323 research outputs found
On the nuclear symmetry energy and the neutron skin in neutron-rich nuclei
The symmetry energy for nuclear matter and its relation to the neutron skin
in finite nuclei is discussed. The symmetry energy as a function of density
obtained in a self-consistent Green function approach is presented and compared
to the results of other recent theoretical approaches. A partial explanation of
the linear relation between the symmetry energy and the neutron skin is
proposed. The potential of several experimental methods to extract the neutron
skin is examined.Comment: to appear in Phys. Rev.
Production of e+e- pairs in proton-deuteron capture to 3He
The process p+d \leftrightarrow 3He + \gamma* at intermediate energies is
described using a covariant and gauge-invariant model, and a realistic pd3He
vertex. Both photodisintegration of 3He and proton-deuteron capture with
production of e+e- pairs are studied, and results for cross sections and
response functions are presented. The effect of time-like formfactors on the
dilepton cross sections is investigated as well.Comment: 10 pages, 4 figures, Revtex, to be published in Physics Letters
Improved lower bounds for the ground-state energy of many-body systems
New lower bounds for the binding energy of a quantum-mechanical system of
interacting particles are presented. The new bounds are expressed in terms of
two-particle quantities and improve the conventional bounds of the Hall-Post
type. They are constructed by considering not only the energy in the
two-particle system, but also the structure of the pair wave function. We apply
the formal results to various numerical examples, and show that in some cases
dramatic improvement over the existing bounds is reached.Comment: 29 pages, 5 figures, to be published in Phys. Rev.
Center-of-mass effects on the quasi-hole spectroscopic factors in the 16O(e,e'p) reaction
The spectroscopic factors for the low-lying quasi-hole states observed in the
16O(e,e'p)15N reaction are reinvestigated with a variational Monte Carlo
calculation for the structure of the initial and final nucleus. A computational
error in a previous report is rectified. It is shown that a proper treatment of
center-of-mass motion does not lead to a reduction of the spectroscopic factor
for -shell quasi-hole states, but rather to a 7% enhancement. This is in
agreement with analytical results obtained in the harmonic oscillator model.
The center-of-mass effect worsens the discrepancy between present theoretical
models and the experimentally observed single-particle strength. We discuss the
present status of this problem, including some other mechanisms that may be
relevant in this respect.Comment: 14 pages, no figures, uses Revtex, to be published in Phys. Rev. C 58
(1998
Correlation effects in single-particle overlap functions and one-nucleon removal reactions
Single-particle overlap functions and spectroscopic factors are calculated on
the basis of the one-body density matrices (ODM) obtained for the nucleus
employing different approaches to account for the effects of
correlations. The calculations use the relationship between the overlap
functions related to bound states of the (A-1)-particle system and the ODM for
the ground state of the A-particle system. The resulting bound-state overlap
functions are compared and tested in the description of the experimental data
from (p,d) reactions for which the shape of the overlap function is important.Comment: 11 pages, 4 figures include
Electromagnetic interaction in chiral quantum hadrodynamics and decay of vector and axial-vector mesons
The chiral invariant QHD-III model of Serot and Walecka is applied in the calculation of some meson properties. The electromagnetic interaction is included by extending the symmetry of the model to the local U(1) \times SU(2)_{R} \times SU(2)_{L} group. The minimal and nonminimal contributions to the electromagnetic Lagrangian are obtained in a new representation of QHD-III. Strong decays of the axial-vector meson, a_{1} \to \pi \rho, a_{1} \to \pi \sigma, and the electromagnetic decays \rho \to \pi \pi \gamma, a_{1} \to \pi \gamma and \rho \to \pi \gamma are calculated. The low-energy parameters for the \pi-\pi scattering are calculated in the tree-level approximation. The effect of the auxiliary Higgs bosons, introduced in QHD-III in order to generate masses of the vector and axial-vector mesons via the Higgs mechanism, is studied as well. This is done on the tree level for \pi-\pi scattering and on the level of one-loop diagrams for the a_{1} \to \pi \gamma decay. It is demonstrated that the model successfully describes some features of meson phenomenology in the non-strange sector
Long-range correlations in finite nuclei: comparison of two self-consistent treatments
Long-range correlations, which are partially responsible for the observed fragmentation and depletion of low-lying single-particle strength, are studied in the Green's function formalism. The self-energy is expanded up to second order in the residual interaction. We compare two methods of implementing self-consistency in the solution of the Dyson equation beyond Hartree-Fock, for the case of the 16O nucleus. It is found that the energy-bin method and the BAGEL method lead to globally equivalent results. In both methods the final single-particle strength functions are characterized by exponential tails at energies far from the Fermi level
Solving the Richardson equations for Fermions
Forty years ago Richardson showed that the eigenstates of the pairing
Hamiltonian with constant interaction strength can be calculated by solving a
set of non-linear coupled equations. However, in the case of Fermions these
equations lead to singularities which made them very hard to solve. This letter
explains how these singularities can be avoided through a change of variables
making the Fermionic pairing problem numerically solvable for arbitrary single
particle energies and degeneracies.Comment: 5 pages, 4 figures, submitted to Phys.Rev.
Quasiparticle properties in a density functional framework
We propose a framework to construct the ground-state energy and density
matrix of an N-electron system by solving selfconsistently a set of
single-particle equations. The method can be viewed as a non-trivial extension
of the Kohn-Sham scheme (which is embedded as a special case). It is based on
separating the Green's function into a quasi-particle part and a background
part, and expressing only the background part as a functional of the density
matrix. The calculated single-particle energies and wave functions have a clear
physical interpretation as quasiparticle energies and orbitals.Comment: 12 pages, 1 figure, to be published in Phys. Rev.
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