102 research outputs found
Factorization of shell-model ground-states
We present a new method that accurately approximates the shell-model
ground-state by products of suitable states. The optimal factors are determined
by a variational principle and result from the solution of rather
low-dimensional eigenvalue problems. The power of this method is demonstrated
by computations of ground-states and low-lying excitations in sd-shell and
pf-shell nuclei.Comment: 5+epsilon pages, 5 eps-figures. Main additions: wave-function
overlaps, angular momentum expectation values, application to Ni56. To be
published as Rapid Communication in PR
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Ab-initio Reaction Calculations for Carbon-12 (ESP Technical Report): ALCF-2 Early Science Program Technical Report
Report about the Ab-initio Reaction Calculations for Carbon-12 (ESP Technical Report): ALCF-2 Early Science Program Technical Repor
Many-body effects in 16O(e,e'p)
Effects of nucleon-nucleon correlations on exclusive reactions on
closed-shell nuclei leading to single-hole states are studied using
( MeV, ) as an example. The quasi-hole wave
function, calculated from the overlap of translationally invariant many-body
variational wave functions containing realistic spatial, spin and isospin
correlations, seems to describe the initial state of the struck proton
accurately inside the nucleus, however it is too large at the surface. The
effect of short-range correlations on the final state is found to be largely
cancelled by the increase in the transparency for the struck proton. It is
estimated that the values of the spectroscopic factors obtained with the DWIA
may increase by a few percent due to correlation effects in the final state.Comment: 21 Pages, PHY-7849-TH-9
Monte Carlo integration in Glauber model analysis of reactions of halo nuclei
Reaction and elastic differential cross sections are calculated for light
nuclei in the framework of the Glauber theory. The optical phase-shift function
is evaluated by Monte Carlo integration. This enables us to use the most
accurate wave functions and calculate the phase-shift functions without
approximation. Examples of proton nucleus (e.g. p-He, p-Li) and
nucleus-nucleus (e.g. HeC) scatterings illustrate the effectiveness
of the method. This approach gives us a possibility of a more stringent
analysis of the high-energy reactions of halo nuclei.Comment: 20 pages, 8 figure
Spin-orbit induced backflow in neutron matter with auxiliary field diffusion Monte Carlo
The energy per particle of zero-temperature neutron matter is investigated,
with particular emphasis on the role of the interaction. An
analysis of the importance of explicit spin--orbit correlations in the
description of the system is carried out by the auxiliary field diffusion Monte
Carlo method. The improved nodal structure of the guiding function, constructed
by explicitly considering these correlations, lowers the energy. The proposed
spin--backflow orbitals can conveniently be used also in Green's Function Monte
Carlo calculations of light nuclei.Comment: 4 pages, 1 figur
Momentum and Energy Distributions of Nucleons in Finite Nuclei due to Short-Range Correlations
The influence of short-range correlations on the momentum and energy
distribution of nucleons in nuclei is evaluated assuming a realistic
meson-exchange potential for the nucleon-nucleon interaction. Using the
Green-function approach the calculations are performed directly for the finite
nucleus O avoiding the local density approximation and its reference to
studies of infinite nuclear matter. The nucleon-nucleon correlations induced by
the short-range and tensor components of the interaction yield an enhancement
of the momentum distribution at high momenta as compared to the Hartree-Fock
description. These high-momentum components should be observed mainly in
nucleon knockout reactions like leaving the final nucleus in a state
of high excitation energy. Our analysis also demonstrates that non-negligible
contributions to the momentum distribution should be found in partial waves
which are unoccupied in the simple shell-model. The treatment of correlations
beyond the Brueckner-Hartree-Fock approximation also yields an improvement for
the calculated ground-state properties.Comment: 12 pages RevTeX, 7 figures postscript files appende
Analysis of three-nucleon forces effects in the system
Using modern nucleon-nucleon interactions in the description of the
nuclear systems the per datum results to be much bigger than one. In
particular it is not possible to reproduce the three- and four-nucleon binding
energies and the scattering length simultaneously. This is one
manifestation of the necessity of including a three-nucleon force in the
nuclear Hamiltonian. In this paper we perform an analysis of some, widely used,
three-nucleon force models. We analyze their capability to describe the
aforementioned quantities and, to improve their description, we propose
modifications in the parametrization of the models. The effects of these new
parametrization are studied in some polarization observables at low energies.Comment: 10 pages, to be published in Few-Body Systems. Presented at the
workshop on "Relativistic Description of Two- and Three-body Systems in
Nuclear Physics" ECT* Trento, 19 - 23 October 200
Mass Dependence of M3Y-Type Interactions and the Effects of Tensor Correlations
The mass dependence of the M3Y-type effective interactions and the effects of
tensor correlations are examined. Two-body nuclear matrix elements are obtained
by the lowest order constrained variational (LOCV) technique with and without
tensor correlations. We have found that the tensor correlations are important
especially in the triplet-even (TE) and tensor-even (TNE) channels in order to
reproduce the G-matrix elements obtained previously. Then M3Y-type potentials
for inelastic scattering are obtained by fitting our two-body matrix elements
to those of a sum of Yukawa functions for the mass numbers A=24, A=40 and A=90.Comment: 13 pages, 6 table
Neutron matter at zero temperature with auxiliary field diffusion Monte Carlo
The recently developed auxiliary field diffusion Monte Carlo method is
applied to compute the equation of state and the compressibility of neutron
matter. By combining diffusion Monte Carlo for the spatial degrees of freedom
and auxiliary field Monte Carlo to separate the spin-isospin operators, quantum
Monte Carlo can be used to simulate the ground state of many nucleon systems
(A\alt 100). We use a path constraint to control the fermion sign problem. We
have made simulations for realistic interactions, which include tensor and
spin--orbit two--body potentials as well as three-nucleon forces. The Argonne
and two nucleon potentials plus the Urbana or Illinois
three-nucleon potentials have been used in our calculations. We compare with
fermion hypernetted chain results. We report results of a Periodic Box--FHNC
calculation, which is also used to estimate the finite size corrections to our
quantum Monte Carlo simulations. Our AFDMC results for models of pure
neutron matter are in reasonably good agreement with equivalent Correlated
Basis Function (CBF) calculations, providing energies per particle which are
slightly lower than the CBF ones. However, the inclusion of the spin--orbit
force leads to quite different results particularly at relatively high
densities. The resulting equation of state from AFDMC calculations is harder
than the one from previous Fermi hypernetted chain studies commonly used to
determine the neutron star structure.Comment: 15 pages, 15 tables and 5 figure
Selected Topics in Three- and Four-Nucleon Systems
Two different aspects of the description of three- and four-nucleon systems
are addressed. The use of bound state like wave functions to describe
scattering states in collisions at low energies and the effects of some
of the widely used three-nucleon force models in selected polarization
observables in the three- and four-nucleon systems are discussed.Comment: Presented at the 21st European Conference on Few-Body Problems in
Physics, Salamanca, Spain, 30 August - 3 September 201
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