128 research outputs found
Ground state correlations and mean-field in O
We use the coupled cluster expansion ( method) to generate the
complete ground state correlations due to the NN interaction. Part of this
procedure is the calculation of the two-body G matrix inside the nucleus in
which it is being used. This formalism is being applied to in a
configuration space of 50 . The resulting ground state wave
function is used to calculate the binding energy and one- and two-body
densities for the ground state of .Comment: 9 pages, 9 figures, LaTe
Ground state correlations and mean-field in O: Part II
We continue the investigations of the O ground state using the
coupled-cluster expansion [] method with realistic nuclear
interaction. In this stage of the project, we take into account the three
nucleon interaction, and examine in some detail the definition of the internal
Hamiltonian, thus trying to correct for the center-of-mass motion. We show that
this may result in a better separation of the internal and center-of-mass
degrees of freedom in the many-body nuclear wave function. The resulting ground
state wave function is used to calculate the "theoretical" charge form factor
and charge density. Using the "theoretical" charge density, we generate the
charge form factor in the DWBA picture, which is then compared with the
available experimental data. The longitudinal response function in inclusive
electron scattering for O is also computed.Comment: 9 pages, 7 figure
Neutron Drops and Skyrme Energy-Density Functionals
The J=0 ground state of a drop of 8 neutrons and the lowest
1/2 and 3/2 states of 7-neutron drops, all in an external well, are
computed accurately with variational and Green's function Monte Carlo methods
for a Hamiltonian containing the Argonne two-nucleon and Urbana IX
three-nucleon potentials. These states are also calculated using Skyrme-type
energy-density functionals. Commonly used functionals overestimate the central
density of these drops and the spin-orbit splitting of 7-neutron drops.
Improvements in the functionals are suggested
Quantum Monte Carlo calculations of nuclei
We report on quantum Monte Carlo calculations of the ground and low-lying
excited states of nuclei using realistic Hamiltonians containing the
Argonne two-nucleon potential alone or with one of several
three-nucleon potentials, including Urbana IX and three of the new Illinois
models. The calculations begin with correlated many-body wave functions that
have an -like core and multiple p-shell nucleons, -coupled to the
appropriate quantum numbers for the state of interest. After
optimization, these variational trial functions are used as input to a Green's
function Monte Carlo calculation of the energy, using a constrained path
algorithm. We find that the Hamiltonians that include Illinois three-nucleon
potentials reproduce ten states in Li, Be, Be, and B with
an rms deviation as little as 900 keV. In particular, we obtain the correct
3 ground state for B, whereas the Argonne alone or with
Urbana IX predicts a 1 ground state. In addition, we calculate isovector
and isotensor energy differences, electromagnetic moments, and one- and
two-body density distributions.Comment: 28 pages, 12 tables, 7 figure
Deduction of the quantum numbers of low-lying states of 6-nucleon systems based on symmetry
The inherent nodal structures of the wavefunctions of 6-nucleon systems have
been investigated. The existence of a group of six low-lying states dominated
by L=0 has been deduced. The spatial symmetries of these six states are found
to be mainly {4,2} and {2,2,2}.Comment: 8 pages, no figure
Microscopic calculation of the inclusive electron scattering structure function in O-16
We calculate the charge form factor and the longitudinal structure function
for O and compare with the available experimental data, up to a momentum
transfer of 4 fm. The ground state correlations are generated using the
coupled cluster [exp(S}] method, together with the realistic v-18 NN
interaction and the Urbana IX three-nucleon interaction. Center-of-mass
corrections are dealt with by adding a center-of-mass Hamiltonian to the usual
internal Hamiltonian, and by means of a many-body expansion for the computation
of the observables measured in the center-of-mass system
Spin-Isospin Structure and Pion Condensation in Nucleon Matter
We report variational calculations of symmetric nuclear matter and pure
neutron matter, using the new Argonne v18 two-nucleon and Urbana IX
three-nucleon interactions. At the equilibrium density of 0.16 fm^-3 the
two-nucleon densities in symmetric nuclear matter are found to exhibit a
short-range spin-isospin structure similar to that found in light nuclei. We
also find that both symmetric nuclear matter and pure neutron matter undergo
transitions to phases with pion condensation at densities of 0.32 fm^-3 and 0.2
fm^-3, respectively. Neither transtion occurs with the Urbana v14 two-nucleon
interaction, while only the transition in neutron matter occurs with the
Argonne v14 two-nucleon interaction. The three-nucleon interaction is required
for the transition to occur in symmetric nuclear matter, whereas the the
transition in pure neutron matter occurs even in its absence. The behavior of
the isovector spin-longitudinal response and the pion excess in the vicinity of
the transition, and the model dependence of the transition are discussed.Comment: 44 pages RevTeX, 15 postscript figures. Minor modifications to
original postin
Beyond the Shell Model: The Canonical Nuclear Many-Body Problem as an Effective Theory
We describe a strategy for attacking the canonical nuclear structure problem
---bound-state properties of a system of point nucleons interacting via a
two-body potential---which involves an expansion in the number of particles
scattering at high momenta, but is otherwise exact. The required
self-consistent solutions of the Bloch-Horowitz equation for effective
interactions and operators are obtained by an efficient Green's function method
based on the Lanczos algorithm. We carry out this program for the simplest
nuclei, d and He, to contrast a rigorous effective theory with the shell
model, thereby illustrating several of the uncontrolled approximations in the
latter.Comment: Revtex; two columns; four pages; two figures; submitted to Phys. Rev.
Let
Quantum Monte Carlo Calculations of Pion Scattering from Li
We show that the neutron and proton transition densities predicted by recent
quantum Monte Carlo calculations for A=6,7 nuclei are consistent with pion
scattering from 6Li and 7Li at energies near the Delta resonance. This has
provided a microscopic understanding of the enhancement factors for quadrople
excitations, which were needed to describe pion inelastic scattering within the
nuclear shell model of Cohen and Kurath.Comment: 10 pages, REVTeX, 3 postscript figures; added calculation of elastic
and inelastic pion scattering from 6Li at multiple energie
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