266 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
Explicit expressions for meromorphic solution of autonomous nonlinear ordinary differential equations
Meromorphic solutions of autonomous nonlinear ordinary differential equations
are studied. An algorithm for constructing meromorphic solutions in explicit
form is presented. General expressions for meromorphic solutions (including
rational, periodic, elliptic) are found for a wide class of autonomous
nonlinear ordinary differential equations
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
Exact solutions of equations for the Burgers hierarchy
Some classes of the rational, periodic and solitary wave solutions for the
Burgers hierarchy are presented. The solutions for this hierarchy are obtained
by using the generalized Cole - Hopf transformation
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
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
Light clusters in nuclear matter of finite temperature
We investigate properties and the distribution of light nuclei (A<4) in
symmetric nuclear matter of finite temperature within a microscopic framework.
For this purpose we have solved few-body Alt-Grassberger-Sandhas type equations
for quasi-nucleons that include self-energy corrections and Pauli blocking in a
systematic way. In a statistical model we find a significant influence in the
composition of nuclear matter if medium effects are included in the microscopic
calculation of nuclei. If multiplicities are frozen out at a certain time (or
volume), we expect significant consequences for the formation of light
fragments in a heavy ion collision. As a consequence of the systematic
inclusion of medium effects the ordering of multiplicities becomes opposite to
the law of mass action of ideal components. This is necessary to explain the
large abundance of -particles in a heavy ion collision that are
otherwise largely suppressed in an ideal equilibrium scenario.Comment: 9 pages, 9 figures, epja-style file
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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