovered that for certain masses of the three particles, capture is kinematically forbidden by means of the simplest double collision process. I am currently studying the possibility of capture by means of triple collisions when the masses lie in these regions. Together, with a graduate student we have shown that capture by a triple-collision process is indeed possible when double collision capture is not. We are now studying the implications of this for the quantum mechanical properties of the three particle system.

In the case of breakup reactions involving three charged particles in the final state, such as ionization of an atom by electron collision, calculations require accurate approximate wave functions, since no exact ones exist. Important contributions come from situations where one pair of particles emerges with nearly the same velocity. I have recently published an improved wavefunction which is valid in this region, and which goes smoothly into the wavefunction valid when all three particle are moving apart. Numerical calculations of the ionization probability and angular distribution of the ionization products, using this improved wavefunction are in progress, as well as further improvements to the wavefunction.