889 research outputs found
Optimizing phonon space in the phonon-coupling model
We present a new scheme to select the most relevant phonons in the
phonon-coupling model, named here time-blocking approximation (TBA). The new
criterion, based on the phonon-nucleon coupling strengths rather than on
values, is more selective and thus produces much smaller phonon spaces
in TBA. This is beneficial in two respects: first, it curbs down the
computational cost, and second, it reduces the danger of double counting in the
expansion basis of TBA. We use here TBA in a form where the coupling strength
is regularized to keep the given Hartree-Fock ground state stable. The scheme
is implemented in an RPA and TBA code based on the Skyrme energy functional. We
first explore carefully the cutoff dependence with the new criterion and can
work out a natural (optimal) cutoff parameter. Then we use the freshly
developed and tested scheme to a survey of giant resonances and low-lying
collective states in six doubly magic nuclei looking also on the dependence of
the results when varying the Skyrme parametrization.Comment: 9 figures, 3 table
Self-consistency in the phonon space of the particle-phonon coupling model
In the paper the non-linear generalization of the time blocking approximation
(TBA) is presented. The TBA is one of the versions of the extended random-phase
approximation (RPA) developed within the Green-function method and the
particle-phonon coupling model. In the generalized version of the TBA the
self-consistency principle is extended onto the phonon space of the model. The
numerical examples show that this non-linear version of the TBA leads to the
convergence of the results with respect to enlarging the phonon space of the
model.Comment: 12 pages, 10 figures, 1 tabl
Final state interactions and correlations: are the latter observable?
Are effects of short range correlations in the ground state of the target
nucleus (initial state correlations ISC) observable in experiments on
quasielastic scattering at large missing momentum ? Will the
missing momentum spectrum observed at CEBAF be overwhelmed by final state
interactions (FSI) of the struck proton? The recent advances in the theory of
FSI and findings of complex interplay and strong quantum-mechanical
interference of FSI and ISC contributions to scattering at p_{m}\gsim
1\,fm are reviewed. We conclude that for p_m \gsim 1 \, fm
quasielastic scattering is dominated by FSI effects and the sensitivity to
details of the nuclear ground state is lost.Comment: Invited Talk given by N.N.Nikolaev at the Conference on Perspectives
in Nuclear Physics at Intermediate Energies (Trieste, Italy, May 1995) 18
pages, uuencoded including all figure
Landau-Migdal vs. Skyrme
The magnitude and density-dependence of the non-spin dependent Landau-Migdal
parameters are derived from Skyrme energy functionals and compared with the
phenomenological ones. We perform RPA calculations with various approximations
for the Landau-Migdal particle-hole interaction and compare them with the
results obtained with the full Skyrme interaction. For the first time the next
to leading order in the Landau-Migdal approach is considered in nuclear
structure calculations.Comment: Dedicated to the memory of G.E. Brow
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