P. Navratil

Nuclear Structure from First Principles: Ab Initio No-Core Shell Model for Light Nuclei

In recent years, construction of accurate nucleon-nucleon potentials and increases in computing power have led to new methods capable of solving the nuclear structure problem for systems of more than four nucleons. In these lectures I will describe one of these methods, the ab initio no-core shell model (NCSM). The principal foundation of this approach is the use of effective interactions appropriate for the large, but finite, harmonic-oscillator basis employed in the calculations. These effective interactions are derived from the underlying realistic inter-nucleon potentials in a way that guarantees convergence to the exact solution as the basis size increases.
I will discuss convergence tests of the method and nuclear structure results for light nuclei obtained by using several modern nucleon-nucleon potentials, including those derived from the effective field theory.
At present, the ab initio NCSM is capable of including the much-less-explored realistic three-nucleon forces. An important result of these nuclear-structure studies is the significance of three-nucleon interaction in determining not only the binding energy, but also the excitation spectra and other observables. Consequently, nuclear-structure calculations are becoming a tool in discriminating different three-body interaction models and at the same time can put constraints on the three-body force parameters.
It is a challenging task to extend ab initio nuclear structure approaches to the description of nuclear reactions. For the NCSM, this is in particular true concerning the low-energy reactions relevant for astrophysics. The first step toward this goal is the cluster decomposition of the NCSM eigenstates. I will present results of cluster form factor calculations for light p-shell nuclei, e.g. 7Li->3H+4He, 6Li->4He+d etc. Concerning the direct reactions, a possible answer is the application of semi-microscopic folding approaches to construct optical potentials from nuclear densities obtained in the NCSM. I will describe calculations performed to interpret the new CNS 6He+p experiment with a polarized proton target.