For example, we plan to bring together shell-model theorists with researchers doing symplectic and cluster calculations to look for ways to accommodate these into a more comprehensive theory, i.e., how does collective rotational motion and clustering emerge in shell-model calculations. Theorists using group theory and cluster techniques will be brought into these discussions to study whether it is possible to to propose truncation schemes of the shell model based on symmetries and also to explore new methods to use group-theoretical techniques to model the nuclear many-body problem.

Another topic for extended discussion will be the role of the continuum in weakly-bound systems. This is of particular relevance in nuclei away from the stability line where all states are close to the neutron or proton separation threshold and effects of the continuum may play a crucial role in the phenomena, such as two-proton radioactivity. And again, the role of special symmetries in the treatment of "open" quantum systems needs to be investigated, in particular with regard to relevant non-compact group structures.

A further focus will be on fostering exchanges among many-body theorists working on symplectic methods, the coupled-cluster approach, the Green function formalism, Monte Carlo methods, and unitary transformations of nuclear operators to investigate new ways to apply their schemes and build them into a more comprehensive many-body theory, e.g., through multiple unitary transformations or multiple effective model-space Hamiltonians.

And, since through Effective Field Theory (EFT) it is now possible to link QCD physics directly to shell-model effective interactions and other physical operators in a truncated model space, ways to pursue and further develop this connection will be another major topic of our program.

The program would address the following issues, among others:

1. Potentials:

• The nature of the NN potential: CPT potentials vs empirical potentials.

• Three-nucleon interactions, particularly those based on CPT.

• The application of these NN and NNN potentials to nuclear-structure calculations.

• Evidence for or against the need for higher-rank potentials, and, in particular, the possible importance of NNNN correlations in nuclei.

• The modification of these potentials inside the nuclear medium, i.e., what is the structure of the renormalized or effective interaction needed for nuclear-structure calculations, particularly for heavier nuclei?

• Linkages among QCD, lattice gauge calculations, EFT/CPT and nuclear structure calculations.

• Consistent treatment of regulators/cutoffs between the 2/3-body systems and the many-body systems.

• The structure of other effective operators, such as the radius, the quadrupole moment, etc.

• Development of new many-body approaches for including more NN correlations in small model spaces.

• Combining shell-model, cluster and group-theory techniques into an unified approach to nuclear-structure calculations.

• How to combine the bound and weakly-bound nuclear regimes: merging of standard nuclear shell-model methods and nuclear-reaction technology. Discussion of the different available approaches and the possible role of symmetries in their treatment.

• What scope of physics applications will be possible with the present and next generation of interactions/algorithms/computers?

• Benchmark comparisons of different many-body methods, as well as efficiency tests.

• Assessments of the rate of convergence of different numerical techniques for computing nuclear properties.