Over the last 15 years our research group has been developing a first principles approach for calculating the properties of atomic nuclei, starting from the fundamental interactions among the protons and neutrons, both pairwise and in terms of triplets. The key to the successes of this approach is the treatment of all the protons and neutrons in the nucleus as being active, instead of holding some of them static, that is, as an inert core. Hence, the name of our approach, the No Core Shell Model. By treating all particles active, we are able to calculate exactly the medium-modified interaction among particles inside the nucleus and, thereby, the details of the nuclear structure produced by these interactions.
Besides giving us microscopic results for the theoretical properties of atomic nuclei, our formalism allows us to analyze different theoretical models for the interactions among three particles, the so-called three nucleon interaction. Understanding the nature of the three-nucleon interaction is one of the most fundamental problems in theoretical nuclear physics at this time. This formalism can also be used for investigating three-particle interactions in other physical systems. In order to perform our large-scale no-core shell-model calculations, we have developed several new shell-model computer codes, which can handle up to one-billion single-particle basis states. Again such computer codes have applications to the solving of important, outstanding problems in other fields of research, such as in condensed matter physics and in chemistry. Our research problem has also played a significant role in educating and training a new generation of young nuclear-structure theorists. During the course of our current research program on the no-core shell model, we have educated five new PhD nuclear theorists and trained and mentored six postdoctoral research associates at the University of Arizona. Several more graduate students and postdoctoral research associates have been involved our collaborations with other nuclear-theory groups in the USA, Europe, Australia, and Tunisia.
