182 research outputs found
Evolution of Nuclear Spectra with Nuclear Forces
We first define a series of NN interaction models ranging from very simple to
fully realistic. We then present Green's function Monte Carlo calculations of
light nuclei to show how nuclear spectra evolve as the nuclear forces are made
increasingly sophisticated. We find that the absence of stable five- and
eight-body nuclei depends crucially on the spin, isospin, and tensor components
of the nuclear force.Comment: 5 pages, 2 figures, submitted to Phys. Rev. Let
Correlations and Equilibration in Relativistic Quantum Systems
In this article we study the time evolution of an interacting field
theoretical system, i.e. \phi^4-field theory in 2+1 space-time dimensions, on
the basis of the Kadanoff-Baym equations for a spatially homogeneous system
including the self-consistent tadpole and sunset self-energies. We find that
equilibration is achieved only by inclusion of the sunset self-energy.
Simultaneously, the time evolution of the scalar particle spectral function is
studied for various initial states. We also compare associated solutions of the
corresponding Boltzmann equation to the full Kadanoff-Baym theory. This
comparison shows that a consistent inclusion of the spectral function has a
significant impact on the equilibration rates only if the width of the spectral
function becomes larger than 1/3 of the particle mass. Furthermore, based on
these findings, the conventional transport of particles in the on-shell
quasiparticle limit is extended to particles of finite life time by means of a
dynamical spectral function A(X,\vec{p},M^2). The off-shell propagation is
implemented in the Hadron-String-Dynamics (HSD) transport code and applied to
the dynamics of nucleus-nucleus collisions.Comment: 20 pages, 7 figures to appear in "Nonequilibrium at short time scales
- Formation of correlations", edited by K. Morawetz, Springer, Berlin (2003),
p16
Electromagnetic Scattering from Relativistic Bound States
The quasipotential formalism for elastic scattering from relativistic bound
states is formulated based on the instant constraint in the Breit frame. The
quasipotential electromagnetic current is derived from Mandelstam's five-point
kernel and obeys a two-body Ward identity. Breit-frame wave functions are
obtained directly by solving integral equations with nonzero total
three-momentum, thus accomplishing a dynamical boost. Calculations of
electron-deuteron elastic form factors illustrate the importance of the
dynamical boost versus kinematic boosts of the rest frame wave functions.Comment: RevTeX 3.0 manuscript, 9 pages. UU-file is a single PostScript file
of the manuscript including figures. U. MD PP #93-17
Note on the single-shock solutions of the Korteweg-de Vries-Burgers equation
The well-known shock solutions of the Korteweg-de Vries-Burgers equation are
revisited, together with their limitations in the context of plasma
(astro)physical applications. Although available in the literature for a long
time, it seems to have been forgotten in recent papers that such shocks are
monotonic and unique, for a given plasma configuration, and cannot show
oscillatory or bell-shaped features. This uniqueness is contrasted to solitary
wave solutions of the two parent equations (Korteweg-de Vries and Burgers),
which form a family of curves parameterized by the excess velocity over the
linear phase speed.Comment: Accepted for publication in Astrophysics & Space Scienc
Instant Two-Body Equation in Breit Frame
A quasipotential formalism for elastic scattering from relativistic bound
states is based on applying an instant constraint to both initial and final
states in the Breit frame. This formalism is advantageous for the analysis of
electromagnetic interactions because current conservation and four momentum
conservation are realized within a three-dimensional formalism. Wave functions
are required in a frame where the total momentum is nonzero, which means that
the usual partial wave analysis is inapplicable. In this work, the
three-dimensional equation is solved numerically, taking into account the
relevant symmetries. A dynamical boost of the interaction also is needed for
the instant formalism, which in general requires that the boosted interaction
be defined as the solution of a four-dimensional equation. For the case of a
scalar separable interaction, this equation is solved and the Lorentz
invariance of the three-dimensional formulation using the boosted interaction
is verified. For more realistic interactions, a simple approximation is used to
characterize the boost of the interaction.Comment: 20 pages in revtex 3, 3 figures. Fixed reform/tex errors
Particle production in quantum transport theories
The particle production in the intermediate energy heavy ion collisions is
discussed in the framework of the nonequilibrium Green's functions formalism.
The evolution equations of the Green's functions for fermions allows for the
discussion of the off-shell fermion propagator and of the large momentum
component in the initial state. For the case of a homogeneous system numerical
calculations of the meson production rate are performed and compared with the
semiclassical production rate.Comment: 45 pages, figures included, uses FEYNMAN macro
Total Photoabsorption Cross Sections of A=6 Nuclei with Complete Final State Interaction
The total photoabsorption cross sections of 6He and 6Li are calculated
microscopically with full inclusion of the six-nucleon final state interaction
using semirealistic nucleon-nucleon potentials. The Lorentz Integral Transform
(LIT) method and the effective interaction approach for the hyperspherical
formalism are employed. While 6Li has a single broad giant resonance peak,
there are two well separated peaks for 6He corresponding to the breakup of the
neutron halo and the alpha core, respectively. The comparison with the few
available experimental data is discussed.Comment: LaTeX, 8 pages, 3 ps 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
N-d scattering above the deuteron breakup threshold
The complex Kohn variational principle and the (correlated) Hyperspherical
Harmonics technique are applied to study the N--d scattering above the deuteron
breakup threshold. The configuration with three outgoing nucleons is explicitly
taken into account by solving a set of differential equations with outgoing
boundary conditions. A convenient procedure is used to obtain the correct
boundary conditions at values of the hyperradius fm. The
inclusion of the Coulomb potential is straightforward and does not give
additional difficulties. Numerical results have been obtained for a simple
s-wave central potential. They are in nice agreement with the benchmarks
produced by different groups using the Faddeev technique. Comparisons are also
done with experimental elastic N--d cross section at several energies.Comment: LaTeX, 13 pages, 3 figure
Photodisintegration of the triton with realistic potentials
The process is treated by means of three-body integral
equations employing in their kernel the W-Matrix representation of the
subsystem amplitudes. As compared to the plane wave (Born) approximation the
full solution of the integral equations, which takes into account the final
state interaction, shows at low energies a 24% enhancement. The calculations
are based on the semirealistic Malfliet-Tjon and the realistic Paris and Bonn B
potentials. For comparison with earlier calculations we also present results
for the Yamaguchi potential. In the low-energy region a remarkable potential
dependence is observed, which vanishes at higher energies.Comment: 16 pages REVTeX, 8 postscript figures included, uses epsfig.st
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