# Quantum-Mechanical Many-Body Theory

Efforts in this cross-disciplinary area have the goal of microscopic, or *ab initio* prediction of measurable properties of strongly interacting quantum systems. Attention is directed primarily to real physical systems under realistic conditions of interactions, density, and temperature, rather than to idealized model problems.

The systems being considered span a broad range, from nuclei, neutron-star matter, and hypernuclear matter, to Bose and Fermi superfluid helium liquids, to strongly interacting electron systems and Hamiltonian lattice-gauge problems. The strong correlations present in these systems render traditional mean field descriptions inadequate. Accordingly, we are applying and further developing two of the most powerful and accurate semi-analytic theoretical approaches currently available: the method of correlated basis functions (CBF) and self-consistent Green's function theory (SCGF). Both approaches have been largely developed at Washington University. While thay are both comprehensive and in principle exact, they have complimentary strengths.

In combination, the two methods provide efficient means for attacking problems of fundamental and topical interest in nuclear physics, astrophysics, low-temperature physics, condensed-matter physics, and particle physics.

Professor Clark, working with collaborators and students, is currently using CBF theory and other methods of microscopic analysis to uncover new aspects of Bose-Einstein condensation in liquid ^{4}He and fermion pairing phenomena in neutron-star matter and other nuclear systems.

Professor Dickhoff and his students apply Green's function methods to the solution of a variety of many-particle problems. Important experimental developments in the last 10 years involving the scattering of high-energy electrons off nuclei have been accompanied by a similarly successful increase in the theoretical description of the nucleus.

Professor Dickhoff's group has made pivotal contributions to the current understanding of those properties of the nucleus which are elucidated by the simultaneous detection of the scattered electron together with one proton which is removed from the nucleus in the scattering process.