Perspectives of Nuclear Physics in Europe - European Science ...

Each of these extensions will open the possibilities of
new phase transitions.
New results are also expected from the microscopic
approaches based on EDF methods. These should allow
a deeper understanding of the origin and the nature of
the nuclear shape phase transitions. In particular, the
richer scenario offered by these microscopic approaches
with respect to more schematic boson models will lead
to more realistic predictions for the position of the critical
nuclei in the mass table
Reactions
The availability of low- and high-energy radioactive
beams and, in particular the discovery of halo-nuclei,
has brought out a renewed interest in the modeling of
nuclear reactions. To take into account the complexity
of the many-body problem, current approaches to
reaction theory involve different approximations whose
validity needs to be checked, in particular when applied
to exotic light nuclei.
In the last few years important advances include:
(a) the description of very-low energy subbarrier fusion
processes that should provide information on the
inner part of the ion-ion potential;
(b) general parameterizations of the ion-ion optical
potentials aimed at the description of both fusion
and quasielastic processes for stable and unstable
systems;
(c) a consistent coupled-channel microscopic formalism
for the description of multinucleon transfer reactions,
with the intent of clarifying the smooth transition from
grazing to deep-inelastic processes;
(d) massive calculations of elastic and break-up
processes involving exotic halo nuclei, exploiting
coupled-channels approaches based on continuum
discretization;
(e) novel approaches based on the ab initio inclusion of
the halo few-body nature into the reaction formalism;
(f) extensions to the explicit treatment of four-body channels
(as in break-up reactions involving two-neutron
halo nuclei).
Perspectives
There are two major issues in any reaction approach:
first, to ensure that sufficiently detailed microscopic
structure information of the interacting nuclei is incorporated
(via optical potentials, form-factors, spectroscopic
factors, etc.) and, second, a proper treatment of the
relevant dynamics. These two aspects are often intertwined
and need to be carefully addressed.
Within this general framework several topics can be
singled out for future work. In particular:
(a) a more extended use of microscopic models for the
excitation (via different probes as Coulomb, inelastic,
charge-exchange, transfer, etc) of different collective
and non-collective modes (e.g. dipole pigmy
states).
(b) a consistent description of the interplay between
continuum and many-body correlations, for systems
with unbound ground states and above threshold for
weakly-bound systems
(c) a further clarification of the reaction mechanism for
two- and multiparticle transfer reactions, in relation
with the role of pairing-like interactions (in both isospin
T=0 and T=1 channels)
(d) a systematic comparison between different scattering
approaches with similar structure and dynamical
inputs, in order to clarify the validity of different
approximation schemes
(e) the development of a reliable framework for the study
of quasi-free breakup, that will yield information on
the wave function of the struck particle, in particular
at high energies at which the scattering framework
is expected to become simpler.
In addition to developments within the conventional
models, promising results have been obtained employing
other approaches, in some cases novel, and in other
cases revitalized after decades of obsolescence (such
as TDHF mean-field calculations for reactions). In the
case of reactions involving light ions, in particular, much
is expected from the extension of ab initio shell-model
calculations to reactions, as well as from structure models
based on the cluster approach.
Toward a unified description
of nuclear structure and reactions
Nuclear theory is rapidly evolving from studies of nuclei
close to the valley of beta-stability towards a description
of vast regions of short-lived and exotic nuclei far from
stability and at the nucleon drip-lines. Such an expansion
imposes stringent constraints on microscopic structure
and reaction models that are being developed. These
mainly concern the model space that must take into
account the coupling between bound states and the
continuum, and the construction of effective interactions
that can be used all over the nuclear chart. This
overview of the various aspects of modern nuclear theory
has focused on the current status and perspectives of
our understanding and modelling of low-energy nuclear
physics.
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