title:
Ground state properties of exotic nuclei near Z=40 in the relativistic
  mean-field theory,

abstract:
  Study of the ground-state properties of Kr, Sr and Zr isotopes has been
performed in the framework of the relativistic mean field (RMF) theory using
the recently proposed relativistic parameter set NL-SH. It is shown that the
RMF theory provides an unified and excellent description of the binding
energies, isotope shifts and deformation properties of nuclei over a large
range of isospin in the Z=40 region. It is observed that the RMF theory with
the force NL-SH is able to describe the anomalous kinks in isotope shifts in Kr
and Sr nuclei, the problem which has hitherto remained unresolved. This is in
contrast with the density-dependent Skyrme Hartree-Fock approach which does not
reproduce the behaviour of the isotope shifts about shell closure. On the Zr
chain we predict that the isotope shifts exhibit a trend similar to that of the
Kr and Sr nuclei. The RMF theory also predicts shape coexistence in heavy Sr
isotopes. Several dramatic shape transitions in the isotopic chains are shown
to be a general feature of nuclei in this region. A comparison of the
properties with the available mass models shows that the results of the RMF
theory are generally in accord with the predictions of the finite-range droplet
model.


title: Short range correlations in the pion s-wave self-energy of pionic atoms

abstract:
  We evaluate the contribution of second order terms to the pion-nucleus s-wave
optical potential of pionic atoms generated by short range nuclear correlation.
The corrections are sizeable because they involve the isoscalar s-wave $\pi N$
amplitude for half off-shell situations where the amplitude is considerably
larger than the on-shell one. In addition, the s-wave optical potential is
reanalyzed by looking at all the different conventional contributions together
lowest order, Pauli corrected rescattering term, second order absorptive
effects, terms from the interaction of pions with the virtual pion cloud
(chiral corrections) and correlation effects. Different off-shell
extrapolations for the $\pi N$ amplitude are used and it is found that,
although some individual terms are sensitive to the extrapolation, the sum of
them is rather insensitive. The results are compared with empirical values from
best fits to the data and are found to be compatible, within theoretical and
empirical uncertainties. The results do not rule out further contributions but
they put stringent constraints on their strength.


title: Time reversal and parity breaking by propagation

abstract:
  The time independent mean field method (TIMF) for the calculation of matrix
elements of non relativistic propagators is based on a variational principle
whose non linearity induces a multiplicity of variational solutions. Several of
them can break any symmetry shared by the Hamiltonian and initial and final
states. We describe a soluble model where, in particular, time reversal and
parity breakings occur. Such breakings account for important properties of
propagation amplitudes.


title: Chiral Phase Structure of Hot and Dense Nuclear Matter

abstract:
  The description of nuclear matter bulk properties in the framework of
quark-based hadron models in curved unit cells is extended to finite
temperature. We discuss the analogy and interplay of density and temperature
effects in this formulation and study, as an application, the temperature and
density dependence of chiral vacuum properties in the Nambu-Jona-Lasinio (NJL)
model.


title: Efimov Effect Revisited with Inclusion of Distortions

abstract:
  An elementary proof of the 3-body Efimov effect is provided in the case of a
separable 2-body potential which binds at zero energy a light particle to a
heavy one. The proof proceeds by two steps, namely {\it i)} a projection of the
Hamiltonian in a subspace and the observation that the projected Hamiltonian
generates an arbitrarily large number of bound states, and {\it ii)} a use of
the Hylleraas-Undheim theorem to recover the unprojected Hamiltonian. The
definition of the projectors we use can include mean field distortions.


title: The Charge Response of a Meson-Correlated Relativistic Fermi Gas

abstract:
  The quasielastic longitudinal electromagnetic response function R_L is
studied within the context of a model that extends our previous investigations
of pionic correlations and currents. Four mesons are now employed (pion, rho,
sigma and omega, via the Bonn potential) and the many-body dynamics are
extended to the full random-phase approximation built upon a Hartree-Fock
basis. Wherever possible the Lorentz covariance of the problem is respected.
The first three energy-weighted moments of the reduced response are computed,
namely, the zeroth moment (Coulomb sum rule), the first moment (related to the
position of the quasielastic peak) and the second moment (related to the peak
width or variance). We discuss how with a modest downward adjustment of the
Fermi momentum it is possible to obtain the expected zeroth and second moments;
this implies that the nuclear system has a lower density than that required
when using the free relativistic Fermi gas and accordingly that the interaction
effects are weaker than one might initially find.


title:
Color Transparency Effects in Electron Deuteron Interactions at
  Intermediate Q^2

abstract:
  High momentum transfer electrodisintegration of polarized and unpolarized
deuterium targets, $d(e,e'p)n$ is studied. We show that the importance of final
state interactions-FSI, occuring when a knocked out nucleon interacts with the
other nucleon, depends strongly on the momentum of the spectator nucleon. In
particular, these FSI occur when the essential contributions to the scattering
amplitude arise from internucleon distances $\sim 1.5~fm$. But the absorption
of the high momentum $\gamma^*$ may produce a point like configuration, which
evolves with time. In this case, the final state interactions probe the point
like configuration at the early stage of its evolution. The result is that
significant color transparency effects, which can either enhance or suppress
computed cross sections, are predicted to occur for $\sim 4 GeV^2 \ge
Q^2\leq~10~(GeV/c)^2$.


title: Sensitivity of pp-Bremsstrahlung to Meson-Exchange Currents

abstract:
  We present pp-bremsstrahlung cross section calculations at the
$\pi$-production threshold to search for kinematics that best differentiate
model-dependent descriptions of the NN $t$-matrix and accentuate the
contributions of isoscalar meson-exchange currents. Existing optimization
procedures are shown to be completely unreliable due to the neglect of
meson-exchange currents and phase space variations. We show that phase-space
hides the most important differences in model $t$-matrices, but that improved
data will be critical to further investigations of exchange currents.


title:
pi N --> eta N and eta N --> eta N partial wave T-matrices in a coupled,
  three channel model

abstract:
  The pi N --> eta N and eta N --> eta N partial wave T-matrices for the eight
lowest partial waves have been obtained in a three coupled channel model with
unitarity manifestly imposed. The two physical channels are pi_N and eta_N, and
the third channel, pi_pi_N is an effective, but unphysical two body channel
which represents all remaining processes. The pi_N elastic phase shifts and the
weighted data base of the pi- p --> eta n total and differential cross sections
are chosen as the input for the fitting procedure. A model containing a single
resonance in each of the three partial waves that dominates the eta production
at lower energies is compared with previous analyses, based on similar
assumptions. A multiresonance coupled channel model is introduced which
significantly improves the agreement with all input data. Our results are
compared with a complementary multiresonance coupled channel analysis that is
constrained with elastic and continuum production channels. The inclusion of
the fourth P11 resonance in the 1440 - 2200 MeV region further improves the
agreement between the analysis and the data.


title: Propagation of a $K$-body force into $A$-body space

abstract:
  The calculation of the spreading width of a compound nuclear reaction caused
by a symmetry breaking $K$-body force acting in an $A$-body system ($K << A$,
usually $K=2$) involves the determination of the local average square matrix
element in $A$-body space. This problem is reduced to finding the global mean
square matrix element $v^2$ in $K$-body space. The result is a compact formula
for the spreading width which contains $v^2$ as an input. Our method is based
on the dilute gas approximation for excitons close to the Fermi edge. The
relative strength of the contributions of operators with different exciton rank
as well as the connection between the energy dependence of the spreading width
and the body rank of the underlying interaction are established.


title:
A unified description for nuclear equation of state and fragmentation in
  heavy ion collisions

abstract:
  We propose a model that provides a unified description of nuclear equation of
state and fragmentations. The equation of state is evaluated in Bragg-Williams
as well as in Bethe-Peierls approximations and compared with that in the mean
field theory with Skyrme interactions. The model shows a liquid-gas type phase
transition. The nuclear fragment distributions are studied for different
densities at finite temperatures. Power law behavior for fragments is observed
at critical point. The study of fragment distribution and the second moment
$S_2$ shows that the thermal critical point coincides with the percolation
point at the critical density. High temperature behavior of the model shows
characteristics of chemical equilibrium.


title:
A schematic model for fragmentation and phase transition in nuclear
  collisions

abstract:
  We develop here a simple yet versatile model for nuclear fragmentation in
heavy ion collisions. The model allows us to calculate thermodynamic properties
such as phase transitions as well as the distribution of fragments at
disassembly. In spite of its simplicity the model gives very good fit to recent
data taken at the Michigan National Superconducting Cyclotron Laboratory. The
model is an extension of a lattice gas model which itself has strong overlaps
with percolation models which have been used in the past to compare with
nuclear fragmentation data.


title:
Another Look at ``soft'' lepton pair production in nucleon-nucleon
  bremsstrahlung

abstract:
  We compare different formalisms for the calculation of lepton pair emission
in hadron-hadron collisions and discuss the consequences of the approximations
inherent to each of them. Using a Lorentz-covariant and gauge-invariant
formalism proposed by Lichard, we calculate lepton pair emission via
bremsstrahlung in proton-proton and neutron-proton reactions at energies
between 1 and 5 GeV to leading order in the virtual photon four-momentum. These
new results suggest that some previous bremsstrahlung calculations based on
varieties of the soft-photon approximation might have somewhat overestimated
the DLS low-mass dilepton cross sections. We find that the respective
intensities of dilepton production through $p p$ and $n p$ bremsstrahlung are
energy-dependent and become comparable at $E_{\rm kin} \agt $ 2 GeV. We also
calculate the polar angle anisotropy of the lepton spectrum.


title: Glauber theory of final-state interactions in $(e,e'p)$ scattering

abstract:
  We develop the Glauber theory description of final-state interaction (FSI) in
quasielastic $A(e,e'p)$ scattering. The important new effect is an interaction
between the two trajectories which enter the calculation of FSI-distorted
one-body density matrix and are connected with incoherent elastic rescatterings
of the struck proton on spectator nucleons. We demonstrate that FSI distortions
of the missing momentum distribution are large over the whole range of missing
momenta. Important finding is that incoherent elastic rescatterings of the
ejected proton lead to a strong quantum mechanical distortions of both the
longitudinal and transverse missing momentum distributions. It is shown that
allowance for finite longitudinal size of the interaction region for
proton-nucleon collision neglected in the standard Glauber model drastically
affects the theoretical predictions at high longitudinal missing momentum. We
also find very large corrections to the missing momentum distribution
calculated within the local-density approximation.


title:
Quadrupole deformation of deuterons and final state interaction in $^2
  \vec H (e,e'p)$ scattering on tensor polarized deuterons at CEBAF energies

abstract:
  The strength of final state interaction (FSI) between struck proton and
spectator neutron in $^2\vec{H}(e,e'p)$ scattering depends on the alignment of
the deuteron. We study the resulting FSI effects in the tensor analyzing power
in detail and find substantial FSI effects starting at still low missing
momentum $p_m \gsim 0.9 fm^{-1}$. At larger $p_m \gsim 1.5 fm^{-1}$, FSI
completely dominates both missing momentum distribution and tensor analyzing
power. We find that to a large extent FSI masks the sensitivity of the tensor
analyzing power to models of the deuteron wave function. For the transversely
polarized deuterons the FSI induced forward-backward asymmetry of the missing
momentum distribution is shown to have a node at precisely the same value of
$p_m$ as the PWIA missing momentum distribution. The position of this node is
not affected by FSI and can be a tool to distinguish experimentally between
different models for the deuteron wave function.


title: SOME ASPECTS OF ANTIPROTON--NUCLEUS PHYSICS

abstract:
  A brief review of antiproton--nucleus physics is presented. Some topics are
related to early LEAR experiments, and others to more recent measurements or
proposals. These include: exotic molecules, elastic and inelastic scattering,
  deep annihilation, strangeness production, neutron--antineutron oscillations,
halo nuclei, antiproton production in nuclear reactions etc.


title: Correlation Effects in Nuclear Transparency

abstract:
  The Glauber approximation is used to calculate the contribution of nucleon
correlations in high-energy $A(e,e'N)$ reactions. When the excitation energy of
the residual nucleus is small, the increase of the nuclear transparency due to
correlations between the struck nucleon and the other nucleons is mostly
compensated by a decrease of the transparency due to the correlations between
non detected nucleons. We derive Glauber model predictions for nuclear
transparency for the differential cross section when nuclear shell level
excitations are measured. The role of correlations in color transparency is
briefly discussed.


title: INCORPORATION OF QUANTUM STATISTICAL FEATURES IN MOLECULAR DYNAMICS

abstract:
  We formulate a method for incorporating quantum fluctuations into molecular-
dynamics simulations of many-body systems, such as those employed for energetic
nuclear collision processes. Based on Fermi's Golden Rule, we allow spontaneous
transitions to occur between the wave packets which are not energy eigenstates.
The ensuing diffusive evolution in the space of the wave packet parameters
exhibits appealing physical properties, including relaxation towards quantum-
statistical equilibrium.


title: Faddeev approach to the octet and decuplet baryons

abstract:
  A relativistic Faddeev model for the baryon octet is extended to treat the
baryon decuplet. We find that after determining the model parameters in the
mesonic sector the masses of both nucleon and delta deviate by less than 5\%
from the experimental data and show only a very weak dependence on the
constituent quark mass.


title: Meson Exchange Currents in Pion Double Charge Exchange at High Energies

abstract:
  In this letter we study the high energy behavior of the forward differential
cross section for the $^{18}O(\pi^+,\pi^-)^{18}Ne$ double charge exchange
reaction. We have evaluated the sequential and the meson exchange current
mechanisms. The meson exchange current contribution shows a very weak energy
dependence and becomes relevant at incident pion kinetic energies above 600
MeV.


title: Analysis of Boltzmann-Langevin Dynamics in Nuclear Matter

abstract:
  The Boltzmann-Langevin dynamics of harmonic modes in nuclear matter is
analyzed within linear-response theory, both with an elementary treatment and
by using the frequency-dependent response function. It is shown how the source
terms agitating the modes can be obtained from the basic BL correlation kernel
by a simple projection onto the associated dual basis states, which are
proportional to the RPA amplitudes and can be expressed explicitly. The source
terms for the correlated agitation of any two such modes can then be extracted
directly, without consideration of the other modes. This facilitates the
analysis of collective modes in unstable matter and makes it possible to asses
the accuracy of an approximate projection technique employed previously.


title:
Linking Dynamical and Thermal Models of Ultrarelativistic Nuclear
  Scattering

abstract:
  To analyse ultrarelativistic nuclear interactions, usually either dynamical
models like the string model are employed, or a thermal treatment based on
hadrons or quarks is applied. String models encounter problems due to high
string densities, thermal approaches are too simplistic considering only
average distributions, ignoring fluctuations. We propose a completely new
approach, providing a link between the two treatments, and avoiding their main
shortcomings: based on the string model, connected regions of high energy
density are identified for single events, such regions referred to as quark
matter droplets. Each individual droplet hadronizes instantaneously according
to the available n-body phase space. Due to the huge number of possible hadron
configurations, special Monte Carlo techniques have been developed to calculate
this disintegration.


title: The giant resonances in hot nuclei: linear response calculations

abstract:
  We calculate the isovector response function of hot nuclear matter using
various effective Skyrme interactions. For Skyrme forces with a small effective
mass the strength distribution is found to be nearly independent of
temperature, and shows little collective effects. In contrast effective forces
with an effective mass close to unity produce sizeable collective effects at
zero temperature which disappear at temperatures of a few MeV. We discuss the
relevance of these results for the saturation of the multiplicity of photons
emitted by the giant dipole resonance in hot nuclei beyond $T$=3 MeV observed
in recent experiments.


title:
Chiral anomaly and nucleon properties in the Nambu--Jona-Lasinio model
  with vector mesons

abstract:
  We consider the extended SU(3) Nambu and Jona-Lasinio model with explicit
vector couplings in the presence of external fields. We study the chiral
anomaly in this model and its implications on the properties of the nucleon
described as a chiral soliton of three valence quarks bounded in mesonic
background fields. For the model to reproduce the QCD anomaly it is necessary
to subtract suitable local and polynomial counterterms in the external and
dynamical vector and axial-vector fields. We compute the counterterms
explicitly in a vector gauge invariant regularization, and obtain modifications
to the total effective action and vector and axial currents. We study the
numerical influence of those counterterms in the two flavour version of model
with dynamical $\sigma,\pi, \rho, A $ and $\omega$ mesons. We find that, for
time independent hedgehog configurations, the numerical effects in the nucleon
mass, the isoscalar nucleon radius and the axial coupling constant are
negligibly small.


title:
An $U_{qp}(u_2)$ Rotor Model for Rotational Bands of Superdeformed
  Nuclei

abstract:
  A nonrigid rotor model is developed from the two-parameter quantum algebra
$U_{qp}({\rm u}_2)$. [This model presents the $U_{qp}({\rm u}_2)$ symmetry and
shall be referred to as the qp-rotor model.] A rotational energy formula as
well as a qp-deformation of E2 reduced transition probabilities are derived.
The qp-rotor model is applied (through fitting procedures) to twenty rotational
bands of superdeformed nuclei in the $A \sim 130$, 150 and 190 mass regions.
Systematic comparisons between the qp-rotor model and the q-rotor model of
Raychev, Roussev and Smirnov, on one hand, and a basic three-parameter model,
on the other hand, are performed on energy spectra, on dynamical moments of
inertia and on B(E2) values. The physical signification of the deformation
parameters q and p is discussed.


title: Pseudo-Spin Symmetry and its Applications

abstract:
  The pseudo-spin symmetry is reviewed. A mapping that produces the separation
of the total angular momentum into pseudo-orbital and pseudo-spin degrees of
freedom is discussed, together with the analytic transformations that take us
from the normal parity space to the eigenstates of a pseudo-oscillator with one
quanta less. The many-particle version of the unitary transformation to the
pseudo-SU(3) space is established. As an example, these symmetries are used to
describe the double beta decay phenomenon in heavy deformed nuclei.


title: Double beta decay to excited states in Nd150

abstract:
  The pseudo SU(3) model is used to study the double beta decay of Nd150 to the
ground and excited states of Sm150 . Low lying collective excitations of Sm150
and its BE(2) intensities are well reproduced. Expressions for the two neutrino
double beta decay to excited states are developed and used to describe the
decay of Nd150 . The existence of selection rules which strongly restrict the
decay is discussed.


title: Double beta decay in heavy deformed nuclei: what have we learned?

abstract:
  The pseudo SU(3) approach is used to describe low lying states and BE(2)
intensities of rare earth and actinide nuclei which are double beta decay
candidates. The double beta half lives of some of these nuclei to the ground
and excited states of the final ones are evaluated for both the two and zero
neutrino emitting modes. The existence of selection rules which strongly
restrict the decays is discussed. These restrictions represent a possible test
of the model. Up to now the predictions are in good agreement with the
available experimental data.


title: The Weak Parity-Violating Pion-Nucleon Coupling

abstract:
  We use QCD sum rules to obtain the weak parity-violating pion-nucleon
coupling constant $f_{\pi NN}$. We find that $f_{\pi NN}\approx 3\times
10^{-8}$, up to an order of magnitude smaller than the ``best estimates" based
on quark models. This result follows from the cancellation between perturbative
and nonperturbative QCD processes not found in quark models, but explicit in
the QCD sum rule method. Our result is consistent with the experimental upper
limit found from $^{18}$F parity-violating measurements.


title: Universality of Symmetry and Mixed-symmetry Collective Nuclear States

abstract:
  The global correlation in the observed variation with mass number of the $E2$
and summed $M1$ transition strengths is examined for rare earth nuclei. It is
shown that a theory of correlated $S$ and $D$ fermion pairs with a simple
pairing plus quadrupole interaction leads naturally to this universality. Thus
a unified and quantitative description emerges for low-lying quadrupole and
dipole strengths.


title: Instant Two-Body Equation in Breit Frame

abstract:
  A quasipotential formalism for elastic scattering from relativistic bound
states is based on applying an instant constraint to both initial and final
states in the Breit frame. This formalism is advantageous for the analysis of
electromagnetic interactions because current conservation and four momentum
conservation are realized within a three-dimensional formalism. Wave functions
are required in a frame where the total momentum is nonzero, which means that
the usual partial wave analysis is inapplicable. In this work, the
three-dimensional equation is solved numerically, taking into account the
relevant symmetries. A dynamical boost of the interaction also is needed for
the instant formalism, which in general requires that the boosted interaction
be defined as the solution of a four-dimensional equation. For the case of a
scalar separable interaction, this equation is solved and the Lorentz
invariance of the three-dimensional formulation using the boosted interaction
is verified. For more realistic interactions, a simple approximation is used to
characterize the boost of the interaction.


title: Meson-Exchange Currents in pp-Bremsstrahlung

abstract:
  The long-standing discrepancy between pp-bremsstrahlung data and calculations
based on the relativistic impulse approximation current is substantially
reduced by the inclusion of the PV$\gamma$ and intermediate-state
$\Delta$-resonance iso-scalar meson-exchange currents. The success of the
standard procedures adopted here shows that pp-bremsstrahlung provides a
powerful tool for the further study of $T$=1 isoscalar exchange currents. The
need for addition high-precision data is stressed.


title: Resolving Power of 2-D Pion Interferometry

abstract:
  A $\chi^2$ analysis is performed to test the resolving power of
two-dimensional pion interferometry using for illustration the preliminary E802
data on $Si+Au$ at 14.6 AGeV/c. We find that the resolving power to distinguish
two decoupling geometries of different dynamical models is enhanced by studying
the variation of the mean $\chi^2$ per degrees of freedom with respect to the
range of the analysis in the $q_T,q_L$ plane. The preliminary data seem to rule
out dynamical models with significant $\omega,\eta$ resonance formation yields.


title:
Nuclear Medium Effects in the Relativistic Treatment of Quasifree
  Electron Scattering

abstract:
  Non-relativistic reduction of the S-matrix for the quasifree electron
scattering process $A\left(~e, e'p~\right)A-1$ is studied in order to
understand the source of differences between non-relativistic and relativistic
models. We perform an effective Pauli reduction on the relativistic expression
for the S-matrix in the one-photon exchange approximation. The reduction is
applied to the nucleon current only; the electrons are treated fully
relativistically. An expansion of the amplitude results in a power series in
the nuclear potentials. The series is found to converge rapidly only if the
nuclear potentials are included in the nuclear current operator. The results
can be cast in a form which reproduces the non-relativistic amplitudes in the
limit that the potentials are removed from the nuclear current operator. Large
differences can be found between calculations which do and do not include the
nuclear potentials in the different orders of the nuclear current operator. In
the high missing momentum region we find that the non-relativistic calculations
with potentials included in the nuclear current up to second order give results
which are close to those of the fully relativistic calculation. This behavior
is an indication of the importance of the medium modifications of the nuclear
currents in this model, which are naturally built into the relativistic
treatment of the reaction.


title: High-energy scissors mode

abstract:
  All the orbital M1 excitations, at both low and high energies, obtained from
a rotationally invariant QRPA, represent the fragmented scissors mode. The
high-energy M1 strength is almost purely orbital and resides in the region of
the isovector giant quadrupole resonance. In heavy deformed nuclei the
high-energy scissors mode is strongly fragmented between 17 and 25 MeV (with
uncertainties arising from the poor knowledge of the isovector potential). The
coherent scissors motion is hindered by the fragmentation and $B(M1) < 0.25 \;
\mu^2_N$ for single transitions in this region. The $(e,e^{\prime})$ cross
sections for excitations above 17 MeV are one order of magnitude larger for E2
than for M1 excitations even at backward angles.


title:
Numerical Analyses of CERN 200GeV/A Heavy-Ion Collisions Based on a
  Hydrodynamical Model with Phase Transition

abstract:
  We numerically analyze recent high energy heavy-ion collision experiments
based on a hydrodynamical model with phase transition and discuss a systematic
change of initial state of QGP-fluid depending on colliding-nuclei's mass. In a
previous paper, we formulated a (3+1)-dimensional hydrodynamical model for
quark-gluon plasma with phase transition and discussed numerically the
space-time evolution in detail. We here compare the numerical solution with the
hadronic distributions given by CERN WA80 and NA35. Systematic analyses of the
experiments with various colliding nuclei enable us to discuss the dependences
of the initial parameters of the hydrodynamical model on colliding nuclei's
mass. Furthermore, extrapolating the present experiments, we derive the
possible hadronic distributions for lead-lead 150GeV/A collision.


title:
S-wave Meson-Nucleon Interactions and the Meson Mass in Nuclear Matter
  from Chiral Effective Lagrangians

abstract:
  Chiral effective lagrangians may differ in their prediction of meson-nucleon
scattering amplitudes off-meson-mass-shell, but must yield identical S-matrix
elements. We argue that the effective meson mass in nuclear matter obtained
from chiral effective lagrangians is also unique. Off-mass-shell amplitudes
obtained using the PCAC choice of pion field must therefore not be viewed as
fundamental constraints on the dynamics, the determination of the effective
meson mass in nuclear matter or the possible existence of meson condensates in
the ground state of nuclear matter. This hypothesis is borne out by a
calculation of the effective mass in two commonly employed formulations of
chiral perturbation theory which yield different meson-nucleon scattering
amplitudes off-meson-mass-shell.


title: On Neutrino Emission From Dense Matter Containing Meson Condensates

abstract:
  We consider the rate at which energy is emitted by neutrinos from the dense
interior of neutron stars containing a Bose condensate of pions or kaons. The
rates obtained are larger, by a factor of 2, than those found earlier, and are
consistent with those found for the direct Urca processes.


title:
Determination of the $\pi NN$ form factor from the threshold pion
  production of $pp$ scattering

abstract:
  It is shown that the threshold productions of $\pi^0 pp$, $\pi^+ np$ and
$\pi^+ d$ from $pp$ collisions can be consistently described by a model
consisting of a pion s-wave rescattering and $N\bar N$ pair-terms of
heavy-meson exchanges. The large difference between $\sigma^{tot}
(pp\rightarrow\pi ^+ d)$ and $\sigma^{tot} (pp\rightarrow\pi ^+ np)$ is
understood from the orthogonality of the deuteron and the $np$ scattering wave
functions. In a calculation using the Paris potential to account for the
initial and final $NN$ interactions, it is found that the data can be best
reproduced by using a soft $\pi NN$ form factor with $\Lambda_{\pi} =650 $ MeV
for a monopole form. This is consistent with an earlier study of pion
production in the $\Delta$ excitation region.


title:
Isospin Dependence of the Spin-Orbit Force and Effective Nuclear
  Potentials,

abstract:
  The isospin dependence of the spin-orbit potential is investigated for an
effective Skyrme-like energy functional suitable for density dependent
Hartree-Fock calculations. The magnitude of the isospin dependence is obtained
from a fit to experimental data on finite spherical nuclei. It is found to be
close to that of relativistic Hartree models. Consequently, the anomalous kink
in the isotope shifts of Pb nuclei is well reproduced.


title: The Disappearance of Flow

abstract:
  We investigate the disappearance of collective flow in the reaction plane in
heavy-ion collisions within a microscopic model (QMD). A systematic study of
the impact parameter dependence is performed for the system Ca+Ca. The balance
energy strongly increases with impact parameter. Momentum dependent
interactions reduce the balance energies for intermediate impact parameters
$b\approx4.5$ fm. Dynamical negative flow is not visible in the laboratory
frame but does exist in the contact frame for the heavy system Au+Au. For
semi-peripheral collisions of Ca+Ca with $b\approx6.5$ fm a new two-component
flow is discussed. Azimuthal distributions exhibit strong collectiv flow
signals, even at the balance energy.


title:
Variational calculations of the $\Lambda$-seperation energy of the
  $_{\Lambda}^{17}$O hypernucleus

abstract:
  Variational Monte Carlo calculations have been made for the $_{
\Lambda}^{17}$O hypernucleus using realistic two- and three-baryon
interactions. A two pion exchange potential with spin- and space-exchange
components is used for the $\Lambda$N potential. Three-body two-pion exchange
and strongly repulsive dispersive $\Lambda$NN interactions are also included.
The trial wave function is constructed from pair- and triplet-correlation
operators acting on a single particle determinant. These operators consist of
central, spin, isospin, tensor and three- baryon potential components. A
cluster Monte Carlo method is developed for noncentral correlations and is used
with up to four-baryon clusters in our calculations. The three-baryon
$\Lambda$NN force is discussed.


title:
Sensitivity of the nuclear equation of state towards relativistic
  effects

abstract:
  We analyze relativistic effects in transverse momentum using Quantum
Molecular Dynamics [QMD] and its covariant extension Relativistic Quantum
Molecular Dynamics [RQMD]. The strength of the relativistic effects is found to
increase with the bombarding energy and with an averaged impact parameter. The
variation in the intensity of the relativistic effects with variation in the
mass of the colliding nuclei is not systematic. Furthermore, the hard EOS is
affected drastically by the relativistic effects whereas the soft EOS is
affected less. Our analysis shows that up to the bombarding energy of 1
GeV/nucl., the influence of relativistic effects is small. Whereas at higher
energies, relativistic effects become naturally very important.


title:
Study of non-equilibrium effects and thermal properties of heavy ion
  collisions using a covariant approach

abstract:
  Non-equilibrium effects are studied using a full Lorentz-invariant formalism.
Our analysis shows that in reactions considered here, no global or local
equilibrium is reached. The heavier masses are found to be equilibrated more
than the lighter systems. The local temperature is extracted using hot Thomas
Fermi formalism generalized for the case of two interpenetrating pieces of
nuclear matter. The temperature is found to vary linearly with bombarding
energy and impact parameter whereas it is nearly independent of the mass of the
colliding nuclei. This indicates that the study of temperature with medium size
nuclei is also reliable. The maximum temperatures obtained in our approach are
in a nice agreement with earlier calculations of other approaches. A simple
parametrization of maximal temperature as a function of the bombarding energy
is also given.


title:
Consequences of a covariant Description of Heavy Ion Reactions at
  intermediate Energies

abstract:
  Heavy ion collisions at intermediate energies are studied by using a new RQMD
code, which is a covariant generalization of the QMD approach. We show that
this new implementation is able to produce the same results in the
nonrelativistic limit (i.e. 50MeV/nucl.) as the non-covariant QMD. Such a
comparison is not available in the literature. At higher energies (i.e. 1.5
GeV/nucl. and 2 GeV/nucl.) RQMD and QMD give different results in respect to
the time evolution of the phase space, for example for the directed transverse
flow. These differences show that consequences of a covariant description of
heavy ion reactions within the framework of RQMD are existing even at
intermediate energies.


title: Relativistic Effects in Heavy-Ion Collisions at SIS Energies

abstract:
  The covariant and non-covariant Quantum Molecular Dynamics models are applied
to investigate possible relativistic effects in heavy ion collisions at SIS
energies. These relativistic effects which arise due to the full covariant
treatment of the dynamics are studied at bombarding energies E$_{lab.}$ = 50,
250, 500, 750, 1000, 1250, 1500, 1750 and 2000 MeV/nucl.. A wide range of the
impact parameter from b = 0 fm to b = 10 fm is also considered. In the present
study, five systems $^{12}$C-$^{12}$C, $^{16}$O-$^{16}$O, $^{20}$Ne-$^{20}$Ne,
$^{28}$Si-$^{28}$Si and $^{40}$Ca-$^{40}$Ca are investigated. The full
covariant treatment at low energies shows quite good agreement with the
corresponding non-covariant approach whereas at higher energies it shows less
stopping and hence less thermal equilibrium as compared to the non-covariant
approach. The collisions dynamics is less affected. The density using RQMD
rises and drops faster than with QMD. The relativistic effects show some
influence on the resonance matter production. Overall, the relativistic effects
at SIS energies ($\leq$ 2000 MeV/nucl.) are less significant.


title: Up-Down Quark Mass Difference Effect in Nuclear Many-Body Systems

abstract:
  A charge-symmetry-breaking nucleon-nucleon force due to the up-down quark
mass difference is evaluated in the quark cluster model. It is applied to the
shell-model calculation for the isovector mass shifts of isospin multiplets and
the isospin-mixing matrix elements in 1s0d-shell nuclei. We find that the
contribution of the quark mass difference effect is large and agrees with
experiment. This contribution may explain the Okamoto-Nolen-Schiffer anomaly,
alternatively to the meson-mixing contribution, which is recently predicted to
be reduced by the large off-shell correction.


title:
Inverted Pairing and Excitation Induced by Quadrupole-Quadrupole
  Interaction

abstract:
  In this paper, eit is shown for a single-$j$ shell that the intrinsic
excitations induced by the quadrupole-quadrupole interaction can be viewed as
that due to the inverted surface-delta interaction whose multipole-pairing
component with the largest spin is the dominant term and is attractive. This
allow us to trace the origin of the recently introduced optimum pair
description of rotation and leads naturally to analytical expressions for the
rotational energies for the various bands in a single $j$-shell with the
quadrupole-quadrupole interaction.


title: Comment on "Role of heavy meson exchange in near threshold N N --> d pi"

abstract:
  In a recent paper by C. J. Horowitz (Phys. Rev. C {\bf 48}, 2920 (1993)) a
heavy meson exchange is incorporated into threshold NN --> d pi to enhance the
grossly underestimated cross section. However, that calculation uses an
unjustified assumption on the initial and final momenta, which causes an
overestimate of this effect by a factor of 3--4. I point out that the inclusion
of the Delta(1232) isobar increases the cross section significantly even at
threshold.


title:
Constraints on Coupling Constants through Charged $\Sigma$
  Photoproduction

abstract:
  The few available data for the reactions $\gamma p \rightarrow K^{0}
\Sigma^{+}$ and $\gamma n \rightarrow K^{+} \Sigma^{-}$ are compared to models
developed for the processes $\gamma p \rightarrow K^{+} \Sigma^{0}$ and $\gamma
p \rightarrow K^{+} \Lambda$. It is found that some of these phenomenological
models overpredict the measurements by up to a factor of 100. Fitting the data
for all of these reactions leads to drastically reduced Born coupling
constants.


title:
eta N S-wave scattering length in a three coupled channel,
  multiresonance, unitary model

abstract:
  The S-wave scattering length for eta-N elastic scattering is extracted from
the S-wave T-matrix in a three coupled channel, multiresonance unitary model.
Results are compared with values already reported in literature which are
obtained applying multichannel, but single resonance -- no background models. A
dispersion among the previously published values of the real part of the S-wave
scattering length is observed. We demonstrate that the reported spread
originates from the strong sensitivity of the scattering length upon the small
variation of the used input resonance parameters. In addition, we show that
eta-N scattering length value obtained in single resonance -- no background
models significantly increases if background term is added in a unitary way. We
question the reliability of previously reported values based only on the single
resonance -- no background models, and demonstrate that the value of the eta-N
S-wave scattering length obtained in this publication is much more realistic
because of the multiresonance and unitary approach.


title:
THE COUPLING OF THE $f_1(1285)$ MESON TO THE ISOSCALAR AXIAL CURRENT OF
  THE NUCLEON

abstract:
  The weak decay as well as the strong nucleon coupling constants of the
isoscalar axial vector meson $f_1 (1285)$ are estimated within the octet quark
model. It is shown that the empirical value for the coupling of $\overline{s}s$
quarkonium to nucleons can be understood by attributing the $f_1(1285)$-nucleon
coupling to the $a_0\pi N$ triangle diagram.


title: Probing the Ground State and Transition Densities of Halo Nuclei

abstract:
  We investigate the use of elastic and inelastic scatterings with secondary
beams of radioactive nuclei as a mean to obtain information on ground state
properties and transition matrix elements to continuum states. An eikonal model
is developed for this purpose by using the folding potential. In particular we
discuss possible signatures of halo wavefunctions in elastic and inelastic
scattering experiments.


title: The Photodissociation of $^8B$ and the Solar Neutrino Problem

abstract:
  The extraction of the photodissociation cross sections of $^8B$ from Coulomb
dissociation experiments is investigated. A careful study is done on the
contributions of the E1, E2 and M1 multipolarities to the breakup. A comparison
with the data of a recent experiment is performed. It is shown that the
extraction of the radiative capture cross sections $^7Be(p,\ \gamma)^8B$ which
are relevant for the solar neutrino problem is not affected appreciably by
Coulomb reacceleration. A non-perturbative model is used for the purpose.
Emphasis is put on the perspectives for future experiments which are planned at
the University of Notre Dame, RIKEN (Japan), and GSI (Germany). An analysis of
the total yields of ``photon-point" processes in inelastic electron scattering
is also done.


title:
HIJING 1.0: A Monte Carlo Program for Parton and Particle Production in
  High Energy Hadronic and Nuclear Collisions

abstract:
  Based on QCD-inspired models for multiple jets production, we developed a
Monte Carlo program to study jet and the associated particle production in high
energy $pp$, $pA$ and $AA$ collisions. The physics behind the program which
includes multiple minijet production, soft excitation, nuclear shadowing of
parton distribution functions and jet interaction in dense matter is briefly
discussed. A detailed description of the program and instructions on how to use
it are given.


title: Are there eta-Helium bound states?

abstract:
  Using multiple scattering theory the scattering lengths of $\eta$ mesons on
helium nuclei are calculated and checked against final state $\eta$
interactions from the $pd \rightarrow \eta ^3$He and $dd \rightarrow \eta ^4$He
reactions. The existence of an $\eta^4$He quasibound state is indicated.


title:
Thermal Properties of a Hot Pion Gas beyond the Quasiparticle
  Approximation

abstract:
  Within the Matsubara formalism we derive expressions for the pion self-energy
and the two-pion propagator in a hot pion gas. These quantities are used to
selfconsistently calculate the in-medium $\pi\pi$ amplitude beyond the
quasiparticle approximation (QPA). The results are shown to differ
significantly from QPA-based calculations. We also examine the impact of chiral
constraints on the $\pi\pi$ interaction in a chirally improved version of the
J\"ulich $\pi\pi$ model.


title:
WHAT DO WE LEARN FROM ATOMIC PHYSICS ABOUT FUNDAMENTAL SYMMETRIES IN
  NUCLEI AND PARTICLES

abstract:
  Atomic experiments bring meaningful and valuable information on fundamental
symmetries. The hypothesis of a large ($\sim 100$ eV) P-odd weak matrix element
between single-particle states in heavy nuclei is inconsistent with the results
of atomic PNC experiments. Upper limits on CP-violation obtained in atomic and
molecular spectroscopy are as informative as those established in neutron
physics. Very strict upper limits on T-odd, P-even interactions
(nucleon-nucleon, electron-nucleon, electron-electron, and $\beta$-decay) are
derived from the same atomic and neutron experiments.


title: REGULAR SUPPRESSION OF P,T-VIOLATING NUCLEAR MATRIX ELEMENTS

abstract:
  In heavy nuclei there is a parametrical suppression, $\;\sim A^{-1/3}\;$, of
T-odd, P-odd matrix elements as compared to T-even, P-odd ones.


title: Evidence for excess pions in nuclei

abstract:
  We analize two reactions: the electroproduction at small x and the Drell-Yan
production by protons on nuclei. We show that nuclear shadowing in
electroproduction is larger if the virtuality of inter- mediate hadrons is
properly taken into account. In the Drell-Yan production, initial state
interactions of fast partons are included. With this input, the excess pion
contribution improves the description of data for both reactions.


title: Theories for multiple resonances

abstract:
  Two microscopic theories for multiple resonances in nuclei are compared,
n-particle-hole RPA and quantized Time-Dependent Hartree-Fock (TDHF). The
Lipkin-Meshkov-Glick model is used as test case. We find that quantized TDHF is
superior in many respects, except for very small systems.


title: Constituent Quark Model Calculation for a possible J^P=0^-,T=0 Dibaryon

abstract:
  There exists experimental evidence that a dibaryon resonance d' with quantum
numbers J^P=0^-,T=0 and mass 2065 MeV could be the origin of the narrow peak in
the (\pi^+ ,\pi^- ) double charge exchange cross--sections on nuclei. We
investigate the six--quark system with these quantum--numbers within the
constituent quark model, with linear confinement, effective one--gluon exchange
at short range and chiral interactions between quarks (\pi and \sigma
exchange). We classify all possible six quark states with J^P=0^-,T=0, and with
N=1 and N=3 harmonic oscillator excitations, using different reduction chains.
The six--quark Hamiltonian is diagonalized in the basis including the unique
N=1 state and the 10 most important states from the N=3 shell. We find, that
with most of the possible sets of parameters, the mass of such a "dibaryon"
lies above the N(939)+N^\ast(1535) threshold. The only possibility to describe
the supposed d'(2065) in the present context is to reduce the confinement
strength to very small values, however at the expense of describing the
negative parity resonances N^\ast. We also analyze the J^P=0^-,T=2,N=1
six--quark state.


title: Strange Particle Production from Quark Matter Droplets

abstract:
  We recently introduced new methods to study ultrarelativistic nuclear
scattering by providing a link between the string model approach and a thermal
description. The string model is used to provide information about fluctuations
in energy density. Regions of high energy density are considered to be quark
matter droplets and treated macroscopically. At SPS energies, we find mainly
medium size droplets --- with energies up to few tens of GeV. A key issue is
the microcanonical treatment of individual quark matter droplets. Each droplet
hadronizes instantaneously according to the available n-body phase space. Due
to the huge number of possible hadron configurations, special Monte Carlo
techniques have been developed to calculate this disintegration. We present
results concerning the production of strange particles from such a
hadronization as compared to string decay.


title: Time-odd components in the mean field of rotating superdeformed nuclei

abstract:
  Rotation-induced time-odd components in the nuclear mean field are analyzed
using the Hartree-Fock cranking approach with effective interactions SIII,
SkM*, and SkP. Identical dynamical moments ${{\cal J}^{(2)}}$ are obtained for
pairs of superdeformed bands $^{151}$Tb(2)--$^{152}$Dy(1) and
$^{150}$Gd(2)--$^{151}$Tb(1). The corresponding relative alignments strongly
depend on which time-odd mean-field terms are taken into account in the
Hartree-Fock equations.


title: Quantum Monte Carlo Calculations of $A\leq6$ Nuclei

abstract:
  The energies of $^{3}H$, $^{3}He$, and $^{4}He$ ground states, the
${\frac{3}{2}}^{-}$ and ${\frac{1}{2}}^{-}$ scattering states of $^{5}He$, the
ground states of $^{6}He$, $^{6}Li$, and $^{6}Be$ and the $3^{+}$ and $0^{+}$
excited states of $^{6}Li$ have been accurately calculated with the Green's
function Monte Carlo method using realistic models of two- and three-nucleon
interactions. The splitting of the $A=3$ isospin $T=\frac{1}{2}$ and $A=6$
isospin $T=1$, $J^{\pi} = 0^{+}$ multiplets is also studied. The observed
energies and radii are generally well reproduced, however, some definite
differences between theory and experiment can be identified.


title: Glauber isovector spin responses for (p,n) reactions at 494 MeV

abstract:
  The separated isovector spin-longitudinal and spin-transverse responses from
a recent (p,n) quasifree experiment at 494 MeV are analyzed in a Glauber theory
framework up to two-step contributions. Nuclear correlations are treated in the
continuum random phase approximation, accounting for the spreading width of the
particle-hole states. A good description of the spin-longitudinal response is
achieved, hinting at some evidence of pionic effects in the quasielastic
region. The spin-transverse response is underestimated and we show that
multistep contributions, while sizable, are not sufficient to provide an
explanation of the discrepancy.


title: Kaon Condensation in Neutron Star Matter with Hyperons

abstract:
  Based on the Kaplan-Nelson Lagrangian, we investigate kaon condensation in
dense neutron star matter allowing for the explicit presence of hyperons. Using
various models we find that the condensate threshold is sensitive to the
behavior of the scalar density; the more rapidly it increases with baryon
density, the lower is the threshold for condensation. The presence of hyperons,
particularly the $\Sigma^-$, shifts the threshold for $K^-$ condensation to a
higher density. In the mean field approach, with hyperons, the condensate
amplitude grows sufficiently rapidly that the nucleon effective mass vanishes
at a finite density and a satisfactory treatment of the thermodynamics cannot
be achieved. Thus, calculations of kaon-baryon interactions beyond the mean
field level appear to be necessary.


title: Relativistic Quantum Transport Theory for Electrodynamics

abstract:
  We investigate the relationship between the covariant and the
three-dimensional (equal-time) formulations of quantum kinetic theory. We show
that the three-dimensional approach can be obtained as the energy average of
the covariant formulation. We illustrate this statement in scalar and spinor
QED. For scalar QED we derive Lorentz covariant transport and constraint
equations directly from the Klein-Gordon equation rather than through the
previously used Feshbach-Villars representation. We then consider pair
production in a spatially homogeneous but time-dependent electric field and
show that the pair density is derived much more easily via the energy averaging
method than in the equal-time representation. Proceeding to spinor QED, we
derive the covariant version of the equal-time equation derived by
Bialynicki-Birula et al. We show that it must be supplemented by another
self-adjoint equation to obtain a complete description of the covariant spinor
Wigner operator. After spinor decomposition and energy average we study the
classical limit of the resulting three-dimensional kinetic equations. There are
only two independent spinor components in this limit, the mass density and the
spin density, and we derive also their covariant equations of motion. We then
show that the equal-time kinetic equation provides a complete description only
for constant external electromagnetic fields, but is in general incomplete. It
must be supplemented by additional constraints which we derive explicitly from
the covariant formulation.


title: NUCLEAR THEORY WHITE PAPER 1995

abstract:
  We review the accomplishments of nuclear theory during the past five years
and identify the future challenges and research opportunities. [Final,
substantially revised version of the nuclear theory white paper]


title: NUCLEAR ASTROPHYSICS WITH SECONDARY (RADIOACTIVE) BEAMS

abstract:
  Some problems in nuclear astrophysics are discussed with emphasize on the
ones central to the field which were not solved over the last two decades,
including Helium Burning in Massive stars (the 12C(a,g)16O reaction) and the 8B
Solar Neutrino Flux Problem (the 7Be(p,g)8B reaction). We demonstrate that a
great deal of progress was achieved by measuring the time reverse process(es):
the beta-delayed alpha-particle emission of 16N and the Coulomb dissociation of
8B, using radioactive beams (of 16N and 8B). In this way an amplification of
the sought for cross section was achieved, allowing a measurement of the small
cross section(s) of relevance for stellar (solar) process(es).


title: Tables of SU(3) Isoscalar Factors

abstract:
  The Clebsch-Gordan coefficients of $SU(3)$ are useful in calculations
involving baryons and mesons, as well as in calculations involving arbitrary
numbers of quarks. For the latter case, one needs the coupling constants
between states of nonintegral hypercharges. The existing published tables are
insufficient for many such applications, and therefore we have compiled this
collection. This report supplies the isoscalar factors required to reconstruct
the Clebsch-Gordan coefficients for a large set of products of representations.


title: Correlations and Fluctuations in High-Energy Nuclear Collisions

abstract:
  Nucleon correlations in the target and projectile nuclei are shown to reduce
significantly the fluctuations in multiple nucleon-nucleon collisions, total
multiplicity and transverse energy in relativistic heavy-ion collisions, in
particular for heavy projectile and target. The interplay between cross-section
fluctuations, from color transparency and opacity, and nuclear correlations is
calculated and found to be able to account for large fluctuations in transverse
energy spectra. Numerical implementation of correlations and cross-section
fluctuations in Monte-Carlo codes is discussed.


title:
Muonic molecules of charge Z >= 3: Coulombic properties and nuclear
  transitions.

abstract:
  In this report we will discuss properties of and models for nuclear
transitions in muonic molecules formed via collisions of muonic atoms of
hydrogen isotopes with light nuclei like $L\!i$ and $B\!e$. Their importance
for nuclear astrophysics and nuclear physics at super low energies is
emphasized.


title:
Covariant four-dimensional scattering equations for the $NN-\pi NN$
  system

abstract:
  We derive a set of coupled four-dimensional integral equations for the
$NN-\pi NN$ system using our modified version of the Taylor method of
classification-of-diagrams. These equations are covariant, obey two and
three-body unitarity and contain subtraction terms which eliminate the
double-counting present in some previous four-dimensional $NN-\pi NN$
equations. The equations are then recast into a from convenient for computation
by grouping the subtraction terms together and obtaining a set of two-fragment
scattering equations for the amplitudes of interest.


title:
Relativistic treatment of the charged-current reaction ${}^{12}{\rm
  C}(\nu_{\mu},\mu^{-})$ near threshold

abstract:
  We compute the cross section for the charged-current reaction ${}^{12}{\rm
C}(\nu_{\mu},\mu^{-})$ near threshold using a relativistic mean-field
formalism. A reduced value of the nucleon mass in the medium --- coupled to the
finite muon mass --- leads to a 30\% reduction in the cross section relative to
a free Fermi-gas estimate. Isovector RPA correlations, which are strongly
repulsive at these momentum transfers, reduce the cross section by an
additional 15-30\%. Hence, relativistic nuclear-structure effects can account
for the more than a factor-of-two reduction in the cross section recently
reported by the LSND collaboration.


title:
Scissors Modes and Spin Excitations in Light Nuclei including $\Delta
  N$=2 excitations: Behaviour of $^8Be$ and $^{10}Be$

abstract:
  Shell model calculations are performed for magnetic dipole excitations in
$^8{Be}$ and $^{10}{Be}$ in which all valence configurations plus
$2\hbar\omega$ excitations are allowed (large space). We study both the orbital
and spin excitations. The results are compared with the `valence space only'
calculations (small space). The cumulative energy weighted sums are calculated
and compared for the $J=0^+$ $T$=0 to $J=1^+$ $T$=1 excitations in $^8{Be}$ and
for $J=0^+$ $T$=1 to both $J=1^+$ $T$=1 and $J$=$1^+$ $T$=2 excitations in
$^{10}{Be}$. We find for the $J=0^+$ $T$=1 to $J=1^+$ $T$=1 isovector
{\underline {spin}} transitions in $^{10}{Be}$ that the summed strength in the
{\underline {large}} space is less than in the {\underline {small}} space. We
find that the high energy energy-weighted isovector orbital strength is smaller
than the low energy strength for transitions in which the isospin is changed,
but for $J=0^+$ $T$=1 to $J=1^+$ $T$=1 in $^{10}{Be}$ the high energy strength
is larger. We find that the low lying orbital strength in $^{10}{Be}$ is
anomalously small, when an attempt is made to correlate it with the $B(E2)$
strength to the lowest $2^+$ states. On the other hand a sum rule of Zheng and
Zamick which concerns the total $B(E2)$ strength is reasonably satisfied in
both $^8{Be}$ and $^{10}{Be}$. The Wigner supermultiplet scheme is a useful
guide in analyzing shell model results. In $^{10}Be$ and with a $Q \cdot Q$
interaction the T=1 and T=2 scissors modes are degenerate, with the latter
carrying 5/3 of the T=1 strength.


title: 1/N expansion formalism for high-spin states

abstract:
  The 1/$N$ expansion solutions for the interacting boson model are extended to
higher orders using computer algebra. The analytic results are compared with
those obtained from an exact diagonalization of the Hamiltonian and are shown
to be very accurate. The extended formulas for level energies and E2
transitions will be useful in the analysis of high-spin states in both normal
and superdeformed nuclei.


title:
QUARK MODEL DESCRIPTION OF THE N-N SYSTEM: MOMENTUM DISTRIBUTIONS,
  STRUCTURE FUNCTIONS AND THE EMC EFFECT

abstract:
  We employ a relativistic quark bag picture, the chromo-dielectric soliton
model, to discuss the quarks' symmetry structure and momentum distribution in
the $N$-$N$ system. Six-quark clusters are constructed in a constrained
mean-field calculation. The corresponding Hamiltonian contains not only an
effective interaction between the quarks and a scalar field, which is assumed
to parameterize all non-perturbative effects due to the non-linearity of QCD,
but also quark-quark interactions mediated through one-gluon-exchange. We also
evaluate the quark light-cone distribution functions, characterizing inclusive
deep-inelastic lepton scattering, for the nucleon as well as for the six-quark
structures. We find a competition between a softening of the quarks' momenta
through the increase of the confinement volume, and a hardening via the
admixture of higher symmetry configurations due to the color-electrostatic
one-gluon-exchange. These findings suggest an unexpected absence of
many-nucleon, multi-quark effects, even though six-quark structures should
represent a non-negligible part of the nuclear ground state.


title: Dilepton Production in Elementary Processes on the Nucleon

abstract:
  We study elementary processes for production of dileptons from nucleons,
either through NN bremsstrahlung or through photon-induced reactions. We
emphasize the dependence of the expected cross-sections on the electromagnetic
formfactor of the nucleon in the time-like regime and point out that the
mentioned reactions can provide important information on the validity of vector
meson dominance for the nucleon. We also study the off-shell dependence of the
formfactors.


title: Mean-field description of nuclear charge density distributions.

abstract:
  We propose a method to extract nuclear charge distributions from elastic
electron scattering data based upon a mean field approach. The nuclear charge
distributions are generated by solving the Schroedinger equation with a
mean-field potential expanded in terms of Hermite functions. The coefficients
of the potential are changed in order to obtain the best fit with the cross
section data. Applications to the $^{12}C$, $^{16}O$ $^{40}Ca$ and $^{208}Pb$
nuclei are presented.


title: Mean field effects in heavy-ion collisions at AGS energies

abstract:
  The question whether mean field effects exist in heavy-ion collisions at AGS
energies is studied in the framework of A Relativistic Transport (ART) model.
It is found that in central collisions of Au+Au at $P_{beam}/A=$11.6 GeV/c a
simple, Skyrme-type nuclear mean field satisfying the causality requirement
reduces the maximum baryon and energy densities reached in the cascade model by
about 30\% and 40\%, respectively. The mean field affects the inclusive, single
particle observables of various hadrons by at most 20\%. We show, however, that
the mean field causes a factor of 2.5 increase in the strength of the baryon
transverse collective flow.


title: GCM study of hexadecapole correlations in superdeformed $^{194}$Hg

abstract:
  The role of hexadecapole correlations in the lowest superdeformed band of
$^{194}$Hg is studied by self consistent mean field methods. The generator
coordinate method with particle number projection has been applied using
Hartree-Fock wave functions defined along three different hexadecapole paths.
In all cases, the ground state is not significantly affected by hexadecapole
correlations and the energies of the corresponding first excited hexadecapole
vibrational states lie high in energy. The effect of rotation is investigated
with the Skyrme-Hartree-Fock-Bogolyubov method and a zero range
density-dependent pairing interaction.


title: The Fubini-Furlan-Rossetti sum rule reexamined

abstract:
  We review the status of a Fubini-Furlan-Rossetti sum rule for the
photoproduction of pions from nucleons, indicating how well this sum rule is
satisfied using a recent analysis of pion photoproduction data. Our results are
discussed in light of a recent paper comparing the Gerasimov-Drell-Hearn and
spin-dependent polarizability sum rules.


title: HOT GLUON PROPAGATOR

abstract:
  A general expression of the hard thermal loop gluon propagator is given for a
variety of abelian gauge fixing conditions (Coulomb gauge, axial gauge,
covariant gauge, temporal gauge ...) The current --- current interaction
energy, in particular the Coulomb energy, is shown to be independent of the
gauge fixing condition (not only of the parameter).


title:
Photon-Photon Luminosities in Relativistic Heavy Ion Collisions at LHC
  Energies

abstract:
  Effective photon-photon luminosities are calculated for various realistic
hadron collider scenarios. The main characteristics of photon-photon processes
at relativistic heavy-ion colliders are established and compared to the
corresponding photon-photon luminosities at electron-positron and future Photon
Linear Colliders (PLC). Higher order corrections as well as inelastic processes
are discussed. It is concluded that feasible high luminosity Ca-Ca collisions
at the Large Hadron Collider (LHC) are an interesting option for photon-photon
physics up to about 100 GeV photon-photon CM energy.


title:
Precise solution of few-body problems with the stochastic variational
  method

abstract:
  A precise variational solution to $N$=2--6-body problems is reported. The
trial wave functions are chosen to be combinations of correlated Gaussians,
which facilitate a fully analytical calculation of the matrix elements. The
nonlinear parameters of the trial function are selected by a stochastic method.
Fermionic and bosonic few-body systems are investigated for interactions of
different type. A comparison of the results with those available in the
literature shows that the method is both accurate and efficient.


title:
Hadron-nucleon Total Cross Section Fluctuations from Hadron-nucleus
  Total Cross Sections

abstract:
  The extent to which information about fluctuations in hadron-nucleon total
cross sections in the frozen approximation can be extracted from very high
energy hadron-nucleus total cross section measurements for a range of heavy
nuclei is discussed. The corrections to the predictions of Glauber theory due
to these fluctuations are calculated for several models for the distribution
functions, and differences of the order of 50 mb are found for heavy nuclei.
The generating function for the moments of the hadron-nucleon cross section
distributions can be approximately determined from the derivatives of the
hadron-nucleus total cross sections with respect to the nuclear geometric cross
section. The argument of the generating function, however, it limited to the
maximum value of a dimensionless thickness function obtained at zero impact
parameter for the heaviest nuclear targets: about 1.8 for pions and 3.0 for
nucleons.


title:
Short-range correlations in (e,e$'$p) and (e,e$'$pp) reactions on
  complex nuclei

abstract:
  The influence of short-range correlations (SRC) on the triple-coincidence
(e,e$'$pp) reactions is studied. The non-relativistic model uses a mean-field
potential to account for the distortions that the escaping particles undergo.
Apart from the SRC, that are implemented through a Jastrow ansatz with a
realistic correlation function, we incorporate the contribution from pion
exchange and intermediate $\Delta _{33}$ currents. The (e,e$'$pp) cross
sections are predicted to exhibit a sizeable sensitivity to the SRC. The
contribution from the two-nucleon breakup channel to the semi-exclusive
$^{12}$C(e,e$'$p) cross section is calculated in the kinematics of a recent
NIKHEF-K experiment. In the semi-exclusive channel, a selective sensitivity in
terms of the missing energy and momentum to the SRC is found.


title: Two-body currents in inclusive electron scattering

abstract:
  The longitudinal and transverse structure functions are calculated for
inclusive electron scattering from ${}^{12}$C and ${}^{40}$Ca in the
quasielastic and dip region. The microscopic model presented here incorporates
two-body currents derived from one-pion exchange and intermediate $\Delta$
excitation. The reaction mechanism involves both one-nucleon and two-nucleon
knockout processes. It is demonstrated that, even for quasielastic kinematics,
two-body currents give a substantial contribution to the transverse structure
function. Furthermore, the observed excess of transverse strength in the dip
region between the quasielastic and delta peak can be partially ascribed to
direct two-nucleon knockout following photoabsorption on a two-body current.


title: Composite vertices that lead to soft form factors

abstract:
  The momentum-space cut-off parameter $\Lambda$ of hadronic vertex functions
is studied in this paper. We use a composite model where we can measure the
contributions of intermediate particle propagations to $\Lambda$. We show that
in many cases a composite vertex function has a much smaller cut-off than its
constituent vertices, particularly when light constituents such as pions are
present in the intermediate state. This suggests that composite
meson-baryon-baryon vertex functions are rather soft, i.e., they have \Lambda
considerably less than 1 GeV. We discuss the origin of this softening of form
factors as well as the implications of our findings on the modeling of nuclear
reactions.


title: Nonperturbative treatment of the N-body system with dynamical mesons

abstract:
  The variational approach, used by Feynman in the study of the polaron
problem, is generalized to treat a system of N non-relativistic particles
interacting with scalar and vector mesons. After integrating out the meson
fields in the path integral formulation we perform a variational calculation
for the effective N-body two-time action to obtain the energy and the mass of
the system. The interplay of self energies and exchange terms in attaining
binding and saturation is examined. We estimate the size of the particles in
the medium and give the mean number of mesons as a function of N.


title:
CHIRAL SYMMETRY CONSTRAINTS ON THE $K^+$ INTERACTION WITH THE NUCLEAR
  PION CLOUD

abstract:
  The real part of the $K^{+}$ selfenergy for the interaction of the $K^{+}$
with the pion nuclear cloud is evaluated in lowest order of chiral perturbation
theory and is found to be exactly zero in symmetric nuclear matter. This
removes uncertainties in that quantity found in former phenomenological
analyses and is supported by present experimental data on $K^{+}$ nucleus
scattering.


title:
Dynamical fluctuations in the one particle density - comparison of
  different approaches

abstract:
  Diffusion coefficients are obtained from linear response functions and from
the quantal fluctuation dissipation theorem. They are compared with the results
of both the theory of hydrodynamic fluctuations by Landau and Lifschitz as well
as the Boltzmann-Langevin theory. Sum rules related to conservation laws for
total particle number, momentum and energy are demonstrated to hold true for
fluctuations and diffusion coefficients in the quantum case.


title: Repulsive Short Range Three-Nucleon Interaction

abstract:
  The three nucleon interaction that arises from pion and the effective scalar
and vector meson exchange components of the nucleon-nucleon interaction is
constructed and shown to be repulsive. Using several wavefunction models we
show that this interaction reduces the calculated binding energy of the
trinucleons by about 200 keV. The contributions of intermediate $N$(1440)
resonances to this three nucleon interaction and of the $D$-state component in
the trinucleon model are estimated, and shown to be small.


title: Measuring hadron properties at finite temperature

abstract:
  We estimate the numbers and mass spectra of observed lepton and kaon pairs
produced from $\phi$ meson decays in the central rapidity region of an Au+Au
collision at lab energy 11.6 GeV/nucleon. The following effects are considered:
possible mass shifts, thermal broadening due to collisions with hadronic
resonances, and superheating of the resonance gas. Changes in the dilepton mass
spectrum may be seen, but changes in the dikaon spectrum are too small to be
detectable.


title: Heavy Resonance Production in Ultrarelativistic Nuclear Collisions

abstract:
  Are heavy quarks produced thermally or only by hard parton collisions? What
is the probability that a produced heavy quark or antiquark is observed in a
given resonance?


title:
Triangle Diagram with Off-Shell Coulomb T-Matrix for (In-)Elastic Atomic
  and Nuclear Three-Body Processes

abstract:
  The driving terms in three-body theories of elastic and inelastic scattering
of a charged particle off a bound state of two other charged particles contain
the fully off-shell two-body Coulomb T-matrix describing the intermediate-state
Coulomb scattering of the projectile with each of the charged target particles.
Up to now the latter is usually replaced by the Coulomb potential, either when
using the multiple-scattering approach or when solving three-body integral
equations. General properties of the exact and the approximate on-shell driving
terms are discussed, and the accuracy of this approximation is investigated
numerically, both for atomic and nuclear processes including bound-state
excitation, for energies below and above the corresponding three-body
dissociation threshold, over the whole range of scattering angles.


title:
Implications of the GALLEX Source Experiment for the Solar Neutrino
  Problem

abstract:
  We argue that, prior to the recent GALLEX $^{51}$Cr source experiment, the
excited state contributions to the $^{71}$Ga capture cross section for
$^{51}$Cr and $^7$Be neutrinos were poorly constrained, despite forward-angle
(p,n) measurements. We describe the origin of the uncertainties and estimate
their extent. We explore the implications of the source experiment for solar
neutrino capture in light of these uncertainties. A reanalysis of the $^7$Be
and $^8$B flux constraints and MSW solutions of the solar neutrino puzzle is
presented.


title:
Long-range behavior of the optical potential for the elastic scattering
  of charged composite particles

abstract:
  The asymptotic behavior of the optical potential, describing elastic
scattering of a charged particle $\alpha$ off a bound state of two charged, or
one charged and one neutral, particles at small momentum transfer
$\Delta_{\alpha}$ or equivalently at large intercluster distance
$\rho_{\alpha}$, is investigated within the framework of the exact three-body
theory. For the three-charged-particle Green function that occurs in the exact
expression for the optical potential, a recently derived expression, which is
appropriate for the asymptotic region under consideration, is used. We find
that for arbitrary values of the energy parameter the non-static part of the
optical potential behaves for $\Delta_{\alpha} \rightarrow 0$ as
$C_{1}\Delta_{\alpha} + o\,(\Delta_{\alpha})$. From this we derive for the
Fourier transform of its on-shell restriction for $\rho_{\alpha} \rightarrow
\infty$ the behavior $-a/2\rho_{\alpha}^4 + o\,(1/\rho_{\alpha}^4)$, i.e.,
dipole or quadrupole terms do not occur in the coordinate-space asymptotics.
This result corroborates the standard one, which is obtained by perturbative
methods. The general, energy-dependent expression for the dynamic
polarisability $C_{1}$ is derived; on the energy shell it reduces to the
conventional polarisability $a$ which is independent of the energy. We
emphasize that the present derivation is {\em non-perturbative}, i.e., it does
not make use of adiabatic or similar approximations, and is valid for energies
{\em below as well as above the three-body dissociation threshold}.


title: Off shell pi N amplitude and the p p->p p pi0 reaction

abstract:
  We have used a conventional model for the $pp \rightarrow pp \pi^{0}$
reaction consisting of the Born term plus the $s$-wave rescattering term. As a
novelty we have introduced the off shell dependence of the $\pi N$ $s$-wave
isoscalar amplitude. This amplitude is appreciably enhanced when one moves to
the off shell situations met in the problem and, as a consequence, the $pp
\rightarrow pp \pi^{0}$ cross section becomes considerably larger than with the
use of the $\pi N$ on shell amplitudes. Two different models for the off shell
extrapolation found in the literature have been used and the cross sections
obtained are large enough to account for the experimental data, although
uncertainties remain due to the incomplete knowledge of the off shell
extrapolation.


title: The eta-N S-wave scattering length in one resonance model

abstract:
  We show that the S-wave $\eta N$ scattering length can be extracted in a
model independent way within the scope of the multichannel model, but with the
restricting assumption that only one resonance is included per partial wave.
One has only to use the information on $\pi N$ elastic S-wave T-matrix at the
$\eta$ production threshold, and near threshold $\pi^{-} p \rightarrow \eta n$
total cross section. The results are independent of the particular
parametrization of the elastic T-matrix and of the number of channels. For the
described model the unitarity requires that the number of channels must be at
least three. These assumptions are more general then the assumptions of the
existing single resonance models up to now used for extracting the $\eta N$
S-wave scattering length. The agreement of our approach with former estimates
is anticipated and confirmed for all cases for which the input data agree with
the commonly accepted values.


title: Microcanonical Treatment of Hadronizing the Quark-Gluon Plasma

abstract:
  We recently introduced a completely new way to study ultrarelativistic
nuclear scattering by providing a link between the string model approach and a
statistical description. A key issue is the microcanonical treatment of
hadronizing individual quark matter droplets. In this paper we describe in
detail the hadronization of these droplets according to n-body phase space, by
using methods of statistical physics, i.e. constructing Markov chains of hadron
configurations.


title:
Toroidal quadrupole transitions associated to collective
  rotational-vibrational motions of the nucleus

abstract:
  In the frame of the algebraic Riemann Rotational Model one computes the
longitudinal, transverse and toroidal multipoles corresponding to the
excitations of low-lying levels in the ground state band of several even-even
nuclei by inelastic electron scattering (e,e'). Related to these transitions a
new quantity, which accounts for the deviations from the Siegert theorem, is
introduced. The intimate connection between the nuclear vorticity and the
dynamic toroidal quadrupole moment is underlined. Inelastic differential
cross-sections calculated at backscattering angles shows the dominancy of
toroidal form-factors over a broad range of momentum transfer.


title: The three-baryon $\Lambda NN$ potential

abstract:
  Using a three-baryon $\Lambda NN$ potential having a spin-independent
dispersive and a two-pion exchange components, realistic variational Monte
Carlo calculations have been performed for the $\Lambda$-seperation energy for
$^{5}_{\Lambda}$He. A relationship between strengths associated with both
pieces of $\Lambda NN$ force giving exact experimental $\Lambda$-seperation
energy has been obtained which then combined with our previous study on
$^{17}_{\,\,\Lambda}$O hypernucleus determines a unique and acceptable set of
strength parameters for $\Lambda NN$ potential. The $\Lambda NN$ force is found
important for the core polarization.


title: Quark Matter 95: Concluding Remarks

abstract: Highlights of Quark Matter 95 are discussed.


title:
Short-Range Correlations and the One-Body Density Matrix in Finite
  Nuclei

abstract:
  The effects of short-range correlations derived from a realistic
meson-exchange potential on the single-particle density matrix in finite nuclei
are investigated by analyzing the one-body density in terms of the natural
orbits. Basic features of these natural orbits and their spectral distributions
are discussed. For many observables it seems to be sufficient to approximate
the one-body density matrix in terms of those natural orbits, which exhibit the
largest occupation probabilities. For the investigation of the high-momentum
components in the single-particle density, however, it is important to take
into account natural orbits with small occupation probabilities, originating
from the single-particle Green function at large negative energies.


title: Cold Kaons from hot fireballs

abstract:
  The E814-collaboration has found a component of very low $m_t$ $K^+$ mesons
with a slope parameter of $T \sim 15 \, \rm MeV$. We will present a scenario
which explains the observed slope parameter and which allows us to predict the
expected slope parameter for kaons produced in heavier systems such as Au+Au.
We also will discuss the effect of the coulomb interaction on the structure of
the spectrum.


title:
Consistent Treatment of Propagator Modifications in Elastic
  Nucleon-Nucleus Scattering within the Spectator Expansion

abstract:
  The theory of the elastic scattering of a nucleon from a nucleus is presented
in the form of a Spectator Expansion of the optical potential. Particular
attention is paid to the treatment of the free projectile$\,-\,$nucleus
propagator when the coupling of the struck target nucleon to the residual
target must be taken into consideration. First order calculations within this
framework are shown for neutron total cross-sections and for proton scattering
for a number of target nuclides at a variety of energies. The calculated values
of these observables are in very good agreement with measurement.


title: Chiral Symmetry in Nuclei

abstract:
  The impact of chiral symmetry on nuclear physics is discussed in the context
of recent advances in the few-nucleon systems and of dimensional power
counting. The tractability of few-nucleon calculations, illustrated by very
recent solutions for $A = 2-6$, is shown to follow from power counting based on
chiral Lagrangians. The latter predicts the suppression of $N$-body forces, as
originally shown by Weinberg. Isospin violation in the nuclear force is
similarly analyzed using the results of van Kolck, and this is shown to be
consistent with results from the Nijmegen phase-shift analysis. Conventional
$\rho - \omega$ and $\pi - \eta$ mixing models with on-shell mixing strength
are not inconsistent with naive power counting. Meson-exchange currents
calculated in chiral perturbation theory are in good agreement with experiment.


title: Implications of Theoretical Ideas Regarding Cold Fusion

abstract:
  A lot of theoretical ideas have been floated to explain the so called cold
fusion phenomenon. I look at a large subset of these and study further physical
implications of the concepts involved. I suggest that these can be tested by
other independent physical means. Because of the significance of these the
experimentalists are urged to look for these signatures. The results in turn
will be important for a better understanding and hence control of the cold
fusion phenomenon.


title: Effects of Pairing in the Pseudo-SU(3) Model

abstract:
  An extended version of the pseudo-SU(3) model which includes both spin and
proton-neutron degrees of freedom is used to study the influence of the pairing
interaction on K-band mixing, B(E2) values and quadrupole moments. Using the
asymmetric rotor model as a backdrop, specific consequences of a many-particle
shell-model based description of these collective properties are demonstrated
and fundamental limits of the collective model's approach are investigated.
Finally, the pseudo-SU(3) model, including representation mixing induced by
pairing, is used to calculate the energies of 140Ce and the results are
compared to experimental data and other theories.


title: Three-body halos. III. Effects of finite core-spin

abstract:
  We investigate effects of finite core-spin in two-neutron halos in the
three-body model consisting of two neutrons and a core. The states in the
neutron-core subsystem can then have an additional splitting due to the
coupling of the neutron and core spins. The connection between the structure of
the total system and the states of the neutron-core subsystem depends strongly
on this spin splitting. However, the spatial structure is essentially
unchanged. The neutron momentum distribution in a nuclear dissociation reaction
will consist of a broad and a narrow distribution arising from the two spin
split neutron-core virtual states. The large distance behavior is investigated
and the conditions for the Efimov effect turn out to be more restrictive. The
magnetic moment is equal to the core-value independent of spin splitting and
energies of the neutron-core states. The excited states of opposite parity
depend strongly on the spin splitting. The parameters in our numerical examples
are chosen to be appropriate for $^{11}$Li and $^{19}$B.


title:
Polaron Variational Methods In The Particle Representation Of Field
  Theory : I. General Formalism

abstract:
  We apply nonperturbative variational techniques to a relativistic scalar
field theory in which heavy bosons (``nucleons'') interact with light scalar
mesons via a Yukawa coupling. Integrating out the meson field and neglecting
the nucleon vacuum polarization one obtains an effective action in terms of the
heavy particle coordinates which is nonlocal in the proper time. As in
Feynman's polaron approach we approximate this action by a retarded quadratic
action whose parameters are to be determined variationally on the pole of the
two-point function. Several ans\"atze for the retardation function are studied
and for the most general case we derive a system of coupled variational
equations. An approximate analytic solution displays the instability of the
system for coupling constants beyond a critical value.


title: Strangeness Enhancement in $p+A$ and $S+A$ Interactions at SPS Energies

abstract:
  The systematics of strangeness enhancement is calculated using the HIJING and
VENUS models and compared to recent data on $\,pp\,$, $\,pA\,$ and $\,AA\,$
collisions at CERN/SPS energies ($200A\,\, GeV\,$). The HIJING model is used to
perform a {\em linear} extrapolation from $pp$ to $AA$. VENUS is used to
estimate the effects of final state cascading and possible non-conventional
production mechanisms. This comparison shows that the large enhancement of
strangeness observed in $S+Au$ collisions, interpreted previously as possible
evidence for quark-gluon plasma formation, has its origins in non-equilibrium
dynamics of few nucleon systems. % Strangeness enhancement %is therefore traced
back to the change in the production dynamics %from $pp$ to minimum bias $pS$
and central $SS$ collisions. A factor of two enhancement of $\Lambda^{0}$ at
mid-rapidity is indicated by recent $pS$ data, where on the average {\em one}
projectile nucleon interacts with only {\em two} target nucleons. There appears
to be another factor of two enhancement in the light ion reaction $SS$ relative
to $pS$, when on the average only two projectile nucleons interact with two
target ones.


title:
Dileptons from decay of vector mesons hadronized from a quark-gluon
  plasma

abstract:
  We present a simple model for the dimuon production from the decay of vector
mesons which are hadronized from a baryon-free quark-gluon plasma. Continuous
decay of vector mesons in the medium is known to enhance the dimuon production
and in our model we can estimate the total yield of dimuons decayed from vector
mesons through the rate equations for the number of vector mesons of interest.
Muon pair production critically depends on the time duration of both the mixed
and hadronic phases. Results are discussed in view of possible measurements in
experiments.


title:
Polaron Variational Methods In The Particle Representation Of Field
  Theory : II. Numerical Results For The Propagator

abstract:
  For the scalar Wick-Cutkosky model in the particle representation we perform
a similar variational calculation for the 2-point function as was done by
Feynman for the polaron problem. We employ a quadratic nonlocal trial action
with a retardation function for which several ans\"atze are used. The
variational parameters are determined by minimizing the variational function
and in the most general case the nonlinear variational equations are solved
numerically. We obtain the residue at the pole, study analytically and
numerically the instability of the model at larger coupling constants and
calculate the width of the dressed particle.


title:
Factorization Contributions and the Breaking of the $\Delta I=1/2$ Rule
  in Weak $\Lambda N\rho$ and $\Sigma N\rho$ Couplings

abstract:
  We compute the modified factorization contributions to the
$\Lambda\rightarrow N\rho$ and $\Sigma\rightarrow N\rho$ couplings and
demonstrate that these contributions naturally include $\Delta I=3/2$ terms
which are comparable ($\simeq 0.4$ to $-0.8$ times) in magnitude to the
corresponding $\Delta I=1/2$ terms. As a consequence, we conclude that models
which treat vector meson exchange contributions to the weak conversion process
$\Lambda N\rightarrow NN$ assuming such weak couplings to satisfy the $\Delta
I=1/2$ rule are unlikely to be reliable.


title:
Comment on ``Relativistic cluster dynamics of nucleons and mesons. II.
  Formalism and examples''

abstract:
  In a recent paper [Phys.\ Rev.\ C{\bf 49}, 2142 (1994)], Haberzettl presented
cluster N-body equations for arbitrarily large systems of nucleons and mesons.
Application to the three-nucleon system is claimed to yield a new kind of
three-nucleon force. We demonstrate that these three-nucleon equations contain
double counting.


title:
SPA+RPA approach to canonical and grandcanonical treatments of nuclear
  level densities

abstract:
  Using an exactly solvable pairing model Hamiltonian in the static path
approximation together with small-amplitude quantal fluctuation corrections in
random phase approximation (SPA+RPA), we have analyzed the behaviour of
canonical (number projected) and grandcanonical treatments of nuclear level
densities as a function of temperature and number of particles. For small
particle numbers at a low temperature, we find that though the grandcanonical
partition function in SPA+RPA approach is quite close to its exact value, the
small errors in its estimation causes significant suppression of level density
obtained using number projected partition function. The results are also
compared with the smoothed out exact values of level density. Within this model
study, it appears that due to saddle point approximation to multiple
Laplace-back transform, the grandcanonical treatment of level density at low
temperature may be reliable only for relatively large number of particles.


title: Relativistic Two-Body Processes in Axial-Charge Transitions

abstract:
  We study the contribution of two-body meson-exchange processes to axial
charge transitions for nuclei in the lead, tin and oxygen regions. We conduct
calculations in the Dirac-Hartree (the Walecka model) and the relativistic
Hartree (where the full one-nucleon-loop effects are included) approximations.
We present results indicating that one- and two-body processes enhance the
matrix elements of the axial-charge operator by some (100+-20)% in all three
regions studied. This agrees well with the fit of eighteen first-forbidden
beta-decay transitions conducted by Warburton in the lead region. We also
discuss some sensitivities present in the calculation.


title:
Description of inclusive scattering of few_GeV electrons from finite A
  nuclei and nuclear matter

abstract:
  We study $eA$ scattering in a model where the total nuclear structure
function is a convolution of components $W_N$ for an isolated nucleon and
$W_{\NA}$ for a nucleus composed of point-nucleons. $W_N$ is represented by its
elastic and lowest-energy inelastic parts, while $W_{\NA}$ is computed from its
asymptotic limit, supplemented by final state interactions due to binary
collisions between the knocked-out and core nucleons. $(q/M)W_{\NA}$ per
nucleon appears to be practically independent of mass number $A$ and momentum
transfer $q$. Consequently, predicted inclusive cross sections per nucleon for
given kinematic conditions hardly depend on the target and the same can be
extracted from the data. Exceptions are low energy loss regions, where
relatively small cross sections are shown to be sensitive to details of the
single nucleon momentum distribution and to FSI, involving multiple collisions.
The agreement with the data is good.


title: Charge Symmetry Breaking in 500 MeV Nucleon-Trinucleon Scattering

abstract:
  Elastic nucleon scattering from the 3He and 3H mirror nuclei is examined as a
test of charge symmetry violation. The differential cross-sections are
calculated at 500 MeV using a microsopic, momentum-space optical potential
including the full coupling of two spin 1/2 particles and an exact treatment of
the Coulomb force. The charge-symmetry-breaking effects investigated arise from
a violation within the nuclear structure, from the p-nucleus Coulomb force, and
from the mass-differences of the charge symmetric states. Measurements likely
to reveal reliable information are noted.


title: Triton calculations with $\pi$ and $\rho$ exchange three-nucleon forces

abstract:
  The Faddeev equations are solved in momentum space for the trinucleon bound
state with the new Tucson-Melbourne $\pi$ and $\rho$ exchange three-nucleon
potentials. The three-nucleon potentials are combined with a variety of
realistic two-nucleon potentials. The dependence of the triton binding energy
on the $\pi NN$ cut-off parameter in the three-nucleon potentials is studied
and found to be reduced compared to the case with pure $\pi$ exchange. The
$\rho$ exchange parts of the three-nucleon potential yield an overall repulsive
effect. When the recommended parameters are employed, the calculated triton
binding energy turns out to be very close to its experimental value.
Expectation values of various components of the three-nucleon potential are
given to illustrate their significance for binding.


title: Strong and Electromagnetic Interactions

abstract:
  Elements of a new model of strong interactions are described. The model is
based on an extension of electrodynamics that is derived from a regular
Lagrangian density. Here the electric and magnetic fields of Maxwell equations
play a symmetric role. It is shown that results are in accordance with general
properties of nuclear and nucleon systems.


title: Order and Chaos in Roto--Vibrational States of Atomic Nuclei

abstract:
  Using a classical analytical criterion (that of curvature) and numerical
results (Poincar\`e sections and spectral statistics), a transition
order--chaos--order in the roto--vibrational model of atomic nuclei has been
shown. Numerical calculations were performed for some deformed nuclei.


title: CURRENTS AND THEIR COUPLINGS IN THE WEAK SECTOR OF THE STANDARD MODEL

abstract:
  Beta-decay and muon-capture experiments in nuclei are reviewed. The conserved
vector current hypothesis is confirmed through the observed constancy of the
vector coupling constant determined from the superallowed Fermi transitions and
from the measurement of the weak-magnetism term in mirror Gamow-Teller
transitions. The axial-vector and pseudoscalar coupling constants in the
nucleon are determined from neutron decay and muon capture on the proton
respectively. In finite nuclei, evidence for these coupling constants being
reduced relative to their free-nucleon values is discussed. Meson-exchange
currents are shown to be an important correction to the time-like part of the
axial current as evident in first-forbidden beta decays. Tests of the Standard
Model are discussed, as well as extensions beyond it involving right-hand
currents and scalar interactions.


title: Boson-fermion mapping of collective fermion-pair algebras

abstract:
  We construct finite Dyson boson-fermion mappings of general collective
algebras extended by single-fermion operators. A key element in the
construction is the implementation of a similarity transformation which
transforms boson-fermion images obtained directly from the supercoherent state
method. In addition to the general construction, we give detailed applications
to SO(2N), SU(l+1), SO(5), and SO(8) algebras.


title: Isospin-mixing corrections for fp-shell Fermi transitions

abstract:
  Isospin-mixing corrections for superallowed Fermi transitions in {\it
fp}-shell nuclei are computed within the framework of the shell model. The
study includes three nuclei that are part of the set of nine accurately
measured transitions as well as five cases that are expected to be measured in
the future at radioactive-beam facilities. We also include some new
calculations for $^{10}$C. With the isospin-mixing corrections applied to the
nine accurately measured $ft$ values, the conserved-vector-current hypothesis
and the unitarity condition of the Cabbibo-Kobayashi-Maskawa (CKM) matrix are
tested.


title:
Relativistic Hydrodynamics for Heavy--Ion Collisions -- I. General
  Aspects and Expansion into Vacuum

abstract:
  We present algorithms to solve relativistic hydrodynamics in 3+1--dimensional
situations without apparent symmetry to simplify the solution. In simulations
of heavy--ion collisions, these numerical schemes have to deal with the
physical vacuum and with equations of state with a first order phase transition
between hadron matter and a quark--gluon plasma. We investigate their
performance for the one--dimensional expansion of baryon-free nuclear matter
into the vacuum, which is an analytically solvable test problem that
incorporates both the aspect of the vacuum as well as that of a phase
transition in the equation of state. The dependence of the lifetime of the
mixed phase on the initial energy density is discussed.


title: Shell-model Monte Carlo studies of fp-shell nuclei

abstract:
  We study the gross properties of even-even and $N=Z$ nuclei with $A=48-64$
using shell-model Monte Carlo methods. Our calculations account for all $0
\hbar \omega$ configurations in the $fp$-shell and employ the modified
Kuo-Brown interaction KB3. We find good agreement with data for masses and
total $B(E2)$ strengths, the latter employing effective charges $e_p=1.35e$ and
$e_n=0.35e$. The calculated total Gamow-Teller strengths agree consistently
with the $B(GT_+)$-values deduced from $(n,p)$ data if the shell model results
are renormalized by $0.64$, as has already been established for $sd$-shell
nuclei. The present calculations therefore suggest that this renormalization
(i.e., $g_A=1$ in the nuclear medium) is universal.


title: Threshold scattering of the eta-meson off light nuclei

abstract:
  The scattering lengths of eta-meson collisions with light nuclei d,t,3He, and
4He are calculated on the basis of few-body equations in coherent
approximation. It is found that the eta-nucleus scattering length depends
strongly on the number of nucleons and the potential-range parameter. By taking
into account the off-shell behavior of the eta-N amplitude, the eta-4He
scattering length increases considerably.


title:
Relativistic Hydrodynamics for Heavy--Ion Collisions -- II. Compression
  of Nuclear Matter and the Phase Transition to the Quark--Gluon Plasma

abstract:
  We investigate the compression of nuclear matter in relativistic
hydrodynamics. Nuclear matter is described by a $\sigma-\omega$--type model for
the hadron matter phase and by the MIT bag model for the quark--gluon plasma,
with a first order phase transition between both phases. In the presence of
phase transitions, hydrodynamical solutions change qualitatively, for instance,
one-dimensional stationary compression is no longer accomplished by a single
shock but via a sequence of shock and compressional simple waves. We construct
the analytical solution to the ``slab-on-slab'' collision problem over a range
of incident velocities. The performance of numerical algorithms to solve
relativistic hydrodynamics is then investigated for this particular test case.
Consequences for the early compressional stage in heavy--ion collisions are
pointed out.