title:
Parity-Violating Electron Scattering from the Pion-Correlated
  Relativistic Fermi Gas

abstract:
  Parity-violating quasielastic electron scattering is studied within the
context of the relativistic Fermi gas and its extensions to include the effects
of pionic correlations and meson-exchange currents. The work builds on previous
studies using the same model; here the part of the parity-violating asymmetry
that contains axial-vector hadronic currents is developed in detail using those
previous studies and a link is provided to the transverse vector-isovector
response. Various integrated observables are constructed from the differential
asymmetry. These include an asymmetry averaged over the quasielastic peak, as
well as the difference of the asymmetry integrated to the left and right of the
peak -- the latter is shown to be optimal for bringing out the nature of the
pionic correlations. Special weighted integrals involving the differential
asymmetry and electromagnetic cross section, based on the concepts of y-scaling
and sum rules, are constructed and shown to be suited to studies of the
single-nucleon form factor content in the problem, in particular, to
determinations of the isovector/axial-vector and electric strangeness form
factors. Comparisons are also made with recent predictions made on the basis of
relativistic mean-field theory.


title: Calculation of the properties of the rotational bands of $^{155,157}$Gd

abstract:
  We reexamine the long-standing problem of the microscopic derivation of a
particle-core coupling model. We base our research on the Klein-Kerman
approach, as amended by D\"onau and Frauendorf. We describe the formalism to
calculate energy spectra and transition strengths in some detail. We apply our
formalism to the rotational nuclei $^{155,157}$Gd, where recent experimental
data requires an explanation. We find no clear evidence of a need for Coriolis
attenuation.


title: The Skyrme model description of the spin-orbit force

abstract:
  We examine the derivation of the spin-orbit force from the Skyrme model. We
find substantial agreement with phenomenological potentials. We show that a
systematic and simultaneous treatment of all components of the kinetic energy
introduces a minus sign relative to previous calculations for the iso-spin
independent part of the interaction. We also explain the smallness of the
iso-spin dependent part of the spin-orbit potential.


title:
Inertial parameters of the Skyrmion-Skyrmion system with the product
  ansatz

abstract:
  The kinetic energy of the Skyrmion-Skyrmion system is calculated in the
product ansatz. The energy is expanded in a set of rotationally invariant
quadratic functions of translational and iso-rotational velocities in the
product ansatz and all inertial parameters are evaluated. Most of the iso-spin
dependent parameters are small at separations larger than 1 fm. However, some
parameters of the coupling between the iso-rotational velocities of the
Skyrmions decay slowly, as $1/R$, when zero pion mass is used. Otherwise we
find that the results are not sensitive to the addition of the pion mass term.


title: Masses of Multiquark Droplets

abstract:
  The mass formulae for finite lumps of strange quark matter with $u$, $d$ and
$s$ quarks, and non-strange quark matter consisting of $u$ and $d$ quarks are
derived in a non-relativistic potential model. The finite-size effects
comprising the surface, curvature and even, the Gauss curvature were
consistently obtained, which shows a converging trend. It is found that there
is a possibility for the formation of metastable strangelets of large mass. The
model predicts low charge to mass ratio as the characteristic signature of
strange matter in agreement with the relativistic studies. This study also
yields an independent estimate for the bag energy density $B$, which is in
agreement with the M.I.T bag model value.


title:
Demonstration of the auxiliary-field Monte Carlo approach for sd-shell
  nuclei

abstract:
  We apply the auxiliary-field Monte Carlo approach to the nuclear shell model
in the 1s-0d configuration space. The Hamiltonian was chosen to have isovector
pairing and isoscalar multipole-multipole interactions, and the calculations
were performed within the fixed-particle, canonical ensemble. The results
demonstrate the feasibility of the method for $N\neq Z$ even-even and odd-odd
N=Z nuclei. In particular, static observables for even-even Ne isotopes and
Na-22 compare well with results obtained from exact diagonalization of the
Hamiltonian. Response functions are presented for Ne-22 and compared with exact
results, and the viability of cranked calculations for $N\neq Z$ even-even
nuclei is addressed. We present methods for computing observables in the
canonical ensemble using Fourier extraction, and for determining the nuclear
shape.


title:
Study of the Three-Nucleon (e,e') Longitudinal Response Function with a
  New Approach

abstract:
  A new method for studying the many-body response functions is elaborated and
first applied to the $^3$He longitudinal response. An integral transform of the
response function is calculated from the bound-state-type equations for several
versions of the N-N force. The equations are solved with the help of the
hyperspherical expansion. The final-state interaction is completely taken into
account. The results are compared with the integral transform of the
experimental response function for 250 MeV/c$\leq q \leq 500$ MeV/c. The
difference amounts to 20-25\% with the experimental response substantially
exceeding the theoretical one in the low-energy region.


title: Thermal phenomenology of hadrons from 200 AGeV S+S collisions

abstract:
  We develop a complete and consistent description for the hadron spectra from
heavy ion collisions in terms of a few collective variables, in particular
temperature, longitudinal and transverse flow. To achieve a meaningful
comparison with presently available data, we also include the resonance decays
into our picture. To disentangle the influences of transverse flow and
resonance decays in the $m_T$-spectra, we analyse in detail the shape of the
$m_T$-spectra.


title:
Classical mappings of the symplectic model and their application to the
  theory of large-amplitude collective motion

abstract:
  We study the algebra Sp(n,R) of the symplectic model, in particular for the
cases n=1,2,3, in a new way. Starting from the Poisson-bracket realization we
derive a set of partial differential equations for the generators as functions
of classical canonical variables. We obtain a solution to these equations that
represents the classical limit of a boson mapping of the algebra. The
relationship to the collective dynamics is formulated as a theorem that
associates the mapping with an exact solution of the time-dependent Hartree
approximation. This solution determines a decoupled classical symplectic
manifold, thus satisfying the criteria that define an exactly solvable model in
the theory of large amplitude collective motion. The models thus obtained also
provide a test of methods for constructing an approximately decoupled manifold
in fully realistic cases. We show that an algorithm developed in one of our
earlier works reproduces the main results of the theorem.


title: Intermediate-Energy Semileptonic Probes of the Hadronic Neutral Current

abstract:
  The present and future prospects of intermediate-energy semileptonic neutral
current studies are reviewed. Possibilities for using neutrino and
parity-violating electron scattering from nucleons and nuclei to study hadron
structure and nuclear dynamics are emphasized, with particular attention paid
to probes of the nucleon's strangeness content. Connections are drawn between
such studies and tests of electroweak gauge theory using electron or neutrino
scattering. Outstanding theoretical issues in the interpretation of
semileptonic neutral current measurements are highlighted, and the prospects
for undertaking neutrino and parity-violating electron scattering experiments
in the near future are surveyed.


title:
Particle-drip lines from the Hartree-Fock-Bogoliubov theory with Skyrme
  interaction

abstract:
  We calculate positions of one- and two-particle, proton and neutron drip
lines within the Hartree-Fock-Bogoliubov theory using Skyrme interaction. We
also determine an approximate $r$-process path defined as a line where the
neutron binding energy is equal to 2~MeV. A weakening of the nuclear shell
structure at drip lines is found and interpreted as resulting from a coupling
with continuum states.


title:
Study of High Energy Heavy-Ion Collisions in a Relativistic BUU-Approach
  with Momentum-Dependent Mean-Fields

abstract:
  We introduce momentum-dependent scalar and vector fields into the Lorentz
covariant relativistic BUU- (RBUU-) approach employing a polynomial ansatz for
the relativistic nucleon-nucleon interaction. The momentum-dependent
parametrizations are shown to be valid up to about 1 GeV/u for the empirical
proton-nucleus optical potential. We perform numerical simulations for
heavy-ion collisions within the RBUU-approach adopting momentum-dependent and
momentum-independent mean-fields and calculate the transverse flow in and
perpendicular to the reaction plane, the directivity distribution as well as
subthreshold K+-production. By means of these observables we discuss the
particular role of the momentum-dependent forces and their implications on the
nuclear equation of state. We find that only a momentum-dependent parameter-set
can explain the experimental data on the transverse flow in the reaction plane
from 150 - 1000 MeV/u and the differential K+-production cross sections at 1
GeV/u at the same time.


title: Perturbative Gluon Shadowing in Heavy Nuclei

abstract:
  We study how much gluon shadowing can be perturbatively generated through the
modified QCD evolution in heavy nuclei. The evolution of small-$x$ gluons is
investigated within the semiclassical approximation. The method of
characteristics is used to evaluate the shadowed distributions in low-$Q$ and
small-$x$ region. In solving the modified evolution equation, we model in
simultaneously fusions from independent constituents and from the same
constituent, both in a proton and in a large loosely bound nucleus of $A\sim
200$. In addition to the actual distributions at small $x$, we study the ratios
of the distributions at an initial scale $Q_0 = 2$ GeV, and show that a strong
nuclear shadowing can follow from the modified QCD evolution.


title:
Analysis of the instantaneous Bethe-Salpeter equation for
  \(q\bar{q}\)-bound-states

abstract:
  We investigate the structure of the instantaneous Bethe-Salpeter equation for
\(q\bar{q}\)-bound states in the general case of unequal quark masses and
develop a numerical scheme for the calculation of mass spectra and
Bethe-Salpeter amplitudes. In order to appreciate the merits of the various
competing models beyond the reproduction of the mass spectra we present
explicit formulas to calculate electroweak decays. The results for an explicit
quark model will be compared to experimental data in a subsequent paper


title: A Bethe-Salpeter model for light mesons: spectra and decays

abstract:
  The spectra and electroweak decay properties of light mesons are analyzed
within the framework of the instantaneous Bethe-Salpeter equation. The
interaction kernel comprises alternative spin-structures for a parameterization
of confinement and a residual quark-antiquark interaction based on instanton
effects. It is shown that only with a vector confinement the parameters can be
chosen such as to yield an excellent description of the light pseudoscalar and
vector mesons including weak and two photon decays. However it is found that it
is not possible to reconcile this with the Regge behavior of higher lying meson
states with the same parameter set.


title: Microscopic Calculation of in-Medium Nucleon-Nucleon Cross Ssections

abstract:
  We derive in-medium nucleon-nucleon (NN) cross sections in a microscopic
model. Our calculations are based upon the Bonn NN potential and the
Dirac-Brueckner approach for nuclear matter. We consider energies up to 300 MeV
(in the laboratory frame) and densities up to twice nuclear matter density. Our
results deviate substantially from cross section parametrizations that are
commonly used in the nuclear medium.


title: K$^+$-nucleus quasielastic scattering

abstract:
  K$^+$--nucleus quasielastic cross sections measured for a laboratory kaon
beam momentum of 705 MeV/$c$ are presented for 3--momentum transfers of 300 and
500 MeV/$c$. The measured differential cross sections for C, Ca and Pb at 500
MeV/$c$ are used to deduce the effective number of nucleons participating in
the scattering, which are compared with estimates based on the eikonal
approximation. The long mean free path expected for K$^+$ mesons in nuclei is
found. Double differential cross sections for C and Ca are compared to
relativistic nuclear structure calculations.


title: Finite Temperature Many-Body Theory with the Lipkin Model

abstract:
  We have compared exact numerical results for the Lipkin model at finite
temperature with Hartree-Fock theory and with the results of including in
addition the ring diagrams. In the simplest version of the Lipkin model the
Hartree-Fock approach shows a ``phase transition" which is absent in the exact
results. For more realistic cases, Hartree-Fock provides a very good
approximation and a modest improvement is obtained by adding the ring diagrams.


title:
An Effective Lagrangian with Broken Scale and Chiral Symmetry Applied to
  Nuclear Matter and Finite Nuclei

abstract:
  We study nuclear matter and finite nuclei with a chiral Lagrangian which
generalizes the linear $\sigma$ model and also accounts for the QCD trace
anomaly by means of terms which involve the $\sigma$ and $\vmg{\pi}$ fields as
well as the glueball field $\phi$. The form of the scale invariant term leading
to an omega meson mass, after symmetry breaking, could involve coupling to
$\phi^2$ or $\sigma^2$ or some linear combination thereof. In fact an
$\omega_{\mu}\omega^{\mu}\phi^2$ form is strongly favored by the bulk
properties of nuclei, which also rather strongly constrain the other
parameters. A reasonable description of the closed shell nuclei oxygen, calcium
and lead can be achieved, although the spin-orbit splittings are somewhat
smaller than the experimental values.


title: A Cloudy Bag Model for the S-D Wave $\Kbar-N$ System

abstract:
  The cloudy quark bag model is applied to the coupled ($\Kbar N$, $\Sigma
\pi$, $\Lambda \pi$) system for $S-D$ partial waves. Energy--dependent
separable potentials are derived, as are new numerical algorithms for solving
the coupled Lippmann-Schwinger equations. The parameters are fit to $K^-p$
scattering and reaction cross sections, branching ratios, and mass spectra from
$K^-p\rightarrow \Sigma\pi\pi\pi, \Lambda\pi\pi\pi$. The $\Sigma_{P13}(1385)$
and $\Lambda_{D03}(1520)$ resonances are found to be predominately elementary
bag states with considerable dressing for the $\Sigma_{P13}$. The
$\Lambda_{S01}(1405)$ appears as a complicated composite systems arising from
two poles.


title: Nucleon Flow and Fragment Flow in Heavy Ion Reactions

abstract:
  The collective flow of nucleons and that of fragments in the 12C + 12C
reaction below 150 MeV/nucleon are calculated with the antisymmetrized version
of molecular dynamics combined with the statistical decay calculation. Density
dependent Gogny force is used as the effective interaction. The calculated
balance energy is about 100 MeV/nucleon, which is close to the observed value.
Below the balance energy, the absolute value of the fragment flow is larger
than that of nucleon flow, which is also in accordance with data. The
dependence of the flow on the stochastic collision cross section and its origin
are discussed. All the results are naturally understood by introducing the
concept of two components of flow: the flow of dynamically emitted nucleons and
the flow of the nuclear matter which contributes to both the flow of fragments
and the flow of nucleons due to the statistical decay.


title:
Inclusive scattering of electrons from nuclear matter in the few GeV
  range

abstract:
  We study Final State Interaction effects (FSI) in inclusive electron
scattering of several GeV from nuclear matter. We consider separately the cases
of 'elastic' and 'inelastic' knockout of respectively a nucleon and a
non-nucleonic particle. For the former category FSI have been calculated, using
the first cumulant approximation of a relativistic generalization of the theory
of Gersch et al, including intermediate NN states states with produced hadrons.
We also discuss a formal expression for the first cumulant approximation on the
basis of the PWIA. FSI between an inelasticlly knocked-out particle and core
nucleons are neglected. We present two scaling analyses of the data, from which
the above 'inelastic' contributions have been been removed. The data expressed
in a relativistic West variable show scaling of a much better quality than the
same in the IA scaling variable. Predictions for inclusive cross sections in
the two first cumulant versions are presented and discussed. We make a critical
comparison of the above with the IA approach of Benhar et al and their results.


title:
Finite Volume Effect of Nucleons and the Formation of the Quark-Gluon
  Plasma

abstract:
  We study a thermodynamically consistent implementation of the nucleon volume
in the mean field theory, and find that this volume has large consequences on
the properties of hadronic matter under extreme conditions such as in
astrophysical objects and high energy heavy-ion collisions. It is shown that we
can reproduce the critical temperature $T_{c}\simeq 200$ MeV predicted by
lattice QCD calculations for the phase transition from hadronic matter to
quark-gluon plasma, by using parameters which are adjusted to fit all empirical
data for normal nuclear matter.


title: On the Relativistic Description of the Nucleus

abstract:
  We discuss a relativistic theory of the atomic nuclei in the framework of the
hamiltonian formalism and of the mesonic model of the nucleus. Attention is
paid to the translational invariance of the theory. Our approach is centered on
the concept of spectral amplitude, a function in the Dirac spinor space. We
derive a Lorentz covariant equation for the latter, which requires as an input
the baryon self-energy. For this we either postulate the most general
Lorentz-Poincar\'e invariant expression or perform a calculation via a
Bethe-Salpeter equation starting from a nucleon-nucleus interaction. We discuss
the features of the nuclear spectrum obtained in the first instance. Finally
the general constraints the self-energy should satisfy because of analyticity
and Poincar\'e covariance are discussed.


title:
Momentum-Dependent Mean Field Based Upon the Dirac-Brueckner Approach
  for Nuclear Matter

abstract:
  A momentum-dependent mean field potential, suitable for application in the
transport-model description of nucleus-nucleus collisions, is derived in a
microscopic way. The derivation is based upon the Bonn meson-exchange model for
the nucleon-nucleon interaction and the Dirac-Brueckner approach for nuclear
matter. The properties of the microscopic mean field are examined and compared
with phenomenological parametrizations which are commonly used in
transport-model calculations.


title: Variational Methods for Nuclear Systems with Dynamical Mesons

abstract:
  We derive a model Hamiltonian whose ground state expectation value of any
two-body operator coincides with that obtained with the Jastrow correlated wave
function of the many-body Fermi system. Using this Hamiltonian we show that the
variational principle can be extended to treat systems with dynamical mesons,
even if in this case the concept of wave function looses its meaning.


title: Pionic Bound States in Momentum Space

abstract:
  Bound states of the pion--nucleus system are investigated in momentum space
using a microscopic optical potential with inherent energy dependences and
nonlocalities arising from elementary potential models. The wave equation and
computational techniques are tested, shallow levels are calculated, and a
comparison is made with experiment. Deep levels are found to be deeper and
broader than those in other investigations.


title: How important is the three-nucleon force?

abstract:
  By calculating the contribution of the $\pi-\pi$ three-body force to the
three-nucleon binding energy in terms of the $\pi N$ amplitude using
perturbation theory, we are able to determine the contribution of the different
$\pi N$ partial waves to the three-nucleon force. The division of the $\pi N$
amplitude into a pole and nonpole gives a unique procedure for the
determination of the $\pi NN$ form factor in the model. The total contribution
of the three-body force to the binding energy of the triton is found to be very
small.


title: Low-energy M1 and E3 excitations in the proton-rich Kr-Zr region

abstract:
  Low-energy intrinsic $K^\pi$=1$^+$, $0^-$, $1^-$, $2^-$, and $3^-$ states in
the even-even proton-rich Sr, Kr, and Zr nuclei are investigated using the
quasiparticle random phase approximation. In the Z$\simeq$N nuclei the
lowest-lying 1$^+$ states are found to carry unusually large $B(M1)$ strength.
It is demonstrated that, unlike in the heavier nuclei, the octupole
collectivity in the light zirconium region is small and, thus, is not directly
correlated with the systematics of the lowest negative parity states.


title:
Relativistic Microscopic Description of Proton-Nucleus Scattering at
  Intermediate Energies

abstract:
  We study elastic proton-nucleus scattering at intermediate energies. The
nucleon-nucleus optical potential is derived from the Bonn nucleon-nucleon
potential and the Dirac-Brueckner approach for nuclear matter. Our
calculations, which do not contain any adjustable parameters, yield good
agreement with experiment.


title: A Gauge Invariant Unitary Theory for Pion Photoproduction

abstract:
  A covariant, unitary and gauge invariant theory for pion photoproduction on a
single nucleon is presented. To achieve gauge invariance at the operator level
one needs to include both the $\pi N$ and $\gamma\pi N$ thresholds. The final
amplitude can be written in terms of a distorted wave in the final $\pi N$
channel provided one includes additional diagrams to the standard Born term in
which the photon is coupled to the final state pion and nucleon. These
additional diagrams are required in order to satisfy gauge invariance.


title: Bose-condensation through resonance decay

abstract:
  We show that a system described by an equation of state which contains a high
number of degrees of freedom (resonances) can create a considerable amount of
superfluid (condensed) pions through the decay of short-lived resonances, if
baryon number and entropy are large and the dense matter decouples from
chemical equilibrium earlier than from thermal equilibrium. The system cools
down faster in the presence of a condensate, an effect that may partially
compensate the enhancement of the lifetime expected in the case of
quark-gluon-plasma formation.


title: Microscopic Calculation of in-Medium Proton-Proton Cross Sections

abstract:
  We derive in-medium PROTON-PROTON cross sections in a microscopic model based
upon the Bonn nucleon-nucleon potential and the Dirac-Brueckner approach for
nuclear matter. We demonstrate the difference between proton-proton and
neutron-proton cross sections and point out the need to distinguish carefully
between the two cases. We also find substantial differences between our
in-medium cross sections and phenomenological parametrizations that are
commonly used in heavy-ion reactions.


title:
Effective Masses and Sizes of N(939), $\Delta\!\!\mbox{\boldmath(1232)}$
  and N(1440) in Nuclear Medium

abstract:
  The effective masses and sizes of N(939), $\Delta(1232)$ and N(1440) in
nuclear medium are calculated for a model in which quarks are subjected to a
confinement force quenched by the scalar part of nuclear interactions. At the
nuclear matter density, the nucleon swells by 50\% relative to the free
nucleon. The masses of $\Delta(1232)$ and N(1440) decrease in nuclear medium
more than the nucleon, so that the pion requires less energy to excite them in
nuclear medium than it does for a free nucleon.


title:
Microscopic description of nuclei in the middle of the pf-shell by a
  shell model calculation with G-matrix interaction

abstract:
  Energy levels and electromagnetic properties of with $N=28\sim 30$ nuclides
are studied in terms of a large-scale shell model calculation, which contains
no newly adjusted parameters. The Kuo-Brown $G$-matrix interaction is shown to
reproduce energy levels of 205 low-lying states of these nuclei. We evaluate
effective charges by incorporating the core-polarization effects caused by the
coupling to GQR's. We then compute E2 moments and transition probabilities. The
M1 moments and transition rates are calculated by quoting the effective
$g$-factors of Towner, which are obtained by taking into account the
meson-exchange and the core-polarization mechanisms. By this microscopic
calculation most of the E2 properties and the magnetic moments are reproduced.
Although there are agreements and disagreements in the M1 transition rates, the
general tendency is reproduced. The $(e,e')$ and $(p,p')$ excitation from the
ground state to some low-lying $2^+$ states is also discussed.


title:
On the Analytic Structure of the Quark Self-Energy in Nambu-Jona-
  Lasinio Models

abstract:
  The self-energy of quarks is investigated for various models which are
inspired by the Nambu--Jona-Lasinio (NJL) model. Including, beyond the
Hartree-Fock approximation, terms up to second-order in the quark interaction,
the real and imaginary parts of scalar and vector components of the self-energy
are discussed. The second-order contributions depend on the energy and momentum
of the quark under consideration. This leads to solutions of the Dirac equation
which are significantly different from those of a free quark or a quark with
constant effective mass, as obtained in the Hartree-Fock approximation.


title: Self-Consistent Relativistic Calculation of Nucleon Mean Free Path

abstract:
  We present a fully self-consistent and relativistic calculation of the
nucleon mean free path in nuclear matter and finite nuclei. Starting from the
Bonn potential, the Dirac-Brueckner-Hartree-Fock results for nuclear matter are
parametrized in terms of an effective $\sigma$-$\omega$ Lagrangian suitable for
the relativistic density-dependent Hartree-Fock (RDHF) approximation. The
nucleon mean free path in nuclear matter is derived from this effective
Lagrangian taking diagrams up to fourth-order into account. For the nucleon
mean free path in finite nuclei, we make use of the density determined by the
RDHF calculation in the local density approximation. Our microscopic results
are in good agreement with the empirical data and predictions by Dirac
phenomenology.


title:
Nuclear recoil measurements in Superheated Superconducting Granule
  detectors

abstract:
  The response of Superheated Superconducting Granule (SSG) devices to nuclear
recoils has been explored by irradiating SSG detectors with a 70Me$\!$V neutron
beam. In the past we have tested Al SSG and more recently, measurements have
been performed with Sn and Zn detectors. The aim of the experiments was to test
the sensitivity of SSG detectors to recoil energies down to a few ke$\!$V. In
this paper, the preliminary results of the neutron irradiation of a SSG
detector made of Sn granules 15-20$\mu$m in diameter will be discussed. For the
first time, recoil energy thresholds of $\sim$1ke$\!$V have been measured.


title: Nuclear Ground-State Masses and Deformations

abstract:
  We tabulate the atomic mass excesses and nuclear ground-state deformations of
8979 nuclei ranging from $^{16}$O to $A=339$. The calculations are based on the
finite-range droplet macroscopic model and the folded-Yukawa single-particle
microscopic model. Relative to our 1981 mass table the current results are
obtained with an improved macroscopic model, an improved pairing model with a
new form for the effective-interaction pairing gap, and minimization of the
ground-state energy with respect to additional shape degrees of freedom. The
values of only 9 constants are determined directly from a least-squares
adjustment to the ground-state masses of 1654 nuclei ranging from $^{16}$O to
$^{263}$106 and to 28 fission-barrier heights. The error of the mass model is
0.669~MeV for the entire region of nuclei considered, but is only 0.448~MeV for
the region above $N=65$.


title:
Theory of Inclusive Scattering of Polarized Electrons by Polarized
  $^{3}$He and the Neutron Form Factors

abstract:
  The theory of inclusive lepton scattering of polarized leptons by polarized J
= 1/2 hadrons is presented and the origin of different expressions for the
polarized nuclear response function appearing in the literature is explained.
The sensitivity of the longitudinal asymmetry upon the neutron form factors is
investigated.


title: Chaotic Scattering in Heavy--Ion Reactions

abstract:
  We discuss the relevance of chaotic scattering in heavy--ion reactions at
energies around the Coulomb barrier. A model in two and three dimensions which
takes into account rotational degrees of freedom is discussed both classically
and quantum-mechanically. The typical chaotic features found in this
description of heavy-ion collisions are connected with the anomalous behaviour
of several experimental data.


title: Local $^4$He--p potentials from RGM phase shifts

abstract:
  Phase shifts for $\alpha$ + nucleon scattering generated by a multichannel
RGM model of the five-nucleon system are subjected to iterative-perturbative
``mixed-case" inversion for energies below the reaction threshold. The
resulting phase-equivalent potentials are compared with local potentials
calculated from the inversion of empirical phase shifts. A strong similarity is
revealed between the two sets of potentials, most notably in the description by
a parity- and energy-dependent local potential. In particular, the RGM-derived
and empirical potentials share a distinctive form of parity dependence in which
the odd-parity component is of greater radial extent. Comparison with
potentials representing single-channel RGM phase shifts exhibits the importance
of the coupled channels in terms of local potentials. The relative wave
functions derived from RGM are very different to those for the phase-equivalent
local potentials.


title: Relativistic description of electron scattering on the deuteron

abstract:
  Within a quasipotential framework a relativistic analysis is presented of the
deuteron current. Assuming that the singularities from the nucleon propagators
are important, a so-called equal time approximation of the current is
constructed. This is applied to both elastic and inelastic electron scattering.
As dynamical model the relativistic one boson exchange model is used.
Reasonable agreement is found with a previous relativistic calculation of the
elastic electromagnetic form factors of the deuteron. For the unpolarized
inelastic electron scattering effects of final state interactions and
relativistic corrections to the structure functions are considered in the
impulse approximation. Two specific kinematic situations are studied as
examples.


title: Hanbury-Brown--Twiss Analysis in a Solvable Model

abstract:
  The analysis of meson correlations by Hanbury-Brown--Twiss interferometry is
tested with a simple model of meson production by resonance decay. We derive
conditions which should be satisfied in order to relate the measured momentum
correlation to the classical source size. The Bose correlation effects are
apparent in both the ratio of meson pairs to singles and in the ratio of like
to unlike pairs. With our parameter values, we find that the single particle
distribution is too distorted by the correlation to allow a straightforward
analysis using pair correlation normalized by the singles rates. An analysis
comparing symmetrized to unsymmetrized pairs is more robust, but nonclassical
off-shell effects are important at realistic temperatures.


title:
Approximate Treatment of Hermitian Effective Interactions and a Bound on
  the Error

abstract:
  The Hermitian effective interaction can be well-approximated by
(R+R^dagger)/2 if the eigenvalues of omega^dagger omega are small or
state-independent(degenerate), where R is the standard non-Hermitian effective
interaction and omega maps the model-space states onto the excluded space. An
error bound on this approximation is given.


title:
Roles of triaxiality and residual interaction in signature inversions of
  A~130 odd-odd nuclei

abstract:
  Rotational bands with (neutron h_11/2)^1 (proton h_11/2)^1 configurations are
studied using a particle-rotor model in which a proton and a neutron
quasiparticles interacting through a zero-range force are coupled with a
triaxial rotor. It is shown for 124Cs that one can reproduce the signature
dependence of energy and B(M1)/B(E2) ratio best when one takes into account
gamma-deformations with irrotational-flow moment of inertia in addition to the
proton-neutron interaction proposed by Semmes and Ragnarsson. Including both
effects, a systematic calculation of signature splittings is performed for Cs,
La isotopes and N=75 isotones to be compared with experiments. Discussions are
also done on the deficiencies of the cranking model concerning its
applicability to signature inversion phenomena in odd-odd nuclei.


title: Pairproduction in a semiclassical transport theory

abstract:
  In high-energy nucleon-nucleon-collisions large meson production rates are
observed. As an alternative to meson exchange models here we propose a
nonperturbative treatment of the quark-antiquark production from the mean field
of colliding nucleon bags. Source terms for particles and antiparticles are
developed in a semiclassical quark transport description and the time evolution
of the quark density is studied for different mean fields numerically.


title: Meson-Exchange Currents and the Strangeness Radius of 4he

abstract:
  Meson-exchange current contributions to the strangeness radius of $^4$He are
computed in the one-boson exchange approximation. It is found that these
contributions introduce a $\lapp$10\% correction to the one-body contribution.
They should not, therefore, hamper the extraction of the nucleon strangeness
radius from the parity-violating electron-$^4$He asymmetry.


title:
Two-body matrix elements of Pauli-projected excentric single-particle
  orbits

abstract:
  We present explicit analytical formulae for two-body matrix elements between
Pauli-projected single-particle orbits generated by gaussians shifted from the
centre of a nuclear core, which is populated by nucleons occupying
harmonic-oscillator orbits. Such shifted gaussian orbits appear in the
generator-coordinate model of two-cluster systems and, as ingredients of
generating functions, in the resonating group model as well. A Pauli projection
is to be understood as a projection onto the subspace not occupied by the core
nucleons. This is an exact procedure to take into account the Pauli principle
in the limit in which the core is infinitely heavy, thus the procedure to be
presented is very useful in the microscopic description of large-core plus
small-cluster systems, such as involved in $\alpha$-decay problems.


title:
A combined mathematica--fortran program package for analytical
  calculation of the matrix elements of the microscopic cluster model

abstract:
  We present a computer code that analytically evaluates the matrix elements of
the microscopic nuclear Hamiltonian and unity operator between Slater
determinants of displaced gaussian single particle orbits. Such matrix elements
appear in the generator coordinate model and the resonating group model
versions of the microscopic multicluster calculations.


title: Nucleon polarization in three-body models of polarized \bbox{^6}Li

abstract:
  Just as $^3\roarrow{\rm He}$ can be approximately characterized as a
polarized neutron target, polarized \Li6D has been advocated as a good {\em
isoscalar} nuclear target for the extraction of the polarized gluon content of
the nucleon. The original argument rests upon a presumed ``alpha + deuteron''
picture of \Li6, with the polarization of the nucleus carried by the
polarization of the deuteron. We have calculated the polarization of the
constituents of \Li6 as a three-body bound state of $\alpha + n + p$
interacting with local potentials fitted to the scattering data. It is
necessary to include partial waves up to $j=17/2$ (75 channels, or, when
including the $T=1$ state, 150 channels) in the Faddeev equations before the
energy eigenvalue converges. The longitudinal formfactors are then described
well by the wave function. Various combinations of $\alpha$N and NN strong and
Coulomb potentials yield a straight line in the charge radius {\em vs.} energy
plane which, unlike those of previous calculations, passes through the
experimental datum. We find for all cases a polarization of the valence neutron
in excess of 90\%. This may make polarized \Li6D an attractive target for many
nuclear physics purposes, since its neutrons are effectively 45\% polarized.


title: Quantum fragmentation

abstract:
  Phenomenological and theoretical aspects of fragmentation for elementary
particles (resp. nuclei) are discussed. It is shown that some concepts of
classical fragmentation remain relevant in a microscopic framework, exhibiting
non-trivial properties of quantum relativistic field theory (resp. lattice
percolation). Email contact: pesch@amoco.saclay.cea.fr


title:
First-Forbidden beta decay: Medium enhancement of the axial charge at
  A=16

abstract:
  Calculations are presented for four relatively strong first-forbidden $\beta$
decays in the region A=11-16 in order to study the very large
mesonic-exchange-current enhancement of the rank-zero components. The $\mu^-$
capture on $^{16}$O is considered on the same footing. The wave functions
utilized include up to 4$\hbar\omega$ excitations. Two-body exchange-current
matrix elements are calculated as well as one-body impulse approximation matrix
elements. The resultant enhancement factor that multiplies the
impulse-approximation axial-charge matrix element is thereby determined by
comparison to experiment to be $\epsilon_{exp}$ = 1.61 $\pm$ 0.03 from three
$\beta^-$ decays and $\mu^-$ capture on $^{16}$O, which is in excellent
agreement with meson-exchange calculations in the soft-pion approximation.


title: Nuclear Fragmentation and Its Parallels

abstract:
  A model for the fragmentation of a nucleus is developed. Parallels of the
description of this process with other areas are shown which include Feynman's
theory of the $\lambda$ transition in liquid Helium, Bose condensation, and
Markov process models used in stochastic networks and polymer physics. These
parallels are used to generalize and further develop a previous exactly
solvable model of nuclear fragmentation. An analysis of some experimental data
is given.


title: Combinatorial nuclear level density by a Monte Carlo method

abstract:
  We present a new combinatorial method for the calculation of the nuclear
level density. It is based on a Monte Carlo technique, in order to avoid a
direct counting procedure which is generally impracticable for high-A nuclei.
The Monte Carlo simulation, making use of the Metropolis sampling scheme,
allows a computationally fast estimate of the level density for many fermion
systems in large shell model spaces. We emphasize the advantages of this Monte
Carlo approach, particularly concerning the prediction of the spin and parity
distributions of the excited states, and compare our results with those derived
from a traditional combinatorial or a statistical method. Such a Monte Carlo
technique seems very promising to determine accurate level densities in a large
energy range for nuclear reaction calculations.


title: Fission Decay Rates Determined from a Quantal Transport Equation

abstract:
  The decay of a metastable system is described by extending Kramers' method to
the quantal regime. For temperatures above twice the crossover value we recover
the result known from applying Euclidean path integrals to solvable models. Our
derivation is not restricted to a linearly coupled heat bath of oscillators,
and thus applicable to nuclear systems.


title: Microscopic approach to collective motion

abstract:
  An overview of a microscopic framework based on the Hartree-Fock description
of the mean field is presented which, starting from an effective interaction
allows a description of collective motions. A study of the isotope shifts in
the Pb region illustrates the importance of the effective interactions and
points to their limitations. Such forces should be improved in order to achieve
a better description of nuclei properties especially with the coming
availability of exotic beam facilities. The coupling of collective quadrupole
and octupole degrees of freedom in $^{194}$Pb is analyzed within the Generator
Coordinate Method, which represents a step beyond the simple mean-field
approximation. As a last example, we present a study of nuclear rotations.
First we discuss results on superdeformed rotating bands in $^{192}$Hg,
$^{194}$Hg and $^{194}$Pb obtained without including a treatment of pairing
correlations. Preliminary calculations are also presented with these
correlations included as well as an approximate projection on nucleon number.
Email contact: paul@amoco.saclay.cea.fr


title: Width of the $\Delta$ resonance in nuclei

abstract:
  In this work we evaluate the imaginary part of the isobar $\Delta$
self-energy $\Sigma_{\Delta}$ from the two-body absorption process
$\Delta+N\rightarrow 2N$. This contribution is calculated using a recently
developed non-relativistic scheme, which allows for an evaluation of the
self-energy with a basis of single-particle states appropriate for both bound
hole states and for particle states in the continuum. In order to test the
medium dependence of the self-energy, we calculate the two-body absorption term
$\Sigma_{\Delta}^{A2}$ for several finite nuclei with $N=Z$, i.e.\ $^{16}$O,
$^{40}$Ca and $^{100}$Sn. The resulting self-energy, which is energy dependent
and non-local, is compared with a simple parameterization derived from nuclear
matter.


title:
Perturbation schemes for systems of nucleons and pions: The relationship
  of covariant perturbation theory, the convolution integral and time-ordered
  perturbation theory

abstract:
  This paper is the first in a series of three which attempt to resolve the
difficulties that have plagued the $NN-\pi NN$ problem for the past ten years.
Various theoretical inconsistencies in the current formulation have been
pointed out and this work aims to eliminate these inconsistencies and so, we
hope, produce agreement with experiment. This is to be done by using covariant
perturbation theory, in which these inconsistencies are not present. The
covariant perturbation theory is developed starting from a model Lagrangian, in
order to fix notation and phases. It is shown that both old-fashioned
"time-ordered" perturbation theory and the convolution integral of Kvinikhidze
and Blankleider may be recovered from the covariant perturbation theory when
certain approximations are made. The connection of these results with the work
of Klein, L\'evy, Macke and Kadyshevsky is discussed. Two forthcoming papers
will pursue this covariant calculation in the $NN-\pi NN$ system using the
model and perturbation scheme developed in this paper and derive fully
covariant $NN-\pi NN$ equations without the double counting problems present in
previous covariant equations.


title: Neutron star properties from modern meson-exchange potential models

abstract:
  We calculate the total mass, radius, moment of inertia and surface
gravitational redshift for neutron stars using various equations of state. The
latter are derived from recent meson-exchange potential models, employing both
a relativistic and a non-relativistic Brueckner-Hartree-Fock approach.


title: Vector Color Transparency

abstract:
  Color transparency (CT) in high momentum transfer $(e,e' \vec p)$ reactions
is explored. The spin of the proton and photon are treated explicitly, hence
the name ``Vector CT". The Dirac distorted wave impulse approximation is used
as a starting point; then CT effects are embedded. A hadronic basis is used to
describe the struck proton as a wavepacket of physical baryon resonances. The
effects of the wavepacket expansion on the normal component of the ejectile
polarization, which vanishes in the limit of full CT, are investigated. This
formalism is also applied to study CT effects in total cross sections,
individual separated nuclear response functions, Fermi motion of the initial
nucleon, non-zero size of the initial wavepacket and the effects of
relativistic lower components. We show that including CT reduces the violations
of current conservation (CC), a typical problem in calculations of this kind.
The energy dependence of the normal polarization in $(e,e' \vec p)$ reactions
is found to be slow. However, a measurement of the normal transverse response
in a heavy nucleus, such as $^{208}Pb$ seems to afford the opportunity to see
CT at quite low momentum transfers. The effects of Fermi motion are
investigated, and choosing the momentum of the struck nucleon to be large leads
to significant violations of CC.


title: Symmetry properties of SU3 vector coupling coefficients

abstract:
  A presentation of the problem of calculating the vector coupling coefficients
for $SU3 \supset SU2 \otimes U1$ is made, in the spirit of traditional
treatments of SU2 coupling. The coefficients are defined as the overlap matrix
element between product states and a coupled state with good SU3 quantum
numbers. A technique for resolution of the outer degeneracy problem, based upon
actions of the infinitesimal generators of SU3 is developed, which
automatically produces vector coupling coefficients with symmetries under
exchange of state labels which parallel the familiar symmetries of the SU2
case. An algorithm for efficient computation of these coefficients is outlined,
for which an ANSI C code is available.


title:
Microscopic description of the beta delayed deuteron emission from
  \bbox{^6}He

abstract:
  The beta delayed deuteron emission from $^6$He is studied in a dynamical
microscopic cluster model. This model gives a reasonably good description for
all the subsystems of $^6$He and $^6$Li in a coherent way, without any free
parameter. The beta decay transition probability to the $^6$Li ground state is
underestimated by a few percents. The theoretical beta delayed deuteron
spectrum is close to experiment but it is also underestimated by about a factor
1.7. We argue that, in spite of their different magnitudes, both
underestimations might have a common origin. The model confirms that the
neutron halo part of the $^6$He wave function plays a crucial role in quenching
the beta decay toward the $\alpha$ + d channel.


title:
Combinatorial Study of Nuclear Level Density for Astrophysical
  Applications

abstract:
  We present some results and remarks based on a combinatorial approach of the
evaluation of the nuclear level density. First, we show that it is possible to
extract some reliable information from the output of the program whose rough
data present a strong statistical fluctuation from bin to bin. This includes
smoothing and evaluation of the desired quantities. After some comments about
the spin and parity distributions, we consider the question of the
non-equipartition of parities, mainly, at low energies. Finally, we present a
simple model to include and test this effect in the computation of
thermonuclear reaction rates.


title: Electromagnetic Currents and the Blankenbecler-Sugar Equation

abstract:
  The effective electromagnetic current density for a two-nucleon system that
is described by the Blankenbecler-Sugar equation is derived. In addition to the
single nucleon currents there are exchange currents of two different origins.
The first is the exchange current that is required to compensate for the
violation of the continuity equation in the impulse approximation. The second
is an exchange current, which arises in the quasipotential reduction from the
Bethe-Salpeter equation, and which represents effects of suppressed degrees of
freedom. Explicit general expressions are given for both of these exchange
currents. The results are applicable to both elastic and inelastic processes.


title: Shell model Monte Carlo calculations for Dy-170

abstract:
  We present the first auxiliary field Monte Carlo calculations for a rare
earth nucleus, Dy-170. A pairing plus quadrupole Hamiltonian is used to
demonstrate the physical properties that can be studied in this region. We
calculate various static observables for both uncranked and cranked systems and
show how the shape distribution evolves with temperature. We also introduce a
discretization of the path integral that allows a more efficient Monte Carlo
sampling.


title:
Applications of a Global Nuclear-Structure Model to Studies of the
  Heaviest Elements

abstract:
  We present some new results on heavy-element nuclear-structure properties
calculated on the basis of the finite-range droplet model and folded-Yukawa
single-particle potential. Specifically, we discuss calculations of nuclear
ground-state masses and microscopic corrections, $\alpha$-decay properties,
$\beta$-decay properties, fission potential-energy surfaces, and
spontaneous-fission half-lives. These results, obtained in a global
nuclear-structure approach, are particularly reliable for describing the
stability properties of the heaviest elements.


title: NN Correlations and Relativistic Hartree Fock in Finite Nuclei

abstract:
  Two different approximation schemes for the self-consistent solution of the
relativistic Brueckner-Hartree-Fock equation for finite nuclei are discussed
using realistic One-Boson-Exchange potentials. In a first scheme, the effects
of correlations are deduced from a study of nuclear matter and parameterized in
terms of an effective $\sigma$, $\omega$ and $\pi$ exchange. Employing this
effective interaction relativistic Hartree-Fock equations are solved for finite
nuclei \osi , \caf\ and \cafe . In the second approach the effect of
correlations are treated in the Brueckner-Hartree-Fock approximation directly
for the finite nuclei, but the modifications of the Dirac spinors in the medium
are derived from nuclear matter assuming a local-density approximation. Both
approaches yield rather similar results for binding energies and radii in fair
agreement with experimental data. The importance of the density dependent
correlation effects is demonstrated and different ingredients to the spin-orbit
splitting in the shell-model of the nucleus are discussed.


title:
Manifestation of Infrared Instabilities in High-Energy Processes in
  Nonabelian Gauge Theories

abstract:
  We show that a high frequency standing wave in SU(2) gauge theory is unstable
against decay into long wavelength modes. This provides a non-perturbative
mechanism for energy transfer from initial high momentum modes to final states
with low momentum excitations. The abelian case does not manifest such
instability. Our analysis is supported by lattice simulations.


title:
General Behavior of Double Beta Decay Amplitudes in the Quasiparticle
  Random Phase Approximation

abstract:
  Simple formulae for the $0^+\to 0^+$ double beta decay matrix elements, as a
function of the particle-particle strength $g^{pp}$, have been designed within
the quasiparticle random phase approximation. The $2\nu$ amplitude is a
bilinear function of $g^{pp}$, and all $0\nu$ moments behave as ratios of a
linear function and the square root of another linear function of $g^{pp}$. It
is suggested that these results are of general validity and that any
modifications of the nuclear hamiltonian or the configuration space cannot lead
to a different functional dependence.


title: Experimental Nuclear Masses and the Ground State of Cold Dense Matter

abstract:
  We study the consequences of recent progress in the experimental
determination of masses of neutron rich nuclei for our knowledge of the ground
state of cold dense matter. The most recent experimental data determine the
ground state of cold dense matter up to $ \rho \simeq 10^{11}~{\rm g~cm^{-3}}
$. The composition and the equation of state of the ground state of matter, in
this density interval, are calculated.


title:
Spectroscopic Factors in $^{40}$Ca and $^{208}$Pb from $(e,e'p)$: Fully
  Relativistic Analysis

abstract:
  We present results for spectroscopic factors of the outermost shells in
$^{40}$Ca and $^{208}$Pb, which have been derived from the comparison between
the available quasielastic ($e,e'p$) data from NIKHEF-K and the corresponding
calculated cross-sections obtained within a fully relativistic formalism. We
include exactly the effect of Coulomb distortion on the electron wave functions
and discuss its role in the extraction of the spectroscopic factors from
experiment. Without any adjustable parameter, we find spectroscopic factors of
about 70\%, consistent with theoretical predictions. We compare our results
with previous relativistic and nonrelativistic analyses of ($e,e'p$) data. In
addition to Coulomb distortion effects we discuss different choices of the
nucleon current operator and also analyze the effects due to the relativistic
treatment of the outgoing-distorted and bound nucleon wave functions.


title: Nuclear Shadowing at Small x and Q^2

abstract:
  Shadowing corrections to structure functions of heavy nuclei are calculated
at very low values of Bjorken-$x$ and at values of the momentum transfer
relevant to recent experiments. Good agreement is obtained with data from the
E665 Collaboration for Xe/D and Pb/D, and with the NMC data on Ca/D and C/D
structure function ratios. Corrections to the deuteron structure function are
also estimated down to $x \sim 10^{-5}$, and found to be less than about $3\%$
over the range of $x$ covered by the E665 data.


title: In-medium relativistic kinetic theory and nucleon-meson systems

abstract:
  Within the $\sigma-\omega$ model of coupled nucleon-meson systems, a
generalized relativistic Lenard--Balescu--equation is presented resulting from
a relativistic random phase approximation (RRPA). This provides a systematic
derivation of relativistic transport equations in the frame of nonequilibrium
Green's function technique including medium effects as well as flucuation
effects. It contains all possible processes due to one meson exchange and
special attention is kept to the off--shell character of the particles. As a
new feature of many particle effects, processes are possible which can be
interpreted as particle creation and annihilation due to in-medium one meson
exchange. In-medium cross sections are obtained from the generalized derivation
of collision integrals, which possess complete crossing symmetries.


title: The structure of the neutron deficient Sn isotopes

abstract:
  We calculate the spectra for the neutron deficient Sn isotopes with mass
numbers from A=102 to A=108, using standard many-body techniques. The G-matrix
used in the perturbative expansion was calculated using the Bonn potentials. A
good agreement with the available data is obtained.


title: The high-frequency finite-temperature quark dispersion relation

abstract:
  I calculate the dispersion relation for quarks of mass $m$ and momentum $k$
in a quark gluon plasma at temperature $T$, in the limit $m^2+k^2 \gg (gT)^2$,
where $g$ is the strong coupling constant. I find three contributions to the
dispersion relation: one that depends on $T$ but not $m$ or $k$, one that
depends on $m$ and $T$ but not $k$, and third contribution that depends on all
three (and is opposite in sign to the other two).


title: Anomaly in the charge radii of Pb isotopes

abstract:
  The anomalous behaviour of the charge radii of the isotopic chain of Pb
nuclei has been studied in the relativistic mean field theory. It has been
shown that the relativistic mean field provides an excellent description of the
anomalous kink in the isotopic shifts about $^{208}$Pb. This contrasts strongly
from the Skyrme mean field, where almost all the known and realistic forces
fail to reproduce the observed trend in the empirical data on the charge radii.
The results have been discussed in the perspective of differences in the
ans\"atze of the relativistic and the Skyrme mean-field theories.


title: Shape-Independent Expansion for the $^3S_1-^3D_1$ Mixing Parameter

abstract:
  A low-energy shape-independent expansion is suggested for the function
$[tan(2\epsilon_{BB})/(2k^2)]$, where $\epsilon_{BB}$ is the Blatt-Biedenharn
mixing parameter for the $^3S_1 -$ $^3D_1$ channel. This expansion allows an
evaluation of the mixing parameter $\epsilon_{BB}$ from a knowledge of the
deuteron asymptotic $D$ to $S$ ratio, pion mass and other low-energy
observables, such as the scattering lengths, deuteron binding etc., of the
nucleon-nucleon system. We demonstrate that the correct long range behavior of
the tensor potential is essential for a realistic reproduction of
$\epsilon_{BB}$.


title: Long-Range Correlations in Closed Shell Nuclei

abstract:
  The effects of correlations on the bulk properties of nuclei are investigated
in large model spaces including up to 21 single-particle orbits. The evaluation
of the single-particle Green function is made feasible by means of the BAGEL
approximation. The spectral function for single-nucleon pick-up and removal is
investigated for the nuclei $^{16}O$ and $^{40}Ca$ . Special attention is paid
to the effects produced by correlations on the calculated ground state
properties of closed shell nuclei. It is observed that correlations beyond the
Brueckner Hartree Fock approximation tend to improve the results obtained using
realistic nucleon nucleon interactions.


title:
Asymmetry of the Missing Momentum Distribution in (e,e$'$p) Reactions
  and Color Trnasparency

abstract:
  We suggest the measurement of the integrated asymmetry of teh missing
momentum distribution in (e,e$'$p)reactions to check color transparency effects
at intermediate momentum transfers.


title: Convergence properties of the effective interaction

abstract:
  The convergence properties of two perturbative schemes to sum the so-called
folded diagrams are critically reviewed, with an emphasis on the intruder state
problem. The methods we study are the approaches of Kuo and co-workers and Lee
and Suzuki. The suitability of the two schemes for shell-model calculations are
discussed.


title: Neutrino-Nucleus Reactions

abstract: Neutrino-nucleus reactions as applied to astrophysics are reviewed.


title:
Quasi-Elastic $d(\vec{p},\vec{n})2p$ Reaction and Spin Response
  Functions of the Deuteron

abstract:
  We calculated response functions of the deuteron for charge exchange
processes, including the final state interaction between two protons. Using
them we evaluated the double differential cross section and polarization
observables of $d(\vec{p},\vec{n})2p$ by means of plane wave impulse
approximation with an optimal factorization. Calculation well reproduced the
shape of the energy spectra of the cross section, though somewhat overestimated
the magnitude. It also reproduced the spin observables well.


title: Alpha Clustering and the stellar nucleosynthesis of carbon

abstract:
  The astrophysical S--factor and reaction rates for the triple--alpha process
are calculated in the direct--capture model. It is shown that the stellar
carbon production is extremely sensitive to small variations in the N--N
interaction.


title:
Properties of $^{8}$Be and $^{12}$C deduced from the folding--potential
  model

abstract:
  The $\alpha$--$\alpha$ differential cross sections are analyzed in the
optical model using a double--folded potential. With the knowledge of this
potential bound and resonance--state properties of $\alpha$--cluster states in
$^{8}$Be and $^{12}$C as well as astrophysical S--factors of
$^{4}$He($\alpha$,$\gamma$)$^{8}$Be and $^{8}$Be($\alpha$,$\gamma$)$^{12}$C are
calculated. $\Gamma_{\gamma}$--widths and B(E2)--values are deduced.


title:
Compatibility of Correlation Dynamics of SU(N) Gauge Theories and Gauss
  Law in Temporal Gauge

abstract:
  A constraint correlation dynamics up to 4-point Green's functions is proposed
for SU(N) gauge theories which reduces the N-body quantum field problem to the
two-body level. The resulting set of nonlinear coupled equations fulfills all
conservation laws including baryon number, linear and angular momenta as well
as the total energy. Apart from the conservation laws in the space-time degrees
of freedom the Gauss law is conserved identically for all times. The constraint
dynamical equations are highly non-perturbative and thus applicable also in the
strong coupling regime as e.g., low-energy QCD problems.


title:
Simultaneous Microscopic Description of 16O(gamma,n) and 16O(gamma,p)
  Including Delta Degrees of Freedom

abstract:
  The photonuclear reactions 16O(gamma,n)15O and 16O(gamma,p)15N are
simultaneously described within a coupled channels framework based on a
continuum shell model formulation. The inclusion of Delta(1232) isobar degrees
of freedom improves the description of the available data, however, complete
quantitative agreement is still lacking.


title: Identical Bands in Superdeformed Nuclei: A Relativistic Description

abstract:
  Relativistic Mean Field Theory in the rotating frame is used to describe
superdeformed nuclei. Nuclear currents and the resulting spatial components of
the vector meson fields are fully taken into account. Identical bands in
neighboring Rare Earth nuclei are investigated and excellent agreement with
recent experimental data is observed.


title:
Minijet-associated Dilepton Production in Ultrarelativistic Heavy Ion
  Collisions

abstract:
  Dilepton production associated with minijets is calculated in
ultrarelativistic heavy ion collisions using the first order approximation of
the dilepton fragmentation functions of quarks and gluons. The full QCD
evolution of the fragmentation functions is also studied. We find that the
dilepton pairs from the fragmentation of minijets are comparable to direct
Drell-Yan at $\sqrt{s}=200$ AGeV for small dilepton invariant mass $M\sim$ 1-2
GeV/c$^2$ while dominant over a large range of mass at $\sqrt{s}=6400$ AGeV.


title:
Calculating Dilepton Rates from Monte Carlo Simulations of Parton
  Production

abstract:
  To calculate dilepton rates in a Monte Carlo simulation of ultrarelativistic
heavy ion collisions, one usually scales the number of similar QCD processes by
a ratio of the corresponding differential probabilities. We derive the formula
for such a ratio especially for dilepton bremsstrahlung processes. We also
discuss the non-triviality of including higher order corrections to direct
Drell-Yan process. The resultant mass spectra from our Monte Carlo simulation
are consistent with the semi-analytical calculation using dilepton
fragmentation functions.


title: Quasiparticle properties and the dynamics of high-density nuclear matter

abstract:
  The energy spectrum of nucleons in high-density nuclear matter is
investigated in the framework of relativistic meson-nucleon many-body theory,
employing the $1/N$ expansion method. The coupling of the nucleon with the
particle-hole excitations in the medium flattens the spectra in the vicinity of
the Fermi surface. The effect grows logarithmically for increasing density and
eventually leads to instability of the normal state. The validity of the
mean-field theory at high density is criticized.


title:
Relations Between Isoscalar Charge Form Factors of Two- and
  Three-Nucleon Systems

abstract:
  Theoretical predictions for the deuteron and the isoscalar trinucleon charge
form factors are compared. Correlations between them are found. Linear
relations hold for the position of the diffraction minimum and for the position
and height of the secondary maximum. The linear relation for the diffraction
minimum misses the experimental data.


title:
Coexistence of Regular Undamped Nuclear Dynamics with Intrinsic
  Chaoticity

abstract:
  We study the conditions under which the nucleons inside a deformed nucleus
can undergo chaotic motion. To do this we perform self-consistent calculations
in semiclassical approximation utilizing a multipole-multipole interaction of
the Bohr-Mottelson type for quadrupole and octupole deformations. For the case
of harmonic and non-harmonic static potentials, we find that both multipole
deformations lead to regular motion of the collective coordinate, the multipole
moment of deformation. However, despite this regular collective motion, we
observe chaotic single particle dynamics.


title:
Practical solution to the Monte Carlo sign problem: Realistic
  calculations of 54Fe

abstract:
  We present a practical solution to the "sign problem" in the auxiliary field
Monte Carlo approach to the nuclear shell model. The method is based on
extrapolation from a continuous family of problem-free Hamiltonians. To
demonstrate the resultant ability to treat large shell-model problems, we
present results for 54Fe in the full fp-shell basis using the Brown-Richter
interaction. We find the Gamow-Teller beta^+ strength to be quenched by 58%
relative to the single-particle estimate, in better agreement with experiment
than previous estimates based on truncated bases.


title: Multinucleon Mechanisms in ($\gamma$,N) and ($\gamma$,NN) Reactions

abstract:
  The similarities in the experimental indications for multinucleon mechanisms
in $(\gamma,p)$ and $(e,e'p)$ processes are pointed out. For both types of
reactions, the substantial role of two-nucleon emission processes for
transitions to high excitation energies in the residual nucleus is stressed. A
microscopic model for the calculation of the two-body knockout contributions to
the inclusive $(\gamma,N)$ reaction is presented. It is based on an
unfactorized formalism for the calculation of electromagnetically induced
two-nucleon emission cross sections. The model is shown to yield a reasonable
description of the overall behaviour of the $^{12}$C$(\gamma,p)$ and
$^{12}$C$(\gamma,n)$ data at high excitation energies in the residual nucleus.
In the calculations effects from non-resonant and resonant pion exchange
currents are included. Photoabsorption on these currents are predicted to
produce the major contributions to the exclusive $^{16}$O$(\gamma,n_0)^{15}$O
process at photonenergies above the pion threshold. Double differential cross
sections for photon induced $pp$ and $pn$ emission from $^{16}$O are calculated
and compared with the data.


title: An antiproton-proton partial wave analysis

abstract:
  Invited talk presented by the first author at the XIVth European Conference
of Few-Body Problems in Physics, Amsterdam, August 23-28, 1993


title:
Deep Inelastic Scattering of Polarized Electrons off Polarized $^3$HE:
  Nuclear Effects and the Neutron Spin Structure Function

abstract:
  Nuclear effects in Deep Inelastic Scattering of polarized electrons off
polarized $^3$He are analyzed in terms of a spin dependent spectral function
taking into account $S'$ and $D$ waves in $^3$He, as well as Fermi motion and
binding effects. A simple and reliable equation relating the neutron and $^3$He
spin structure functions is proposed.


title: Quasi-Two-Body Decays of Nonstrange Baryons

abstract:
  We examine the decays of nonstrange baryons to the final states $\Delta\pi$,
$N\rho$, $N\eta$, $N\eta^\prime$, $N\omega$, $N1/2^+(1440)\pi$, and
$\Delta3/2^+(1600)\pi$, in a relativized pair-creation($^3P_0$) model which has
been developed in a previous study of the $N\pi$ decays of the same baryon
states. As it is our goal to provide a guide for the possible discovery of new
baryon states at CEBAF and elsewhere, we examine the decays of resonances which
have already been seen in the partial-wave analyses, along with those of states
which are predicted by the quark model but which remain undiscovered. The level
of agreement between our calculation and the available widths from the
partial-wave analyses is encouraging.


title:
Projected Linear Response Theory for Charge-Exchange Excitations and
  Double Beta Decay

abstract:
  The projected random phase approximation (PRPA) for charge-exchange
excitations is derived from the time-dependent variational principle. Explicit
results for the unperturbed energies (including the self-energy corrections),
the PRPA matrices, and the transition matrix elements are presented. The effect
of the projection procedure on the two-neutrino $\beta\beta$ decay in $^{76}Ge$
is briefly discussed.


title: In-medium relativistic kinetic theory and nucleon-meson systems

abstract:
  Within the $\sigma-\omega$ model of coupled nucleon-meson systems, a
generalized relativistic Lenard--Balescu--equation is presented resulting from
a relativistic random phase approximation (RRPA). This provides a systematic
derivation of relativistic transport equations in the frame of nonequilibrium
Green's function technique including medium effects as well as fluctuation
effects. It contains all possible processes due to one meson exchange and
special attention is kept to the off--shell character of the particles. As a
new feature of many particle effects, processes are possible which can be
interpreted as particle creation and annihilation due to in-medium one meson
exchange. In-medium cross sections are obtained from the generalized derivation
of collision integrals, which possess complete crossing symmetries.


title:
Thermo Field Dynamics for Quantum Fields with Continuous Mass Spectrum
  applied to Nuclear Physics

abstract:
  Transport coefficients are obtained by incorporating a gauge principle into
thermo field dynamics of inhomogeneous systems. In contrast to previous
derivations, neither imaginary time arguments nor perturbation theory in powers
of a coupling constant are used in the calculation. Numerical values are
calculated for the pion component in hot nuclear matter.


title: Spectral asymmetries in nucleon sum rules at finite density

abstract:
  Apparent inconsistencies between different formulations of nucleon sum rules
at finite density are resolved through a proper accounting of asymmetries in
the spectral functions between positive- and negative-energy states.


title: Two pion bound states in a hot pion gas

abstract:
  The occurrence of poles in the $2\pi$ propagator in a hot pion medium is
studied. The domain of non--trivial solutions to the corresponding bosonic gap
equation is investigated as a function of the chemical potential and
temperature of the gas.


title:
E2 properties of nuclei far from stability and the proton-halo problem
  of 8B

abstract:
  E2 properties of A=6--10 nuclei, including those of nuclei far from
stability, are studied by a $(0+2)\hbar\omega$ shell-model calculation which
includes E2 core-polarization effects explicitly. The quadrupole moments and
the E2 transition strengths in A=6--10 nuclei are described quite well by the
present calculation. This result indicates that the relatively large value of
the quadrupole moment of $^8$B can be understood without introducing the
proton-halo in $^8$B. An interesting effect of the $2\hbar\omega$
core-polarization is found for effective charges used in the $0\hbar\omega$
shell model; although isoscalar effective-charges are almost constant as a
function of nucleus, appreciable variations are needed for isovector
effective-charges which play important roles in nuclei with high
isospin-values.


title: Medium Modification to the $\Omega$-Meson Mass in the Walecka Model

abstract:
  We calculate the effective mass of the $\omega$ meson in nuclear matter in a
relativistic random-phase approximation to the Walecka model. The dressing of
the meson propagator is driven by its coupling to particle-hole pairs and
nucleon-antinucleon ($N\bar{N}$) excitations. We report a reduction in the
$\omega$-meson mass of about 170~MeV at nuclear-matter saturation density. This
reduction arises from a competition between the density-dependent
(particle-hole) dressing of the propagator and vacuum polarization ($N\bar{N}$
pairs). While density-dependent effects lead to an increase in the mass
proportional to the classical plasma frequency, vacuum polarization leads to an
even larger reduction caused by the reduced effective nucleon mass in the
medium.


title:
Is Schr\"{o}dinger's Conjecture for the Hydrogen Atom Coherent States
  Attainable

abstract:
  We construct the most general SO(4,2) hydrogen atom coherent states which are
the counterpart of Schr\"{o}dinger's harmonic oscillator coherent states. We
show that these states cannot be localized and cannot follow the classical
orbits. Thus, Schr\"{o}dinger's conjecture for the hydrogen atom coherent
states is unattainable.


title:
Nuclear shell-model calculations for 6Li and 14N with different NN
  potentials

abstract:
  Two ``phase-shift equivalent'' local NN potentials with different
parametrizations, Reid93 and NijmII, which were found to give nearly identical
results for the triton by Friar et al, are shown to yield remarkably similar
results for 6Li and 14N in a (0+2)hw no-core space shell-model calculation. The
results are compared with those for the widely used Hamada-Johnson hard-core
and the original Reid soft-core potentials, which have larger deuteron D-state
percentages. The strong correlation between the tensor strength and the nuclear
binding energy is confirmed. However, many nuclear-structure properties seem to
be rather insensitive to the details of the NN potential and, therefore, cannot
be used to test various NN potentials. (Submitted to Phys. Rev. C on Nov. 9,
1993 as a Brief Report.)


title: Deep Inelastic Scattering from off-Shell Nucleons

abstract:
  We derive the general structure of the hadronic tensor required to describe
deep-inelastic scattering from an off-shell nucleon within a covariant
formalism. Of the large number of possible off-shell structure functions we
find that only three contribute in the Bjorken limit. In our approach the usual
ambiguities encountered when discussing problems related to off-shellness in
deep-inelastic scattering are not present. The formulation therefore provides a
clear framework within which one can discuss the various approximations and
assumptions which have been used in earlier work. As examples, we investigate
scattering from the deuteron, nuclear matter and dressed nucleons. The results
of the full calculation are compared with those where various aspects of the
off-shell structure are neglected, as well as with those of the convolution
model.


title: A Systematic Treatment of Triaxial Systems at High Spins. II

abstract:
  The BRST treatment of triaxial nuclei rotating at high spins, which had been
previously developed, is extended to relate states with neighboring values of
the angular momentum $I$. As a consequence, the irreducible multipole
transition operators can be unambiguously separated into their physical and
spurious components. As a by product, we give explicit expressions for the
operators associated with the Goldstone-Nambu modes in terms of the final
orthonormal set of physical and spurious modes.


title: Exact, finite, and Hermitian fermion-pair-to-boson mapping

abstract:
  We discuss a general, exact (in that matrix elements are preserved) mapping
of fermion pairs to bosons, and find a simple factorization of the boson
representation of fermion operators. This leads to boson Hamiltonians that are
Hermitian and finite, with no more than two-body operators if the fermion
Hamiltonian has at most two-body operators, and one-body boson transition
operators if the fermion transition operator is one-body.


title:
Deformed Gaussian Orthogonal Ensemble Analysis of the Interacting Boson
  Model

abstract:
  A Deformed Gaussian Orthogonal Ensemble (DGOE) which interpolates between the
Gaussian Orthogonal Ensemble and a Poissonian Ensemble is constructed. This new
ensemble is then applied to the analysis of the chaotic properties of the low
lying collective states of nuclei described by the Interacting Boson Model
(IBM). This model undergoes a transition order-chaos-order from the $SU(3)$
limit to the $O(6)$ limit. Our analysis shows that the quantum fluctuations of
the IBM Hamiltonian, both of the spectrum and the eigenvectors, follow the
expected behaviour predicted by the DGOE when one goes from one limit to the
other.


title: Constraints on the $\pi NN$ Coupling Constant from the $NN$ System

abstract:
  The sensitivity of the deuteron and of $pp$ scattering to the $\pi NN$ and
$\rho NN$ coupling constants is investigated systematically. We find that the
deuteron can be described about equally well with either {\it large $\pi$ and
$\rho$} or {\it small $\pi$ and $\rho$} coupling constants. However, $pp$
scattering clearly {\it requires} the strong $\rho$, but favors the weak $\pi$
(particularly, in $^3P_0$ at low energies). This apparent contradiction between
bound-state and scattering can be resolved by either assuming charge-dependent
$\pi NN$ coupling constants or by adding a heavy pion to the NN model. In both
cases, the neutral-pion coupling constant is small ($g^2_{\pi^0}/4\pi= 13.5$).


title: Electromagnetic Gauge Invariance of Chiral Hybrid Quark Models

abstract:
  In this work, we investigate the question, whether the conventional analysis
of the electromagnetic form factors of the nucleon, evaluated in the framework
of the cloudy bag model (CBM) or other chirally invariant hybrid quark models
utilizing the same philosophy, is gauge invariant. In order to address that
point, we first formulate the CBM in a style that resembles the technique of
loop integrals. Evaluating the self energy and the electromagnetic form factors
of the nucleon in that manner and comparing with the standard analysis where
nonrelativistic perturbation theory is used, allows us to show that our
approach is appropriate and to point out, what approximations are made in the
standard derivation of the model. {}From the form of those loop integrals, we
then show that additional diagrams are needed to preserve electromagnetic gauge
invariance and we assess the corresponding corrections.


title:
Semiclassical Analysis of the Supershell Effect in Reflection-Asymmetric
  Superdeformed Oscillator

abstract:
  An oscillatory pattern in the smoothed quantum spectrum, which is unique for
single-particle motions in a reflection-asymmetric superdeformed oscillator
potential, is investigated by means of the semiclassical theory of shell
structure. Clear correspondence between the oscillating components of the
smoothed level density and the classical periodic orbits is found. It is shown
that an interference effect between two families of the short periodic orbits,
called supershell effect, develops with increasing reflection-asymmetric
deformations. Possible origins of this enhancement phenomena as well as quantum
signatures of period-multipling bifurcations are discussed in connection with
stabilities of the classical periodic orbits.


title:
Inclusive Quasielastic and Deep Inelastic Scattering of Polarized
  Electrons by Polarized $^{3}$He}

abstract:
  A comprehensive treatement of the theoretical approach for describing nuclear
effects in inclusive scattering of polarized electrons by polarized $^3$He is
presented.


title:
Higher-shell corrections for systems with one and two valence nucleons:
  A spin-orbit and tensor interaction analysis

abstract:
  It is shown that when higher-shell admixtures are included for systems with
two valence particles or holes, there are effects which are quite different
from those for one-valence-nucleon systems. For example, for nuclei with one
valence particle or hole, there is no first-order correction for the magnetic
dipole moment or the Gamow-Teller transition amplitude. However for nuclei with
two valence particles or holes, one can get substantial corrections. The
effects of the tensor and spin-orbit interactions in core renormalization are
emphasized. We find that in 6Li, the spin-orbit interaction causes the
quadrupole moment of the J=1+ ground state to be positive, but the tensor
interaction causes it to be negative. The G-matrices derived from realistic
interactions are employed in these calculations.


title:
On Size and Shape of the Average Meson Fields in the Semibosonized Nambu
  & Jona-Lasinio Model

abstract:
  We consider a two-flavor Nambu \& Jona-Lasinio model in Hartree approximation
involving scalar-isoscalar and pseudoscalar-isovector quark-quark interactions.
Average meson fields are defined by minimizing the effective Euklidean action.
The fermionic part of the action, which contains the full Dirac sea, is
regularized within Schwinger's proper-time scheme. The meson fields are
restricted to the chiral circle and to hedgehog configurations. The only
parameter of the model is the constituent quark mass $M$ which simultaneously
controls the regularization. We evaluate meson and quark fields
self-consistently in dependence on the constituent quark mass. It is shown that
the self-consistent fields do practically not depend on the constituent quark
mass. This allows us to define a properly parameterized reference field which
for physically relevant constituent masses can be used as a good approximation
to the exactly calculated one. The reference field is chosen to have correct
behaviour for small and large radii. To test the agreement between
self-consistent and reference fields we calculate several observables like
nucleon energy, mean square radius, axial-vector constant and delta-nucleon
mass splitting in dependence on the constituent quark mass. The agreement is
found to be very well. Figures available on request.


title: Pion Properties in a Hot $\Pi N \Delta$ Gas

abstract:
  Based on a recent meson-exchange model for the vacuum $\pi\pi$ interaction we
compute selfconsistently the in-medium $\pi\pi$ scattering amplitude and pion
selfenergy in a hot $\pi N\Delta$ gas. The contributions to the pion selfenergy
are calculated from the $\pi\pi$ T-matrix as well as from p-wave interaction
with nucleons and thermally abundant $\Delta$'s. Results are presented for two
scenarios believed to be realized in the relativistic heavy ion collisions
performed at the GSI-SIS and the CERN-SpS. Possible implications for the
observed soft pion enhancement at both SIS and SpS are indicated.


title: Optical-Model Description of Time-Reversal Violation

abstract:
  A time-reversal-violating spin-correlation coefficient in the total cross
section for polarized neutrons incident on a tensor rank-2 polarized target is
calculated by assuming a time-reversal-noninvariant, parity-conserving
``five-fold" interaction in the neutron-nucleus optical potential. Results are
presented for the system $n + {^{165}{\rm Ho}}$ for neutron incident energies
covering the range 1--20 MeV. From existing experimental bounds, a strength of
$2 \pm 10$ keV is deduced for the real and imaginary parts of the five-fold
term, which implies an upper bound of order $10^{-4}$ on the relative $T$-odd
strength when compared to the central real optical potential.


title: Coherent Pion Radiation From Nucleon Antinucleon Annihilation

abstract:
  A unified picture of nucleon antinucleon annihilation into pions emerges from
a classical description of the pion wave produced in annihilation and the
subsequent quantization of that wave as a coherent state. When the constraints
of energy-momentum and iso-spin conservation are imposed on the coherent state,
the pion number distribution and charge ratios are found to be in excellent
agreement with experiment.


title: Rates for the reactions antiproton-proton --> pi phi and gamma phi

abstract:
  We study antiproton-proton annihilation at rest into $\pi\phi$ and
$\gamma\phi$. Rescattering by $\overline{K^*}K+K^*\overline{K}$ and
$\rho^{+}\rho^{-}$ for $\overline{p}p\rightarrow\pi\phi$ states is sizable, of
order $(0.90\, {\rm to}\,2.6)\times 10^{-4}$ in the branching ratio, but
smaller than experiment. For $\overline{p}p\rightarrow\gamma\phi$ the
rescattering contributions are negligible, but the $\gamma\phi$ channel is well
explained by a $\rho\phi$ intermediate state combined with vector meson
dominance.


title: Three-body resonances by complex scaling

abstract:
  It is demonstrated that the complex scaling method can be used in practical
calculations to localize three-body resonances. Our model example emphasizes
the fact that in three-body systems several essentially different asymptotic
behaviors can appear. We show that the possibility of these different
asymptotic configurations can lead to an apparent, resonance like structure in
the three-body continuum.


title:
Dilepton production from virtual bremsstrahlung induced by proton
  capture

abstract:
  Dilepton production following radiative capture of a proton on a nuclear
target is studied in the Impulse Approximation. The cross section is decomposed
in terms of four time-like nuclear structure functions through a
longitudinal-transverse separation of the nuclear current. Using a simple PWIA
model, cross sections and conversion factors are calculated for capture
reactions p + n >> d + e^+ e^-, p + p >> 2He + e^+ e^- and p + 11B >> 12C + e^+
e^- at proton energies of 100-200 MeV. The result is compared with a recent
measurement of the conversion factor for p + 11B.


title: Chaotic Dynamics in the Framework of the Vlasov-Nordheim Equation

abstract:
  In the framework of the time-dependent mean field theory, we solve the
Vlasov-Nordheim equation and study the sensitive dependence of this highly
non-linear equation on the initial conditions. We find that, when nuclear
matter is inside the spinodal region, initially small differences between
similar trajectories grow exponentially and produce strongly divergent paths
resulting in a chaotic evolution. We focus on the fact that chaos spontaneously
arises without putting any additional noise. We calculate the largest Lyapunov
exponent for various initial densities. This analysis is performed for nuclear
matter in two dimensions. It is argued that the mean field chaoticity can cause
nuclear multifragmentation observed in intermediate energy heavy-ion reactions.


title:
Nuclear Polarization Corrections for the S--Levels of Electronic and
  Muonic Deuterium

abstract:
  We calculate the second-order corrections to the atomic energy level shifts
in ordinary and muonic deuterium due to virtual excitations of the deuteron
which are important for ongoing and planned precise experiments in these
systems. For light atoms a method can be used in which the shift is expressed
as integrals over the longitudinal and transverse inelastic structure functions
of the nucleus. We employ the structure functions arising from separable NN
potentials of the Yamaguchi and Tabakin form which can be evaluated
analytically. Special emphasis is put on gauge invariance which requires a
consistent inclusion of interaction currents and seagull terms. The effect of
the D-wave component of the deuteron is investigated for the leading
longitudinal contribution. We also estimate the shift for pionic deuterium.


title: Nuclear Charge Radii and Electric Quadrupole Moments

abstract:
  Isotope shifts of the mean square radii (MSR) and electric quadrupole moments
of even-even nuclei with 20< Z < 98$ are calculated using a dynamical
microscopic model. A single particle Nilsson potential with the Seo set of
correction term parameters, the pairing forces in the BCS formalism and a long
range interaction in the local approximation are used. A collective hamiltonian
is obtained using a generator coordinate method (GCM) with the gaussian overlap
approximation (GOA). A potential energy of the nucleus consists of a
microscopic-macroscopic Strutinsky energy and a zero point vibrational term. A
liquid droplet model is used as the macroscopic part of the potential. A BCS
wave function is taken as a generator function and two collective variables,
quadrupole and hexadecapole deformations, serve as the generator coordinates.


title:
Simple approximation for the starting-energy-independent two-body
  effective interaction with applications to 6Li

abstract:
  We apply the Lee-Suzuki iteration method to calculate the linked-folded
diagram series for a new Nijmegen local NN potential. We obtain an exact
starting-energy-independent effective two-body interaction for a multi-shell,
no-core, harmonic-oscillator model space. It is found that the resulting
effective-interaction matrix elements can be well approximated by the Brueckner
G-matrix elements evaluated at starting energies selected in a simple way.
These starting energies are closely related to the energies of the initial
two-particle states in the ladder diagrams. The ``exact'' and approximate
effective interactions are used to calculate the energy spectrum of 6Li in
order to test the utility of the approximate form.


title: Thermal quark production in ultra-relativistic nuclear collisions

abstract:
  We calculate thermal production of u, d, s, c and b quarks in
ultra-relativistic heavy ion collisions. The following processes are taken into
account: thermal gluon decay (g to ibar i), gluon fusion (g g to ibar i), and
quark-antiquark annihilation (jbar j to ibar i), where i and j represent quark
species. We use the thermal quark masses, $m_i^2(T)\simeq m_i^2 + (2g^2/9)T^2$,
in all the rates. At small mass ($m_i(T)<2T$), the production is largely
dominated by the thermal gluon decay channel. We obtain numerical and analytic
solutions of one-dimensional hydrodynamic expansion of an initially pure glue
plasma. Our results show that even in a quite optimistic scenario, all quarks
are far from chemical equilibrium throughout the expansion. Thermal production
of light quarks (u, d and s) is nearly independent of species. Heavy quark (c
and b) production is quite independent of the transition temperature and could
serve as a very good probe of the initial temperature. Thermal quark production
measurements could also be used to determine the gluon damping rate, or
equivalently the magnetic mass.


title: The classification of diagrams in perturbation theory

abstract:
  The derivation of scattering equations connecting the amplitudes obtained
from diagrammatic expansions is of interest in many branches of physics. One
method for deriving such equations is the classification-of-diagrams technique
of Taylor. However, as we shall explain in this paper, there are certain points
of Taylor's method which require clarification. Firstly, it is not clear
whether Taylor's original method is equivalent to the simpler
classification-of-diagrams scheme used by Thomas, Rinat, Afnan and Blankleider
(TRAB). Secondly, when the Taylor method is applied to certain problems in a
time-dependent perturbation theory it leads to the over-counting of some
diagrams. This paper first restates Taylor's method, in the process uncovering
reasons why certain diagrams might be double-counted in the Taylor method. It
then explores how far Taylor's method is equivalent to the simpler TRAB method.
Finally, it examines precisely why the double-counting occurs in Taylor's
method, and derives corrections which compensate for this double-counting.


title:
Slow proton production in deep-inelastic neutrino scattering on
  deuterium

abstract:
  The cross section for semi-inclusive deep inelastic charged current neutrino
scattering on hydrogen and deuterium in which a slow proton is observed in
coincidence with the muon is computed as a function of Bjorken x and light-cone
momentum of the detected proton. In the Impulse Approximation contributions
from hadronization and (in case of the deuteron) the emission of a spectator
nucleon are considered. In addition the probability for rescattering is
computed. The results are compared to a recent analysis of the data from the
WA25 (BEBC) experiment at CERN. (KVI-1024)


title: Microscopic analysis of two-body correlations in light nuclei

abstract:
  Within a nonperturbative dynamical two-body approach - based on coupled
equations of motion for the one-body density matrix and the two-body
correlation function - we study the distribution of occupation numbers in a
correlated system close to the groundstate, the relaxation of single-particle
excitations and the damping of collective modes. For this purpose the nonlinear
equations of motion are solved numerically within a finite oscillator basis for
the first time adopting short-range repulsive and long-range attractive
two-body forces. We find in all cases that the formation of long- and
short-range correlations and their mixing is related to the long- and
short-range part of the nucleon-nucleon interaction which dominate the
resummation of loop or ladder diagrams, respectively. However, the proper
description of relaxation or damping phenomena is found to require both types
of diagrams as well as the mixed terms simultaneously.


title: The $\pi \sigma$-Axial Exchange Current

abstract:
  The axial exchange current operator that arises from the coupling of the
axial field to the pion and effective scalar field in nuclei is constructed.
The spatial dependence of this exchange current operator may be determined
directly from the nucleon-nucleon interaction. This "$\pi\sigma$"-axial
exchange current contributes about 5\% to the quenching of the nucleon axial
current coupling constant $g_A^{GT}$ in heavy nuclei.


title: Shell Effects in Nuclei Near Neutron Drip

abstract:
  Shell effects in nuclei close to the neutron-drip lines have been
investigated. It has been demonstrated in the relativistic mean-field theory
that nuclei very far from stability manifest the shell effects strongly. This
behaviour is in accord with the predictions of nuclear masses in the
finite-range droplet model including shell corrections. As a consequence we
find a large neutron halo in nuclei near the neutron-drip line. The shell
effects predicted in the existing Skyrme mean-field theory in comparison are
significantly weaker than those of the other approaches.


title:
A Model Study of the Strength Distribution for a Collective State
  Coupled with Chaotic Background System

abstract:
  We consider a model in which a collective state couples to a large number of
background states. The background states can be chosen to have properties which
are classically characterized as regular or chaotic. We found that the
dynamical nature of the background system considerably affects some fluctuation
properties of the strength function. }


title:
Relativistic three-particle dynamical equations: I. Theoretical
  development

abstract:
  Starting from the two-particle Bethe-Salpeter equation in the ladder
approximation and integrating over the time component of momentum, we rederive
three dimensional scattering integral equations satisfying constraints of
relativistic unitarity and covariance, first derived by Weinberg and by
Blankenbecler and Sugar. These two-particle equations are shown to be related
by a transformation of variables. Hence we show how to perform and relate
identical dynamical calculation using these two equations. Similarly, starting
from the Bethe-Salpeter-Faddeev equation for the three-particle system and
integrating over the time component of momentum, we derive several three
dimensional three-particle scattering equations satisfying constraints of
relativistic unitarity and covariance. We relate two of these three-particle
equations by a transformation of variables as in the two-particle case. The
three-particle equations we derive are very practical and suitable for
performing relativistic scattering calculations.


title:
Polarization of the nuclear medium and RPA-type calculations in $K^+$
  scattering from nuclei

abstract:
  In the calculation of the $K^+$-nucleus cross sections, the coupling of the
mesons exchanged between the $K^+$ and the target nucleons to the polarization
of the Fermi sea has been taken into account. This polarization has been
calculated in the one-loop approximation but summed up to all orders (RPA-type
calculation). This effect is found to be rather important but does not improve
the agreement with experiment.


title:
Comment on "Phase-Shift Analysis of NN Scattering Below 160 Mev:
  Indication of a Strong Tensor Force"

abstract:
  In his recent publication of a NN phase shift analysis below 160 MeV, Henneck
reports relatively large values for the mixing parameter $\epsilon_1$. Based on
these results, Henneck suggests that the strength of the $\rho$-meson tensor
coupling to the nucleon may be weaker than used in present day NN interactions,
like the Paris or Bonn potentials. We point out that at low energies ( < 100
MeV ) there is very little sensitivity to the strength of the $\rho$ coupling,
due to the compensating effect of the second order tensor term. In order to
establish sensitivity, one has to go to energies > 200 MeV, where the second
order contribution has gone out. As it happens, the $\epsilon_1$ mixing
parameter is well determined in the region of energies 200--300 MeV, and there
is agreement with the predictions by the Paris and Bonn potentials; whereas the
weak-$\rho$ model is about 50\% above the data. This and additional
considerations in triplet $P$-waves re-confirm that NN scattering requires the
strong $\rho$, consistent with the $\pi\pi-N\bar{N}$ partial-wave analysis by
H\"ohler and Pietarinen.


title:
Relativistic three-particle dynamical equations: II. Application to the
  trinucleon system

abstract:
  We calculate the contribution of relativistic dynamics on the
neutron-deuteron scattering length and triton binding energy employing five
sets trinucleon potential models and four types of three-dimensional
relativistic three-body equations suggested in the preceding paper. The
relativistic correction to binding energy may vary a lot and even change sign
depending on the relativistic formulation employed. The deviations of these
observables from those obtained in nonrelativistic models follow the general
universal trend of deviations introduced by off- and on-shell variations of
two- and three-nucleon potentials in a nonrelativistic model calculation.
Consequently, it will be difficult to separate unambiguously the effect of off-
and on-shell variations of two- and three- nucleon potentials on low-energy
three-nucleon observables from the effect of relativistic dynamics.