ReseaRch Quality assuRance foR the futuRe a ... - Lund University

Panel 13 – PHYSICS / MATHEMATICS
are needed. It is therefore a wise decision to keep the research activity in
Nuclear Structure Theory at Lund University at a good level, to keep its
international position. The age profile of the group is such that a few new
positions are clearly needed in the coming years. The overall rating of this
group lies between very good and excellent, tilting towards excellent.
2.4.2 Research
The main research effort of the group is oriented towards nuclei at their
extremes, i.e. extreme values of angular momentum or isospin. At high
values of angular momenta – rapidly rotating nuclei – the nuclear shape
may be very different from the ground state. For example, the shape may
become superdeformed (long axis to short axis ratio is 2:1) or triaxial (all
three nuclear axes having different sizes), with correspondingly special
modes of rotation. Due to the finite number of nucleons rotational bands
may terminate at some high angular momentum value. At high values of
isospin, i.e. very different numbers of neutrons and protons as compared
to stable nuclei along the beta-stability line, the nucleons may be weakly
bound, and unique quantum phenomena can be studied. In another research
project special effects from chaos in the nucleus are studied. Large
parts of the research are traditionally carried out in close collaboration
with experimental groups in Lund and around the world.
The group has been instrumental in showing that some observed bands
have triaxial superdeformation. In other studies some different features
of these bands were discussed, while the interpretation of bands of this
kind recently discovered in 157,158Er was described as ’a new class of
many-body symmetries describing nuclei at the phase transitional region’.
Other highlights include the study of superdeformed and terminating
bands with a close collaboration with the experimental nuclear structure
group at Lund University and the development of a theoretical model
which exhibits degenerate so called chiral bands, which is a manifestation
of dynamical spontaneous symmetry breaking.
Another important work is the investigation of a possible chaotic component
in nuclear masses which might be one reason why it has so far been
impossible to get a global description of nuclear masses with a mean error
smaller than 0.6 MeV. Using tools from semiclassical physics, a periodic
orbit theory could be developed to describe fluctuations of the BCS
pairing gap in nuclei as well as in other finite many-body systems, where
the chaos/order dynamics was found to be important.
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