Nuclear structure theory for RIA

MANIFESTO

Nuclear structure theory will progress by deriving its basic elements from the low-energy QCD theory and by constructing the best nucleon forces, energy-density functionals, and shell-model interactions to obtain unified and consistent description of phenomena and nuclides across the nuclear chart.

Atomic nuclei are aggregates of protons and neutrons bound together by strong interactions. They represent unique quantum self-bound systems with multitude of phenomena and properties that have been fascinating nuclear physicists since decades. Nuclear binding originates in the fundamental theory of Quantum Chromodynamics whereby quarks and gluons interact via color forces. One of the primary goals of the contemporary nuclear structure physics is to understand the links with this fundamental theory and to derive as many of nuclear properties by ab initio references to QCD. This is by no means an easy task, however, to our advantage stands significant separation of scales between the QCD (1000 MeV scale), pion mass (100 MeV scale), one-nucleon binding (10 MeV scale), and nuclear collective states (1 MeV scale). Using this gift of nature, we may attempt to use modern effective field theories to incorporate high-energy phenomena stemming from the high-energy scales into low-energy nuclear structure physics.

There are only less than 300 stable nuclides in nature, while already about 3000 other ones have been synthesized and studied in nuclear structure laboratories. However, the nuclear landscape extends further away into uncharted territories, where probably double of that await discovery. Properties of these exotic systems cannot be at present reliably derived from theoretical models, because our knowledge of basic ingredients thereof is still quite rudimentary. Derivations form first principles allow us already now to recognize general features of nuclear forces, energy-density functionals, or shell-model interactions, however, plenty of these features require careful adjustment to precise nuclear data. Such adjustments, especially when performed for exotic, extreme systems, provide invaluable information, and then in turn allow for more reliable extrapolations. A unified and consistent approach to nuclear structure phenomena described within guiding principles of low-energy QCD and many-body theories will be the main line of investigation in the years to come.

Nuclei at the extremes of the nuclear chart, which will be abundantly produced by RIA, are now at the focus of the nuclear structure theory, because they magnify principal uncertainties of the theoretical description and best allow us to make improvements. Nuclei near neutron drip line give us unique opportunity to study very asymmetric nuclear matter, or even pure neutron matter in the skin region. Their weak binding and low density of matter are trademarks of systems that nowhere else can be produced in the laboratory. Special features like halo phenomena, Borromean binding, coupling to unbound states, or cluster formation require developing novel theoretical methods. Superheavy nuclei attract tremendous public attention due to the possibility of creating new elements, but they also provide invaluable tests of theory when it is ported to extremal masses and nuclear shells, and requires very far reaching extrapolations. Proton rich nuclei offer possibilities of extrapolations to systems obeying unusual features of pairing, isospin symmetry, and proton, two-proton, or cluster emissions.

Abundant production of exotic nuclei will also allow us to study unusual nuclear shapes and currents, which may appear only at special, often very exotic combinations of proton and neutron numbers. This will offer new input to theories of collective motion as rooted in the fundamental shell-model and/or mean-field pictures of nuclei. Spectroscopy of exotic systems will be an invaluable source of information to learn more about up to now poorly known channels of the shell-model interactions and energy-density functionals. Investigations of rotational states, together with studying new spontaneous symmetry breaking effects, will give us access to spin-spin and spin-isospin channels of interactions, and will allow us to better know shell properties of nuclei. Fission phenomena will be studied within theories based directly on nuclear interactions, which will better identify the role of correlations in large many-fermion systems. Study of dynamical symmetries in model spaces will allow for better a understending of simple phenomena in these unbelievably complicated systems

Nuclear structure theory is a twin brother of theories of nuclear reactions and nuclear astrophysics. On the one hand it provides input to these theories, but on the other hand, it takes abundantly from the results. In particular, studies of structure through nuclear reactions on exotic systems will certainly be the main source of information about them. Numerous links between the three subdomains make them into a unity, and specific specializations are required only by the fantastic richness of the domain.