New Directions in Nuclear Structure Theory

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Research Program: One of the fundamental outstanding problems in the field of physics is to understand the structure and properties of the atomic nucleus starting from the basic interactions among the neutrons and protons (collectively called nucleons) and employing only quantum mechanical many-body theory. Great progress has been made in solving this problem in the last ten years due to new developments in nuclear many-body theory and advances in computer technology. One of these developments is the so-called No Core Shell Model (NCSM), in which all the nucleons in a nucleus are treated as being active, instead of only a few valence nucleons outside an assumed inert core. The NCSM approach simplifies the structure of the many-body problem to be solved and has had considerable success in describing the properties of light nuclei, up to masses near oxygen, i.e., nucleon number 16. This same NCSM approach can be and is being now applied to nuclear reaction theory. One of the fundamental advances following from these investigations is the understanding of the importance of not only pair-wise interactions among nucleons in determining nuclear structure, but also of triplet (or three-nucleon) interactions. More work needs to be done to determine whether or not four-nucleon and higher-nucleon interactions are also necessary. Another important problem is to understand the relationship between the energy required in the two-nucleon system relative to the energy available for all the nucleons in a nucleus.Broader Impact: Our NCSM approach not only has wide applications in theoretical nuclear physics but also in atomic and molecular physics and in condensed matter physics, such as, the problem of a small number of fermions, e.g., electrons, constrained by an harmonic oscillator trap. In addition, our research program is actively educating and mentoring a new generation of young nuclear theorists. For example, during the previous award period, our research group included two undergraduate students, two graduate students, and three post-doctoral research associates. The principal investigator also teaches undergraduate and graduate nuclear physics courses at the University of Arizona and lectures on nuclear structure theory at international summer schools, workshops and symposia.