2,019 research outputs found
Coordinate representation for non Hermitian position and momentum operators
In this paper we undertake an analysis of the eigenstates of two non
self-adjoint operators and similar, in a suitable sense, to
the self-adjoint position and momentum operators and
usually adopted in ordinary quantum mechanics. In particular we discuss
conditions for these eigenstates to be {\em biorthogonal distributions}, and we
discuss few of their properties. We illustrate our results with two examples,
one in which the similarity map between the self-adjoint and the non
self-adjoint is bounded, with bounded inverse, and the other in which this is
not true. We also briefly propose an alternative strategy to deal with
and , based on the so-called {\em quasi *-algebras}.Comment: Accepted in Proceedings of the Royal Society
Pairing and realistic shell-model interactions
This paper starts with a brief historical overview of pairing in nuclei,
which fulfills the purpose of properly framing the main subject. This concerns
the pairing properties of a realistic shell-model effective interaction which
has proved very successful in describing nuclei around doubly magic 132Sn. We
focus attention on the two nuclei 134Te and 134Sn with two valence protons and
neutrons, respectively. Our study brings out the key role of one particle-one
hole excitations in producing a significant difference between proton and
neutron pairing in this region
Shell-model studies on exotic nuclei around 132Sn
The study of exotic nuclei around 132Sn is a subject of current experimental
and theoretical interest. Experimental information for nuclei in the vicinity
of 132Sn, which have been long inaccessible to spectroscopic studies, is now
available thanks to new advanced facilities and techniques. The experimental
data which have been now become available for these neutron-rich nuclei may
suggest a modification in the shell structure. They are, in fact, somewhat
different from what one might expect by extrapolating the existing results for
N<82, and as a possible explanation a change in the single-proton level scheme
has been suggested. The latter would be caused by a more diffuse nuclear
surface, and could be seen as a precursor of major effects which should show up
at larger neutron excess. New data offer therefore the opportunity to test the
shell model and look for a possible evolution of shell structure when going
toward neutron drip line. This is stimulating shell-model studies in this
region. Here, we present an overview of recent shell-model studies of 132Sn
neighbors, focusing attention on those calculations employing realistic
effective interactions.Comment: 8 pages, 4 tables, invited talk at INPC2007, Tokyo, Japan, June 3-8
2007. To be published in Nuclear Physics
Shell-model study of quadrupole collectivity in light tin isotopes
A realistic shell-model study is performed for neutron-deficient tin isotopes
up to mass A=108. All shell-model ingredients, namely two-body matrix elements,
single-particle energies, and effective charges for electric quadrupole
transition operators, have been calculated by way of the many-body perturbation
theory, starting from a low-momentum interaction derived from the
high-precision CD-Bonn free nucleon-nucleon potential. The focus has been put
on the enhanced quadrupole collectivity of these nuclei, which is testified by
the observed large B(E2;0+ -> 2+)s. Our results evidence the crucial role
played by the Z=50 cross-shell excitations that need to be taken into account
explicitly to obtain a satisfactory theoretical description of light tin
isotopes. We find also that a relevant contribution comes from the calculated
neutron effective charges, whose magnitudes exceed the standard empirical
values. An original double-step procedure has been introduced to reduce
effectively the model space in order to overcome the computational problem.Comment: 6 pages, 6 figures, 2 table
p-Shell Nuclei and Two-Frequency Shell Model with a Realistic Effective Interaction
We have studied p-shell nuclei using a two-frequency shell-model approach
with an effective interaction derived from the Bonn-A nucleon-nucleon potential
by means of a G-matrix folded-diagram method. First, we briefly describe our
derivation of the effective interaction in a model space composed of harmonic
hoscillator wave functions with two different length parameters, b_in and
b_out, for the core and the valence orbits, respectively. Then we present some
selected results of our calculations. We show that a good agreement with
experiment is obtained, which is definitely better than that provided by a
standard one-frequency calculation. A comparison with results obtained from
large-basis shell-model calculations is also made.Comment: 9 pages, 1 figure, talk presented at VIII Convegno di Fisica Nucleare
Teorica, Cortona, 18-21 Ottobre 200
Low-momentum Nucleon-Nucleon Potential and Hartree-Fock Calculations
A low-momentum nucleon-nucleon (NN) potential V-low-k is derived from modern
realistic NN potentials by integrating out the high-momentum modes. The smooth
V-low-k may be used as input for nuclear structure calculations instead of the
usual Brueckner G matrix. Such an approach eliminates the energy dependence one
finds in the G-matrix approach, allowing this interaction to be used directly
in Hartree-Fock calculations. Bulk properties of 16O have been calculated
starting from different NN potentials. Our results, obtained including up to
second order contributions in the Goldstone expansion, are in good agreement
with experiment.Comment: 7 pages, talk presented at IX Convegno su Problemi di Fisica Nucleare
Teorica, Cortona (Italy), October 9-12 200
Shell-Model Calculations with Realistic Effective Interactions
In this paper, we present some results of shell-model calculations employing
effective interactions derived from the CD-Bonn free nucleon-nucleon potential.
These concern 18O, 134Te, and 210Po, and are part of a comprehensive study of
nuclei around doubly closed shells. Comparison of the calculated results with
experimental data illustrates the degree of accuracy of modern realistic
shell-model calculations.Comment: Talk presented at INPC 2001, 29 July - 3 August 2001, Berkeley (USA
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