title: Extracting Nuclear Transparency from p-A Cross sections

abstract:
  We study nuclear structure effects on the transparency in high transverse
momentum $(p,2p)$ and $(e,e'p)$ reactions. We show that in the DWIA-eikonal
approximation, even when correlations are included, one can get a factorized
expression for the transparency. This depends only on the average nucleon
density $\rho(r)$ and a correlation function. We develop a technique to include
correlations in a Monte-Carlo Glauber type calculation. We compare calculations
of $T$ using the eikonal formalism and a continuous density, with a Monte Carlo
method based on discrete nucleons.


title: Relativistic Ring-Diagram Nuclear Matter Calculations

abstract:
  A relativistic extension of the particle-particle hole-hole ring-diagram
many-body formalism is developed by using the Dirac equation for
single-particle motion in the medium. Applying this new formalism, calculations
are performed for nuclear matter. The results show that the saturation density
is improved and the equation of state becomes softer as compared to
corresponding Dirac-Brueckner-Hartree-Fock calculations. Using the Bonn A
potential, nuclear matter is predicted to saturate at an energy per nucleon of
--15.30 MeV and a density equivalent to a Fermi momentum of 1.38 fm$^{-1}$, in
excellent agreement with empirical information. The compression modulus is 152
MeV at the saturation point.


title:
Exact Solutions of Model Hamiltonian Problems with Effective
  Interactions

abstract:
  We demonstrate with soluble models how to employ the effective Hamiltonian
approach of Lee and Suzuki to obtain all the exact eigenvalues of the full
Hamiltonian. We propose a new iteration scheme to obtain the effective
Hamiltonian and demonstrate its convergence properties.


title:
Momentum distribution of fragments in heavy ion reactions: Dependence on
  the stochastic collision process

abstract:
  Momentum distribution of fragments produced in 12C+12C reaction at 28.7
MeV/nucleon is analyzed with antisymmetrized version of molecular dynamics
(AMD). Calculations are made for several cases of stochastic collisions and the
projectile fragmentation peak in momentum distribution is reproduced by the
incorporation of many-body nature in stochastic collision process. Furthermore
the value of the cross section is found to be reflected in the low momentum
part of fragments such as alpha particles and 9Be.


title:
Correlation between the quenching of total GT+ strength and the increase
  of E2 strength

abstract:
  Relations between the total beta+ Gamow-Teller (GT+) strength and the E2
strength are further examined. It is found that in shell-model calculations for
N=Z nuclei, in which changes in deformation are induced by varying the
single-particle energies, the total GT+ or GT- strength decreases monotonically
with increasing values of the B(E2) from the ground state to the first excited
J=2+ state. Similar trends are also seen for the double GT transition amplitude
(with some exceptions) and for the spin part of the total M1 strength as a
function of B(E2).


title: Shadowing in Deuterium

abstract:
  We calculate nuclear shadowing in lepton-deuteron deep inelastic scattering,
which arises from the double scattering of the virtual photon from both
nucleons in the deuteron. The total correction to the deuteron structure
function is found to be less than about 1\% at small Bjorken-x, but dependent
on the model deuteron wavefunction. The resulting increase in the corrected
neutron structure function is between 1-2\% for x near 0.004, which leads to a
4-10\% decrease in the value of the Gottfried sum obtained recently by the New
Muon Collaboration.


title: Role of Vector Mesons in High-Q^2 Lepton-Nucleon Scattering

abstract:
  The possible role played by vector mesons in inclusive deep inelastic
lepton-nucleon scattering is investigated. In the context of the convolution
model, we calculate self-consistently the scaling contribution to the nucleon
structure function using the formalism of time-ordered perturbation theory in
the infinite momentum frame. Our results indicate potentially significant
effects only when the vector meson---nucleon form factor is very hard.
Agreement with the experimental antiquark distributions, however, requires
relatively soft form factors for the $\pi N$, $\rho N$ and $\omega N$ vertices.


title:
The Astrophysical S-Factor of the Reaction $^7$be(p,$\gamma$)$^8$B in
  the Direct Capture Model

abstract:
  The astrophysical $S$-factor for the reaction $^7$Be(p,$\gamma$)$^8$B up to
an energy of 2~MeV (c.m.) and the capture cross section of
$^7$Li(n,$\gamma$)$^8$Li up to 1~MeV (c.m.) are calculated using the Direct
Capture model (DC). Both calculations are in good agreement with experimental
data.


title: Nucleon-Nucleon Potentials in Comparison: Physics or Polemics?

abstract:
  Guided by history, we review the major developments concerning realistic
nucleon-nucleon (NN) potentials since the pioneering work by Kuo and Brown on
the effective nuclear interaction. Our main emphasis is on the physics
underlying various models for the NN interaction developed over the past
quarter-century. We comment briefly on how to test the quantitative nature of
nuclear potentials properly. A correct calculation (performed by independent
researchers) of the $\chi^2$/datum for the fit of the world NN data yields 5.1,
3.7, and 1.9 for the Nijmegen, Paris, and Bonn potential, respectively.
Finally, we also discuss in detail the relevance of the on- and off-shell
properties of NN potentials for microscopic nuclear structure calculations.


title: Comment on Shadow model for sub-barrier fusion applied to light systems

abstract:
  We demonstrate that the cross sections derived from the "shadow model" for
reactions between light nuclei disagree with low-energy laboratory data and
exhibit unphysical behavior at energies below those for which data exist. As a
consequence, the large thermonuclear reaction rates obtained by Scalia and
Figuera [Phys. Rev. C46, 2610 (1992)] are wrong.


title: Self-Similarity and Scaling Behavior in Nuclear Collision

abstract:
  A simple model is used to explore issues related to self-similarity,
intermittency and scaling behavior in nuclear collisions. Both scaled factorial
moments and power moments are considered in the investigation of these
features. The product mass yields are used to construct probability
distributions and generalized Renyi entropies. The scaling properties of the
resulting Renyi entropies are studied. Both exponential and power law behavior
are found. A discussion of dimensions associated with these scaling properties
is also given. An analysis of some experimental data is presented.


title:
Geometry, Scaling and Universality in the Mass Distributions in Heavy
  Ion Collisions

abstract:
  Various features of the mass yields in heavy ion collisions are studied. The
mass yields are discussed in terms of iterative one dimensional discrete maps.
These maps are shown to produce orbits for a monomer or for a nucleus which
generate the mass yields and the distribution of cluster sizes. Simple
Malthusian dynamics and non-linear Verhulst dynamics are used to illustrate the
approach. Nuclear cobwebbing, attractors of the dynamics, and Lyapanov
exponents are discussed for the mass distribution. The self-similar property of
the Malthusian orbit offers a new variable for the study of scale invariance
using power moments of the mass distribution. Correlation lengths, exponents
and dimensions associated with scaling relations are developed. Fourier
transforms of the mass distribution are used to obtain power spectra which are
investigated for a $1/f^{\beta}$ behavior.


title:
Medium corrections to the tensor interaction in nuclei: Energy
  difference of T=1 and T=0 J=0- states in 16O

abstract:
  It has been shown in the past that in a shell model calculation, restricted
to 1Hbar*Omega 1p-1h configurations, the energy splitting between the lowest
J=0-, T=0 and J=0-, T=1 states in 16O is mainly due to the tensor component of
the nucleon-nucleon interaction. In this work, we extend the calculation to
include 3Hbar*Omega 2p-2h and 3p-3h configurations. We use realistic G matrices
derived from various One-Boson-Exchange potentials taking into account the
effects of the Dirac-Brueckner-Hartree-Fock approach, i.e., a modification of
the Dirac spinors for the nucleons in the medium. It is found that the
splitting is rather sensitive to the long-range components of the isovector
tensor force. The splitting is reduced considerably by including 2p-2h
configurations, in particular.


title: Test of Time Reversal Invariance in Proton Deuteron System

abstract:
  Internal target experiments with high quality proton beams allow for a new
class of experiments providing null tests of time reversal symmetry in forward
scattering. This could yield more stringent limits on T-odd P-even observables.
A excellent candidate for such experiments is the proton deuteron system. This
system is analyzed in terms of effective T-violating P-conserving
nucleon-nucleon interactions and bounds on coupling strengths that might be
expected are given.


title: Spin and Flavour: Concluding Remarks

abstract:
  Summmary talk at the Workshop on Sin and Flavour in Hadronic and
Electromagnetic Interactions, Turin (Italy), september 1992, to appear in the
Proceedings,


title:
Relativistic and Nuclear Structure Effects in Parity-Violating
  Quasielastic Electron Scattering

abstract:
  The parity violating longitudinal asymmetry ${\cal A}$ is calculated for
quasielastic electron scattering. We use a variety of relativistic mean field
models for the response of nuclear matter and $^{12}$C at a momentum transfer
of q=550 MeV/c. Relativistic effects from a reduced nucleon mass, RPA
correlations and vacuum polarization can all change ${\cal A}$ by a relatively
large amount. These large nuclear structure corrections could make it
impossible to extract strange quark matrix elements or radiative corrections to
weak axial currents.


title: Can Plasma Scattering Mimic a Cosmological Red-Shift?

abstract:
  We investigate the extent to which the scattering of light from plasma
fluctuations can mimic a cosmological red-shift, as has been suggested by Wolf
et al. A plasma model for the plasma structure function results in a spectrum
of scattered light very different from that associated with a constant
red-shift, implying that the "Wolf effect" cannot be involved to perturb the
cosmological distance scale.


title: The Beta Decay of 44V

abstract:
  We have calculated the $\beta^+$ decay of the proton rich nuclei $^{44}$V in
a full fp-shell valence space. We obtain a theoretical half-life of 71~ms
compared with the experimental value t$_{1/2}$ = 90 $\pm$ 25 ms. Besides, we
make predictions for the Gamow-Teller strength functions corresponding to the
decays of the 2$^+$ ground state and 6$^+$ isomer state.


title:
NN Core Interactions and Differential Cross Sections from One Gluon
  Exchange

abstract:
  We derive nonstrange baryon-baryon scattering amplitudes in the
nonrelativistic quark model using the ``quark Born diagram" formalism. This
approach describes the scattering as a single interaction, here the
one-gluon-exchange (OGE) spin-spin term followed by constituent interchange,
with external nonrelativistic baryon wavefunctions attached to the scattering
diagrams to incorporate higher-twist wavefunction effects. The short-range
repulsive core in the NN interaction has previously been attributed to this
spin-spin interaction in the literature; we find that these perturbative
constituent-interchange diagrams do indeed predict repulsive interactions in
all I,S channels of the nucleon-nucleon system, and we compare our results for
the equivalent short-range potentials to the core potentials found by other
authors using nonperturbative methods. We also apply our perturbative
techniques to the N$\Delta$ and $\Delta\Delta$ systems: Some $\Delta\Delta$
channels are found to have attractive core potentials and may accommodate
``molecular" bound states near threshold. Finally we use our Born formalism to
calculate the NN differential cross section, which we compare with experimental
results for unpolarised proton-proton elastic scattering. We find that several
familiar features of the experimental differential cross section are reproduced
by our Born-order result.


title:
The $^3S_1-^3D_1$ effective-range parameters of some realistic
  nucleon-nucleon potentials

abstract:
  We consider the $P$- and $Q$-shape parameters in the eigenphase and `bar'
phase shift representations for the two Reid potentials and the more recent
Moscow potential. The values of these parameters were obtained from integrals
of the zero-energy wave function in a similar manner to that for the effective
range. Such expressions for the shape parameters yield more reliable numerical
values of the shape parameter than those obtained by least-mean-square or
polynomial fits. We show that the eigenphase representation is more meaningful
than the `bar' phase shift representation and that the variation in the values
of $P_\alpha$ in the models may be of significance.


title:
Model for the Quasifree Polarization-Transfer Measurements in the (p,n)
  reaction at 495 MeV

abstract:
  The recent (p,n) polarization transfer experiments at LAMPF are explained in
terms of a dropping rho-meson mass in the medium.


title: Determination of two-body potentials from n-body spectra

abstract:
  We show how the two-body potential may be uniquely determined from n-body
spectra where the hypercentral approximation is valid. We illustrate this by
considering an harmonic oscillator potential which has been altered by changing
the energy or normalisation constant of the ground state of the n-body system
and finding how this modifies the two-body potential. It is shown that with
increasing number of particles the spectrum must be known more precisely to
obtain the two-body potential to the same degree of accuracy.


title: Modeling Complex Nuclear Spectra - Regularity versus Chaos

abstract:
  A statistical analysis of the spectrum of two particle - two hole doorway
states in a finite nucleus is performed. On the unperturbed mean-field level
sizable attractive correlations are present in such a spectrum. Including
particle-hole rescattering effects via the residual interaction introduces
repulsive dynamical correlations which generate the fluctuation properties
characteristic of the Gaussian Orthogonal Ensemble. This signals that the
underlying dynamics becomes chaotic. This feature turns out to be independent
of the detailed form of the residual interaction and hence reflects the generic
nature of the fluctuations studied.


title: Pre-equilibrium dileptons look thermal

abstract:
  The dilepton mass distribution from pre-equilibrium matter in
ultrarelativistic nuclear collisions is indistinguishable from a thermally
produced distribution.


title: The Coulomb Sum and Proton-Proton Correlations in Few-Body Nuclei

abstract:
  In simple models of the nuclear charge operator, measurements of the Coulomb
sum and the charge form factor of a nucleus directly determine the
proton-proton correlations. We examine experimental results obtained for
few-body nuclei at Bates and Saclay using models of the charge operator that
include both one- and two-body terms. Previous analyses using one-body terms
only have failed to reproduce experimental results. However, we find that the
same operators which have been used to successfully describe the charge form
factors also produce substantial agreement with measurements of the Coulomb
sum.


title:
Effective Hamiltonians with Relativistic Corrections I: The
  Foldy--Wouthuysen transformation versus the direct Pauli reduction

abstract:
  Two different methods of obtaining ``effective $2\times 2$ Hamiltonians''
which include relativistic corrections to nonrelativistic calculations are
discussed, the standard Foldy--Wouthuysen transformation and what we call the
``direct Pauli reduction''. We wish to investigate under which circumstances
the two approaches yield the same result. Using a generic interaction with
harmonic time dependence we show that differences in the corresponding
effective S--matrices do arise beyond first--order perturbation theory. We
attribute them to the fact that the use of the direct reduction effective
Hamiltonian involves the additional approximation of neglecting contributions
from the negative--energy intermediate states, an approximation which is
unnecessary in the Foldy--Wouthuysen case as there the $4\times 4$ Hamiltonian
does not connect positive-- and negative--energy states. We conclude that at
least in the cases where the relativistic Hamiltonian is known, using the
direct Pauli reduction effective Hamiltonian introduces spurious relativistic
effects and therefore the Foldy--Wouthuysen reduction should be preferred.


title:
Effective Hamiltonians with Relativistic Corrections II: Application to
  Compton Scattering by a Proton

abstract:
  We discuss two different methods of obtaining ``effective $2 \times 2$
Hamiltonians'' of the electromagnetic interaction which include relativistic
corrections. One is the standard Foldy--Wouthuysen transformation which we
compare with the Hamiltonian obtained from a direct reduction of the matrix
element of the interaction Hamiltonian between positive--energy solutions of
the free Dirac equation. The two approaches are applied to Compton scattering
by a proton for which a low--energy theorem exists. It is found that the
Foldy--Wouthuysen Hamiltonian yields the same result as a covariant
calculation. This is not true for the direct reduction method which will in
general lead to incorrect results even after restoring the gauge invariance
property of the Hamiltonian. Furthermore, it is shown that an identification of
the Z--diagrams of the usual Dirac representation with the contact graphs of
the Foldy--Wouthuysen representation is incorrect beyond the order of the
low--energy theorem.


title:
Particle-particle correlations and the space-time structure of heavy ion
  collisions

abstract:
  The present status of the use of two-particle intensity interferometry as a
diagnostic tool to study the space-time dynamics of intermediate energy heavy
ion collisions is examined. Calculations for the two-proton and two-pion
correlation functions are presented and compared to experiment. The
calculations are based on the nuclear Boltzmann-Uehling-Uhlenbeck transport
theory.


title: M1 Resonances in Unstable Magic Nuclei

abstract:
  Within a microscopic approach which takes into account RPA configurations,
the single-particle continuum and more complex $1p1h\otimes phonon$
configurations isoscalar and isovector M1 excitations for the unstable nuclei
${56,78}$Ni and ${100,132}$Sn are calculated. For comparison, the
experimentally known M1 excitations in ${40}$Ca and $^{208}$Pb have also been
calculated. In the latter nuclei good agreement in the centroid energy, the
total transition strength and the resonance width is obtained. With the same
parameters we predict the magnetic excitations for the unstable nuclei. The
strength is sufficiently concentrated to be measurable in radioactive beam
experiments. New features are found for the very neutron rich nucleus ${78}$Ni
and the neutron deficient nucleus ${100}$Sn.


title:
Generalized $^3P_0$ and $^3S_1$ Annihilation Potentials for $\bar{p}p$
  Decay into Two Mesons based on a Simple Quark Model

abstract:
  Within the quark model a generalization is proposed of the commonly used
annihilation potential to describe antiproton-proton annihilation into two
mesons, the so-called $^3P_0$ and $^3S_1$ mechanisms. This generalized
potential treats the two mechanisms in a more symmetric way, has additional
angular dependence, and results in an expanded set of selection rules.


title: Atomic parity nonconservation and neutron radii in cesium isotopes

abstract:
  The interpretation of future precise experiments on atomic parity violation
in terms of parameters of the Standard Model could be hampered by uncertainties
in the atomic and nuclear structure. While the former can be overcome by
measurement in a series of isotopes, the nuclear structure requires knowledge
of the neutron density. We use the nuclear Hartree-Fock method, which includes
deformation effects, to calculate the proton and neutron densities in
{125}Cs-{139}Cs. We argue that the good agreement with the experimental charge
radii, binding energies, and ground state spins signifies that the
phenomenological nuclear force and the method of calculation that we use is
adequate. Based on this agreement, and on calculations involving different
effective interactions, we estimate the uncertainties in the differences of the
neutron radii delta<r^2>_{N,N'} and conclude that they cause uncertainties in
the ratio of weak charges, the quantities determined in the atomic parity
nonconservation experiments, of less than 10^{-3}. Such an uncertainty is
smaller than the anticipated experimental error.


title: Parton Equilibration in Relativistic Heavy Ion Collisions

abstract:
  We investigate the processes leading to phase-space equilibration of parton
distributions in nuclear interactions at collider energies. We derive a set of
rate equations describing the chemical equilibration of gluons and quarks
including medium effects on the relevant QCD transport coefficients, and
discuss their consequences for parton equilibration in heavy ion collisions.


title: Off-shell Behavior of the $\pi\!-\!\eta$ Mixing Amplitude

abstract:
  We extend a recent calculation of the momentum dependence of the
$\rho-\omega$ mixing amplitude to the pseudoscalar sector. The $\pi\!-\!\eta$
mixing amplitude is calculated in a hadronic model where the mixing is driven
by the neutron-proton mass difference. Closed-form analytic expressions are
presented in terms of a few nucleon-meson parameters. The observed momentum
dependence of the mixing amplitude is strong enough as to question earlier
calculations of charge-symmetry-breaking observables based on the on-shell
assumption. The momentum dependence of the $\pi\!-\!\eta$ amplitude is,
however, practically identical to the one recently predicted for $\rho-\omega$
mixing. Hence, in this model, the ratio of pseudoscalar to vector mixing
amplitudes is, to a good approximation, a constant solely determined from
nucleon-meson coupling constants. Furthermore, by selecting these parameters in
accordance with charge-symmetry-conserving data and SU(3)-flavor symmetry, we
reproduce the momentum dependence of the $\pi\!-\!\eta$ mixing amplitude
predicted from chiral perturbation theory. Alternatively, one can use
chiral-perturbation-theory results to set stringent limits on the value of the
$NN\eta$ coupling constant.


title: The Onset of Color Transparency in $(e,e'p)$ Reactions on Nuclei

abstract:
  Quantum filtering of the ejectile wave packet from hard $ep$ scattering on
bound nucleons puts stringent constraints on the onset of color transparency in
$(e,e'p)$ reactions in nuclei at moderate energies. Based on
multiple-scattering theory, we derive a novel formula for nuclear transparency
and discuss its energy dependence in terms of a color transparency sum rule.


title: The neutron halo of $^6$He in a microscopic model

abstract:
  The two--neutron separation energy of $^6$He has been reproduced for the
first time in a realistic parameter--free microscopic multicluster model
comprising the $\alpha +n+n$ and $t+t$ clusterizations, with $\alpha$ cluster
breathing excitations included. The contribution of the $t+t$ channel is
substantial. A very thick (0.85 fm) neutron halo has been found in full
agreement with the results of the latest phenomenological analysis.


title:
Relation between the phenomenological interactions of the algebraic
  cluster model and the effective two--nucleon forces

abstract:
  We determine the phenomenological cluster--cluster interactions of the
algebraic model corresponding to the most often used effective two--nucleon
forces for the $^{16}$O + $\alpha$ system.


title: The response of non-relativistic confined systems

abstract:
  We study the non-relativistic response of a 'diquark' bound by confining
forces, for which perturbation theory in the interaction fails. As
non-perturbative alternatives we consider the Gersch-Rodriguez-Smith theory and
a summation method. We show that, contrary to the case of singular repulsive
forces, the GRS theory can generally be applied to confined systems. When
expressed in the GRS-West kinematic variable y, the response has a standard
asymptotic limit and calculable dominant corrections of orders 1/q,1/q. That
theory therefore clearly demonstrates how constituents, confined before and
after the absorption of the transferred momentum and energy, behave as
asymptotically free particles. We compare the GRS results with those for a
summation method for harmonic and square well confinement and also discuss the
convergence of the GRS series for the response in powers of 1/q.


title:
Ghost Poles in the Nucleon Propagator: Vertex Corrections and Form
  Factors

abstract:
  Vertex corrections are taken into account in the Schwinger-Dyson equation for
the nucleon propagator in a relativistic field theory of fermions and mesons.
The usual Hartree-Fock approximation for the nucleon propagator is known to
produce the appearance of complex (ghost) poles which violate basic theorems of
quantum field theory. In a theory with vector mesons there are vertex
corrections that produce a strongly damped vertex function in the ultraviolet.
One set of such corrections is known as the Sudakov form factor in quantum
electrodynamics. When the Sudakov form factor generated by massive neutral
vector mesons is included in the Hartree-Fock approximation to the
Schwinger-Dyson equation for the nucleon propagator, the ghost poles disappear
and consistency with basic requirements of quantum field theory is recovered.


title:
Orbital M1 versus E2 strength in deformed nuclei: A new energy weighted
  sum rule

abstract:
  Within the unified model of Bohr and Mottelson we derive the following linear
energy weighted sum rule for low energy orbital 1$^+$ excitations in even-even
deformed nuclei $$S_{\rm LE}^{\rm lew} (M_1^{\rm orb}) \cong (6/5) \epsilon
(B(E2; 0^+_1 \rightarrow 2_1^+ K=0)/Z e^2<r^2>^2) \mu^2_N$$ with B(E2) the E2
strength for the transition from the ground state to the first excited state in
the ground state rotational band, $<r^2>$ the charge r.m.s. radius squared and
$\epsilon$ the binding energy per nucleon in the nuclear ground state. It is
shown that this energy weighted sum rule is in good agreement with available
experimental data. The sum rule is derived using a simple ansatz for the
intrinsic ground state wave function that predicts also high energy 1$^+$
strength at 2$\hbar \omega$ carrying 50\% of the total $m_1$ moment of the
orbital M1 operator.


title: Left-Right Asymmetry in $\bar{p}p \rightarrow \pi^- \pi^+$

abstract:
  Results for d$\sigma$/d$\Omega$ and $A_N$ in the reaction $\bar{p}p
\rightarrow \pi^- \pi^+$ are predicted by a simple quark model. They are
compared to recent experimental data from LEAR, as well as to previous
predictions from nucleon-exchange models. At low energy the quark model does
better than the nucleon-exchange models, but the overall comparison to
experiment remains poor. In particular, the double-dip structure of the
experimental $A_N$ data is only partly represented. This shortcoming of the
simple quark model is traced back to a too small J=2 amplitude. This has
interesting implications for the range of this specific annihilation process.


title:
Angular Momentum Analysis of Spin 1/2 x 1/2 Scattering including
  Singlet-Triplet Mixing

abstract:
  The angular momentum (partial wave) reduction of the Lippmann--Schwinger
equation describing the interaction of two spin 1/2 particles is extended to
the case in which the spin singlet and triplet states are coupled. A straight
forward method for obtaining the angular momentum decomposition of the general
potential is indicated. The derived formalism is needed to describe the
interaction between two nonidentical spin--1/2 particles or between two
nucleons when isospin symmetry is violated. The resulting modification of the
Stapp phase--shift analysis is given.


title:
Critical test of multi-{\it j} supersymmetries from magnetic moment
  measurements

abstract:
  Magnetic moment measurements in odd nuclei directly probe the distribution of
fermion states and hence provide one of the most critical tests for multi-$j$
supersymmetries in collective nuclei. Due to complexity of calculations and
lack of data, such tests have not been performed in the past. Using the
Mathematica software, we derive analytic expressions for magnetic moments in
the $SO^{(BF)}(6) \times SU^{(F)}(2)$ limit of the $U(6/12)$ supersymmetry and
compare the results with recent measurements in $^{195}$Pt.


title: Probing Hadronic Structure with The Decay $\Delta\rightarrow Nl^+l^-$

abstract:
  We compute the branching ratio for $\Delta\rightarrow Ne^+e^-$ and
$\Delta\rightarrow N\mu^+\mu^-$ in chiral perturbation theory and find that
both decays should be observable at CEBAF. With sufficiently low thresholds on
the $e^+e^-$ invariant mass a branching ratio of $\sim 10^{-5}$ may be observed
for $\Delta\rightarrow Ne^+e^-$. For the $\Delta\rightarrow N\mu^+\mu^-$ decay
mode we predict a branching ratio of $3\times 10^{-7}$. The dependence of the
M1 and E2 amplitudes on the momentum transfer will provide a useful test of
chiral perturbation theory which predicts $\sim 20\%$ variation over the
allowed kinematic range.


title:
Nuclear effects in Deep Inelastic Scattering of polarized electrons off
  polarized 3He and the neutron spin structure functions

abstract:
  It is shown that the nuclear effects playing a relevant role in Deep
Inelastic Scattering of polarized electrons by polarized $^3$He are mainly
those arising from the effective proton and neutron polarizations generated by
the $S'$ and $D$ waves in $^3$He. A simple and reliable equation relating the
neutron, $g_1^n$, and $^3$He, $g_1^3$, spin structure functions is proposed. It
is shown that the measurement of the first moment of the $^3$He structure
function can provide a significant check of the Bjorken Sum Rule.


title:
Quantum theory of large amplitude collective motion and the
  Born-Oppenheimer method

abstract:
  We study the quantum foundations of a theory of large amplitude collective
motion for a Hamiltonian expressed in terms of canonical variables. In previous
work the separation into slow and fast (collective and non-collective)
variables was carried out without the explicit intervention of the Born
Oppenheimer approach. The addition of the Born Oppenheimer assumption not only
provides support for the results found previously in leading approximation, but
also facilitates an extension of the theory to include an approximate
description of the fast variables and their interaction with the slow ones.
Among other corrections, one encounters the Berry vector and scalar potential.
The formalism is illustrated with the aid of some simple examples, where the
potentials in question are actually evaluated and where the accuracy of the
Born Oppenheimer approximation is tested. Variational formulations of both
Hamiltonian and Lagrangian type are described for the equations of motion for
the slow variables.


title: Dirac Hartree-Fock for Finite Nuclei Employing realistic Forces

abstract:
  We discuss two different approximation schemes for the self-consistent
solution of the {\it relativistic} Brueckner-Hartree-Fock equation for finite
nuclei. In the first scheme, the Dirac effects are deduced from corresponding
nuclear matter calculations, whereas in the second approach the local-density
approximation is used to account for the effects of correlations. The results
obtained by the two methods are very similar. Employing a realistic
one-boson-exchange potential (Bonn~A), the predictions for energies and radii
of $^{16}$O and $^{40}$Ca come out in substantially better agreement with
experiment as compared to non-relativistic approaches. As a by-product of our
study, it turns out that the Fock exchange-terms, ignored in a previous
investigation, are not negligible.


title:
On the Spectacular Large Asymmetry in $\pbarppipi$ and $\pbarpKK$
  Reactions}

abstract:
  An illustrative analysis is presented to show the origin of the
energy-independent maximal asymmetry observed for wide ranges of angles in the
reactions $\pbarppipi$ and $\pbarpKK$. % The general nature of our simple
relation between helicity -flip and -nonflip partial wave amplitudes enforces
the notion that % these features of the asymmetry for these two annihilation
reactions are likely to persist within the hadronic regime. % At higher
energies these features of the asymmetry will probably be modified
significantly, signaling the onset of perturbative QCD. % Our study supports
the arguments that the final $\KbarK$ state originates from a more central
reaction than the $\pipi$ final state.


title:
Exclusive Hadronic Reactions at High $Q^2$ ($90\degree$) and
  Polarization Phenomena, An Experimental Proposal}

abstract:
  Arguments are presented for the expected behaviour of $\piNpiN$ scattering
and the $\pbarppipi$ reaction at high energy and large scattering angles. % The
annihilation reaction has close to maximal asymmetry ($\approx$ 1) for $p_{lab}
\siml $ 2.2 GeV/c. % As will be presented for fixed (90$\degree$) angle this
large asymmetry will not become zero but will start to oscillate with energy at
higher energies and large $Q^2$ when perturbative QCD becomes applicable. This
is due to the energy dependence of a QCD phase difference between the
independent quark-quark scattering (Landshoff) and short-distance processes at
high but not asymptotic energies. % A consequence of the existence the
Landshoff process is that even if helicity is conserved at the quark level
($m_{q}$ = 0 MeV), helicity does not have to be conserved on the hadronic
level. % We will discuss the implications for spin observables in $pp$ elastic
scattering and argue that


title: The Quasi-Elastic Nuclear Response

abstract:
  We explore the nuclear responses at intermediate energies, particularly in
the spin longitudinal and spin transverse isovector channels, within the
continuum random phase approximation framework. We also employ an extension of
the standard random phase approximation to account for the spreading width of
the single particle states through the inclusion of a complex and
energy-dependent nucleon self-energy. The nuclear responses are then used as
the basic ingredient to calculate hadronic reactions in the Glauber theory
framework. Here both one and two-step contributions to the multiple scattering
series in the quasi-elastic peak region are taken into account. We find
evidence for shell effects in the one-step response and a strong dependence on
the momentum regime of the two-step contribution.


title: Comment on Neutron-Proton Spin-Correlation Parameter A_{ZZ} at 68 Mev

abstract:
  We present two arguments indicating that the large value for the $\epsilon_1$
mixing parameter at 50 MeV, which the Basel group extracted from their recent
$A_{zz}$ measurement, may be incorrect. First, there are nucleon-nucleon (NN)
potentials which predict the $\epsilon_1$ at 50 MeV substantially below the
Basel value and reproduce the Basel $A_{zz}$ data accurately. Second, the large
value for $\epsilon_1$ at 50 MeV proposed by the Basel group can only be
explained by a model for the NN interaction which is very unrealistic (no
$\rho$-meson and essentially a point-like $\pi NN$ vertex) and overpredicts the
$\epsilon_1$ in the energy range where it is well determined (150--500 MeV) by
a factor of two.


title: Correlations in Nuclei: Self-Consistent Treatment and the BAGEL Approach

abstract:
  An approach is presented which allows a self-consistent description of the
fragmentation of single-particle strength for nucleons in finite nuclei
employing the Greens function formalism. The self-energy to be considered in
the Dyson equation for the single-particle Greens function contains all terms
of first (Hartree-Fock) and second order in the residual interaction. It is
demonstrated that the fragmentation of the single-particle strength originating
from the terms of second order can efficiently be described in terms of the
so-called BAGEL approximation. Employing this approximation the self-energy can
be evaluated in a self-consistent way, i.e. the correlations contained in the
Greens function are taken into account for the evaluation of the self-energy.
As an example this scheme is applied to the nucleus $^{16}O$, using a realistic
nucleon nucleon interaction. The effects of the correlations on the occupation
probabilities and the binding energy are evaluated.


title: Light front dynamics and the binding correction

abstract:
  It is shown that the nuclear binding correction in deep inelastic lepton
scattering is essentially the same in light front and instant form
representations. Some contradicting papers are discussed.


title: Gauge Invariance and the Electromagnetic Current of Composite Pions

abstract:
  The Global Color-symmetry Model of QCD is extended to deal with a background
electromagnetic field and the associated conserved current is identified for
composite $\bar{q}q$ pion modes of the model. Although the analysis is limited
to tree level in the bilocal fields that bosonize the model, the identified
photon-pion vertex produces the charge form factor associated with ladder
Bethe-Salpeter pion amplitudes. A Ward-Takahashi identity for this vertex is
derived in terms of the effective inverse propagator for the equivalent local
pion field and the intrinsic ladder Bethe-Salpeter amplitudes. This identity is
then used to illustrate gauge invariance by showing that identical vertex
information is produced from the gauge change of the free action once proper
account is taken of the gauge transformation properties of the bilocal pion
fields. Comments are made on the location of the vector dominance mechanism in
this treatment.


title: Boson-fermion mappings for odd systems from supercoherent states

abstract:
  We extend the formalism whereby boson mappings can be derived from
generalized coherent states to boson-fermion mappings for systems with an odd
number of fermions. This is accomplished by constructing supercoherent states
in terms of both complex and Grassmann variables. In addition to a known
mapping for the full so(2$N$+1) algebra, we also uncover some other formal
mappings, together with mappings relevant to collective subspaces.


title: Nambu-Jona-Lasinio Models Beyond the Mean Field Approximation

abstract:
  Inspired by the model of Nambu and Jona-Lasinio, various Lagrangians are
considered for a system of interacting quarks. Employing standard techniques of
many-body theory, the scalar part of the quark self-energy is calculated
including terms up to second-order in the interaction. Results obtained for the
single-particle Green's function are compared with those which only account for
the mean-field or Hartree-Fock term in the self-energy. Depending on the
explicit form of the Lagrangian, the second-order contributions range between 4
and 90 percent of the leading Hartree-Fock term. This leads to a considerable
momentum dependence of the self-energy and the effective mass of the quarks.


title:
The Pion in Electromagnetic and Weak Neutral Current Nuclear Response
  Functions

abstract:
  The impact of pionic correlations and meson--exchange currents in determining
the (vector) response functions for electroweak quasielastic lepton scattering
from nuclei is discussed. The approach taken builds on previous work where the
Fermi gas model is used to maintain consistency in treating forces and currents
(gauge invariance) and to provide a Lorentz covariant framework. Results
obtained in first-order perturbation theory are compared with infinite-order
summation schemes (HF and RPA) and found to provide quite successful
approximations for the quasielastic response functions. The role of pionic
correlations in hardening the responses R_L and R_T is investigated in some
detail, including studies of the relative importance of central and tensor
pieces of the force and of exchange and self-energy diagrams; in addition,
their role in significantly modifying the longitudinal parity-violating
response R_{AV}^L is explored. The MEC are shown to provide a small, but
non-negligible, contribution in determining the vector responses.


title:
Collective Modes in a Slab of Interacting Nuclear Matter: The effects of
  finite range interactions

abstract:
  We consider a slab of nuclear matter and investigate the collective
excitations, which develop in the response function of the system. We introduce
a finite-range realistic interaction among the nucleons, which reproduces the
full G-matrix by a linear combination of gaussian potentials in the various
spin-isospin channels. We then analyze the collective modes of the slab in the
S=T=1 channel: for moderate momenta hard and soft zero-sound modes are found,
which exhaust most of the excitation strength. At variance with the results
obtained with a zero range force, new "massive" excitations are found for the
vector-isovector channel .


title: Role of heavy-meson exchange in pion production near threshold

abstract:
  Recent calculations of $s$-wave pion production have severely underestimated
the accurately known $pp\rightarrow pp\pi^0$\ total cross section near
threshold. In these calculations, only the single-nucleon axial-charge operator
is considered. We have calculated, in addition to the one-body term, the
two-body contributions to this reaction that arise from the exchange of mesons.
We find that the inclusion of the scalar $\sigma$-meson exchange current (and
lesser contributions from other mesons) increases the cross section by about a
factor of five, and leads to excellent agreement with the data. The results are
neither very sensitive to changes in the distorting potential that generates
the $NN$ wave function, nor to different choices for the meson-nucleon form
factors. We argue that $pp\rightarrow pp\pi^0$\ data provide direct
experimental evidence for meson-exchange contributions to the axial current.


title: The Delta-Hole model at Finite Temperature

abstract:
  The spectral function of pions interacting with a gas of nucleons and
Delta-33-resonances is investigated using the formalism of Thermo Field
Dynamics. After a discussion of the zero Delta-width approximation at finite
temperature, we take into account a constant width of the resonance. Apart from
a full numerical calculation, we give analytical approximations to the pionic
spectral function including such a width. They are found to be different from
previous approximations, and require an increase of the effective Delta-width
in hot compressed nuclear matter. The results are summarized in an effective
dispersion relation for interacting pions.


title:
Diagonalization of full finite temperature Green's function by
  quasi-particles

abstract:
  For thermal systems, standard perturbation theory breaks down because of the
absence of stable, observable asymptotic states. We show, how the introduction
of {\it statistical} quasi-particles (stable, but not observable) gives rise to
a consistent description. Statistical and spectral information can be cleanly
separated also for interacting systems.


title: Chiral Baryon with Quantized Pions

abstract:
  We study a hybrid chiral model for the nucleon based on the linear sigma
model with explicit quarks. We solve the model using a Fock-space configuration
consisting of three quarks plus three quarks and a pion as the ground state
ansatz in place of the ``hedgehog'' ansatz. We minimize the expectation value
of the chiral hamiltonian in this ground state configuration and solve the
resulting equations for nucleon quantum numbers. We calculate the canonical set
of nucleon observables and compare with previous work.


title: Nuclear Flow Excitation Function

abstract:
  We consider the dependence of collective flow on the nuclear surface
thickness in a Boltzmann--Uehling--Uhlenbeck transport model of heavy ion
collisions. Well defined surfaces are introduced by giving test particles a
Gaussian density profile of constant width. Zeros of the flow excitation
function are as much influenced by the surface thickness as the nuclear
equation of state, and the dependence of this effect is understood in terms of
a simple potential scattering model. Realistic calculations must also take into
account medium effects for the nucleon--nucleon cross section, and impact
parameter averaging. We find that balance energy scales with the mass number as
$A^{-y}$, where $y$ has a numerical value between 0.35 and 0.5, depending on
the assumptions about the in-medium nucleon-nucleon cross section.


title:
Maximum Azimuthal Anisotropy of Neutrons from Nb-Nb Collisions at 400
  AMeV and the Nuclear Equation of State

abstract:
  We measured the first azimuthal distributions of triple--differential cross
sections of neutrons emitted in heavy-ion collisions, and compared their
maximum azimuthal anisotropy ratios with Boltzmann--Uehling--Uhlenbeck (BUU)
calculations with a momentum-dependent interaction. The BUU calculations agree
with the triple- and double-differential cross sections for positive rapidity
neutrons emitted at polar angles from 7 to 27 degrees; however, the maximum
azimuthal anisotropy ratio for these free neutrons is insensitive to the size
of the nuclear incompressibility modulus K characterizing the nuclear matter
equation of state.


title:
Model Analysis of Time Reversal Symmetry Test in the Caltech Fe-57
  Gamma-Transition Experiment

abstract:
  The CALTECH gamma-transition experiment testing time reversal symmetry via
the E2/M1 mulipole mixing ratio of the 122 keV gamma-line in Fe-57 has already
been performed in 1977. Extending an earlier analysis in terms of an effective
one-body potential, this experiment is now analyzed in terms of effective one
boson exchange T-odd P-even nucleon nucleon potentials. Within the model space
considered for the Fe-57 nucleus no contribution from isovector rho-type
exchange is possible. The bound on the coupling strength phi_A from effective
short range axial-vector type exchange induced by the experimental bound on
sin(eta) leads to phi_A < 10^{-2}.


title: Determination of Dipole Polarization Effects in $^7$Li and $^{11}$Li

abstract:
  The structure of $^6$Li, $^7$Li and $^{11}$Li nuclei is investigated in a
model space which includes all configurations with oscillator energy up to
$3\hbar\omega$ above the ground state configuration. The energy spectra and
electromagnetic properties of the low-lying states are determined with various
two-body interactions, which are derived from the Bonn potential. The results
of these shell-model calculations depend on the strength of the tensor
component contained in the NN interaction and also on the treatment of the
Dirac spinors for the nucleons in the nuclear medium. In addition the
calculation determines the {\it dipole polarizability} of $^7$Li and $^{11}$Li
caused from virtual $E1$ excitations to the positive parity states of these
nuclei. It is demonstrated that the BAGEL scheme provides a very powerful tool
to consider contributions from virtual excitations up to large energies.


title: Semi-Classical Description of Antiproton Capture on Atomic Helium

abstract:
  A semi-classical, many-body atomic model incorporating a momentum-dependent
Heisenberg core to stabilize atomic electrons is used to study antiproton
capture on Helium. Details of the antiproton collisions leading to eventual
capture are presented, including the energy and angular momentum states of
incident antiprotons which result in capture via single or double electron
ionization, i.e. into [He$^{++}\,\bar p$ or He$^{+}\,\bar p$], and the
distribution of energy and angular momentum states following the Auger cascade.
These final states are discussed in light of recently reported, anomalously
long-lived antiproton states observed in liquid He.


title: Electromagnetic Scattering from Relativistic Bound States

abstract:
  The quasipotential formalism for elastic scattering from relativistic bound
states is formulated based on the instant constraint in the Breit frame. The
quasipotential electromagnetic current is derived from Mandelstam's five-point
kernel and obeys a two-body Ward identity. Breit-frame wave functions are
obtained directly by solving integral equations with nonzero total
three-momentum, thus accomplishing a dynamical boost. Calculations of
electron-deuteron elastic form factors illustrate the importance of the
dynamical boost versus kinematic boosts of the rest frame wave functions.


title: Nucleon polarization in deuteron electrodisintegration

abstract:
  Outgoing nucleon polarization in exclusive deuteron electrodisintegration is
studied at the quasi-elastic peak in the standard theory with emphasis on the
effect of nucleonic and pionic relativistic corrections. The cases of polarized
beam or/and polarized target are considered. Sizeable relativistic effects are
pointed out in several polarization components. The sensitivity of nucleon
polarization to the neutron charge form factor $G_E^n$ is discussed. In
particular, it is shown that the longitudinal component of neutron polarization
with vector polarized deuterons is as sensitive to $G_E^n$ as the sideways beam
polarization transfer.


title: Colour transparency: a novel test of QCD in nuclear interactions

abstract:
  Colour transparency is a cute and indispensable property of QCD as the gauge
theory of strong interaction. CT tests of QCD consist of production of the
perturbative small-sized hadronic state and measuring the strngth of its
non-perturbative diffraction nteraction in a nuclear matter. The energy
depenednce of the final- state interaction in a nuclear matter probes a
dynamical evolution from the perturbative small-sized state to the full-sized
nonperturbative hadron. QCD observables of CT experiments correspond to a novel
mechanism of scanning of hadronic wave functions from the large nonperturbative
to the small perturbative size. In these lectures, which are addressed to
experimentalists and theorists, I discuss the principle ideas of CT physics and
the physics potential of the hadron and electron facilities in the > 10 GeV
energy range. The special effort was made to present the material in the
pedagigical and self-consistent way, with an emphasis on the underlying rich
quantum-mechanical interference phenomena.


title: Color Magnetic Corrections to Quark Model Valence Distributions

abstract:
  We calculate order $\alpha_s$ color magnetic corrections to the valence quark
distributions of the proton using the Los Alamos Model Potential wavefunctions.
The spin-spin interaction breaks the model SU(4) symmetry, providing a natural
mechanism for the difference between the up and down distributions. For a value
of $\alpha_s$ sufficient to produce the $N-\Delta$ mass splitting, we find up
and down quark distributions in reasonable agreement with experiment.


title:
Quasielastic neutrino scattering from oxygen and the atmospheric
  neutrino problem

abstract:
  We examine several phenomena beyond the scope of Fermi-gas models that affect
the quasielastic scattering (from oxygen) of neutrinos in the 0.1 -- 3.0 GeV
range. These include Coulomb interactions of outgoing protons and leptons, a
realistic finite-volume mean field, and the residual nucleon-nucleon
interaction. None of these effects are accurately represented in the Monte
Carlo simulations used to predict event rates due to $\mu$ and $e$ neutrinos
from cosmic-ray collisions in the atmosphere. We nevertheless conclude that the
neglected physics cannot account for the anomalous $\mu$ to $e$ ratio observed
at Kamiokande and IMB, and is unlikely to change absolute event rates by more
than 10--15\%. We briefly mention other phenomena, still to be investigated in
detail, that may produce larger changes.


title:
Electromagnetic Dipole Response as a Test of the $^{\bf 11}$Li g.s.
  Structure and the n-$^{\bf 9}$Li Interaction

abstract:
  The electric dipole response of the halo nucleus $^{11}$Li is calculated in a
hyperspherical three-body formulation, and is studied as a function of the
interaction employed for $n-^9$Li to reflect the Pauli principle. Strength
concentrations at lower energies are found but no narrow resonances. Only one
possible scenario of $^{11}$Li structure is in close correspondence with MSU
and RIKEN experimental data.


title:
Supershell Effect and Stability of Classical Periodic Orbits in
  Reflection-Asymmetric Superdeformed Oscillator

abstract:
  A semiclassical analysis is made of the origin of an undulating pattern in
the smoothed level density for a reflection-asymmetric superdeformed oscillator
potential. It is suggested that, when the octupole-type deformation increases,
an interference effect between two families of periodic orbit with the ratio of
periods approximately 2:1 becomes stronger and thus a pronounced ``supershell''
structure appears.


title:
No-Lose `Theorem' for Parity Violating Nucleon-Nucleon Scattering
  Experiments

abstract:
  A purely left-chiral model of the weak interactions is used to show that the
total parity-violating asymmetry in quark-quark scattering must grow with
increasing energy. In the absence of other new physics, non-observation of a
large asymmetry can therefore be used to infer an upper bound on the mass scale
for new right-chiral weak vector bosons. Applying this idea to actual
nucleon-nucleon scattering requires more involved calculations, as the dominant
contribution appears to come from a component of diquark-quark scattering
related to, but not identical to, wavefunction-mixing. Earlier criticism of
this model by Simonius and Unger is refuted and a new calculation is proposed
as an additional check on the result. Finally, we argue that the so-called
`spin crisis' does not affect our conclusions. (Talk given at the BNL workshop
on future directions in particle and nuclear physics at multi-GeV hadron beam
facilities, March 4--6, 1993.)


title: The Off Shell $\rho$-$\omega$ Mixing in the QCD Sum Rules

abstract:
  The $q^2$ dependence of the $\rho-\omega$ mixing amplitude is analyzed with
the use of the QCD sum rules and the dispersion relation. Going off shell the
mixing decreases, changes sign at $q^2 \simeq 0.4 m_{\rho}^2 > 0$ and is
negative in the space like region. Implications of this result to the isospin
breaking part of the nuclear force are discussed.


title:
Comment on "Comparison of Potential Models with the PP Scattering Data
  Below 350 Mev"

abstract:
  We point out two flaws in the recent test of nucleon-nucleon (NN) potentials
conducted by Stoks and de Swart. First, in some cases, the neutron-proton
($np$) version of an NN potential was compared to the proton-proton ($pp$)
data, which is improper and yields (large) $\chi^2$ that are essentially
meaningless. Second, for a proper test of the quantitative nature of a NN
potential, it is insufficient to compare to $pp$ data only, since this leaves
the T=0 potential untested. Thus, it can happen that the $pp$ version of a
potential predicts the $pp$ data accurately, while the $np$ version of that
same potential is poor in $np$ (where also the T=0 potential is involved). An
example for this is the Nijmegen potential, which predicts the $pp$ data well
with a $\chi^2$/datum of 2.0, but yields a $\chi^2$/datum of 6.5 in $np$.


title: Effects of Negative Energy Components in the Constituent Quark Model

abstract:
  Relativistic covariance requires that in the constituent quark model for
mesons the positive energy states as well as the negative energy states are
included. Using relativistic quasi-potential equations the contribution of the
negative energy states is studied for the light and charmonium mesons. It is
found that these states change the meson mass spectrum significantly but leave
its global structure untouched.


title: Approximate Particle Number Projection for Rotating Nuclei

abstract:
  Pairing correlations in rotating nuclei are discussed within the
Lipkin-Nogami method. The accuracy of the method is tested for the
Krumlinde-Szyma\'nski R(5) model. The results of calculations are compared with
those obtained from the standard mean field theory and particle-number
projection method, and with exact solutions.


title: Microscopic Calculations of the Spectra of Light Nuclei

abstract:
  We perform large-space shell-model calculations for the low-lying energy
spectra of a few light nuclei, $^4\mbox{He}$, $^5\mbox{He}$, $^6\mbox{Li}$ and
$^7\mbox{Li}$, in a no-core model space with a realistic effective two-body
interaction (Brueckner G-matrix). Our G-matrices are calculated for the
Reid-soft-core potential in a harmonic oscillator basis. Single-particle ``-U''
insertions are replaced by two-particle ``-U'' insertions and are included in
the G matrix calculations, which sum them to all orders. With the starting
energy of the G-matrix chosen to give approximately the experimental binding
energy, we obtain nuclear energy spectra which are in reasonable agreement with
experiment. We also investigate the dependence of our results on the size of
the model space and on the harmonic oscillator basis parameter ($\hbar\Omega$).


title: Localization of shadow poles by complex scaling

abstract:
  Through numerical examples we show that the complex scaling method is suited
to explore the pole structure in multichannel scattering problems. All poles
lying on the multisheeted Riemann energy surface, including shadow poles, can
be revealed and the Riemann sheets on which they reside can be identified.


title: Quark-based Description of Nuclear Matter with Simulated Annealing

abstract:
  We calculate ground-state properties of a many-quark system in the
string-flip model using variational Monte Carlo methods. The many-body
potential energy of the system is determined by finding the optimal grouping of
quarks into hadrons. This (optimal) assignment problem is solved by using the
stochastic optimization technique of simulated annealing. Results are presented
for the energy and length-scale for confinement as a function of density. These
results show how quarks clustering decreases with density and characterize the
nuclear- to quark-matter transition. We compare our results to a previously
published work with a similar model which uses, instead, a pairing approach to
the optimization problem.


title:
Thermal properties of a rotating nucleus in a fluctuating mean field
  approach

abstract:
  The static path approximation to the path integral representation of
partition function provides a natural microscopic basis to deal with thermal
fluctuations around mean field configurations.
  Using this approach for one-dimensional cranking Hamiltonian with quadrupole-
quadrupole interaction term we have studied a few properties like energy, level
density, level density parameter($a$) and moment of inertia as a function of
temperature and spin for $^{64}Zn$ taking it as an illustrative example. We
have also investigated the effects of variation in interaction strength on the
level density and the parameter $a$ as a function of temperature. The moment of
inertia, $\cal I$ versus rotational frequency, $\omega$ plot shows a sudden
rise in the value of $\cal I$ due to rotation alignment of $0g_{9/2}$ orbitals
at $\omega\approx 1.0$ MeV for a small temperature T $\sim 0.5$ MeV. At high T
$\sim$ 2.0 MeV about 40-45$\%$ of each angular momentum is generated by
alignment of $0g_{9/2}$ orbitals with an interesting result that at $\omega\sim
1.0$ MeV and spin J $\sim$ 16 the moment of inertia has almost a constant,
temperature independent value.


title: Neural Filters for Jet Analysis

abstract:
  We study the efficiency of a neural-net filter and deconvolution method for
estimating jet energies and spectra in high-background reactions such as
nuclear collisions at the relativistic heavy-ion collider and the large hadron
collider. The optimal network is shown to be surprisingly close but not
identical to a linear high-pass filter. A suitably constrained deconvolution
method is shown to uncover accurately the underlying jet distribution in spite
of the broad network response. Finally, we show that possible changes of the
jet spectrum in nuclear collisions can be analyzed quantitatively, in terms of
an effective energy loss with the proposed method. {} {Dong D W and Gyulassy M
1993}{Neural filters for jet analysis}
  {(LBL-31560) Physical Review E Vol~47(4) pp~2913-2922}


title: Vacuum Structures in Hamiltonian Light-Front Dynamics

abstract:
  Hamiltonian light-front dynamics of quantum fields may provide a useful
approach to systematic non-perturbative approximations to quantum field
theories. We investigate inequivalent Hilbert-space representations of the
light-front field algebra in which the stability group of the light-front is
implemented by unitary transformations. The Hilbert space representation of
states is generated by the operator algebra from the vacuum state. There is a
large class of vacuum states besides the Fock vacuum which meet all the
invariance requirements. The light-front Hamiltonian must annihilate the vacuum
and have a positive spectrum. We exhibit relations of the Hamiltonian to the
nontrivial vacuum structure.


title:
Composition, Structure and Evolution of Neutron Stars with Kaon
  Condensates

abstract:
  We investigate the possibility of kaon condensation in the dense interior of
neutron stars through the s--wave interaction of kaons with nucleons. We
include nucleon--nucleon interactions by using simple parametrizations of
realistic forces, and include electrons and muons in $\beta$--equilibrium. The
conditions under which kaon condensed cores undergo a transition to quark
matter containing strange quarks are also established. The critical density for
kaon condensation lies in the range (2.3--5.0)$~\rho_0$, where
$\rho_0=0.16$~fm$^{-3}$ is the equilibrium density of nuclear matter. For too
large a value of the strangeness content of the proton, matter with a kaon
condensate is not sufficiently stiff to support the lower limit of $1.44
M_\odot$ for a neutron star. Kaon condensation dramatically increases the
proton abundance of matter and even allows positrons to exist inside the core.
We also consider the case when neutrinos are trapped in the matter. Neutrino
trapping shifts both kaon condensation and the quark matter transition to
higher densities than in the case of cold, catalyzed matter. A newly--formed
neutron star is expected to have a rather low central density, the density
rising only after mass accretion onto the star ends after a few seconds. Thus,
it is likely that if kaon condensation and/or the quark--hadron phase
transition occur, they do so only during or after the mass accretion and
neutrino trapping stages. We suggest that neutrino observations from a galactic
supernova may provide direct evidence for or against a condensate and/or a
quark--hadron transition.


title:
The column vector calculus for Thermo Field Dynamics of relativistic
  quantum fields

abstract:
  A formalism is discussed which simplifies the calculation of Feynman diagrams
at finite temperature.


title: Effective Kaon Mass in Baryonic Matter and Kaon Condensation

abstract:
  The effective kaon mass in dense baryonic matter is calculated based on PCAC,
current algebra and the Weinberg smoothness hypothesis. The off-shell behavior
of the K-N scattering amplitudes is treated consistently with PCAC, and the
effects of the subthreshold K-N resonances are also included. The effective
kaon mass is found to depend crucially on the K-N sigma term. Since the current
estimates of K-N Sigma term are very uncertain, we discuss various scenarios
treating K-N Sigma term as an input parameter; for certain values of K-N Sigma
a collective mode of a hyperon-particle-nucleon-hole state appears at high
densities, possibly leading to kaon condensation.


title: Monte Carlo evaluation of path integrals for the nuclear shell model

abstract:
  We present in detail a formulation of the shell model as a path integral and
Monte Carlo techniques for its evaluation. The formulation, which linearizes
the two-body interaction by an auxiliary field, is quite general, both in the
form of the effective `one-body' Hamiltonian and in the choice of ensemble. In
particular, we derive formulas for the use of general (beyond monopole) pairing
operators, as well as a novel extraction of the canonical (fixed-particle
number) ensemble via an activity expansion. We discuss the advantages and
disadvantages of the various formulations and ensembles and give several
illustrative examples. We also discuss and illustrate calculation of the
imaginary-time response function and the extraction, by maximum entropy
methods, of the corresponding strength function. Finally, we discuss the
"sign-problem" generic to fermion Monte Carlo calculations, and prove that a
wide class of interactions are free of this limitation.


title: Relativistic meson spectroscopy

abstract:
  In this paper a relativistic quantum theory introduced by de Groot and
\mbox{Ruijgrok} in 1975, is used as a quark model in momentum space. The
complete spectrum, with the exception of the selfconjugate light unflavoured
mesons, is calculated. The potential used consists of an one-gluon-exchange
(OGE) part and a confining part. For the confining part a relativistic
generalization of the linear plus constant potential was used, which is
well-defined in momentum space without introducing any singularities. For the
OGE part several potentials were investigated. Retardations were included at
all places. Using a fitting procedure involving 52 well-established mesons,
best results were obtained for a potential consisting of a purely vector
Richardson potential and a purely scalar confining potential. In this way a
vector confining is entirely induced by the Richardson potential. Reasonable
results were also obtained for a modified Richardson potential. Most meson
masses, with the exception of the $\pi$, the $K$ and the $K_0^*$, were found to
be reasonably well described by the model.


title: A Theorem on Light-Front Quantum Models

abstract:
  I give a sufficient condition for a relativistic front-form quantum
mechanical model to be scattering equivalent (unitarily equivalent with the
same S-matrix elements) to a relativistic front-form quantum model with an
interaction-independent front-form spin.


title:
Collective Dipole Oscillations in Atomic Nuclei and Small Metal
  Particles

abstract:
  (The systematics of photon absorption cross sections in nuclei and small
metal particles are examined as a function of the number of constituent
fermions $A$. It is pointed out that the shell-structure-linked oscillations in
the full width at half maximum (FWHM) of the photoneutron cross section in
nuclei, earlier recognized for $A > 63$, in fact persist down to the lightest
nuclei. Averaging over the oscillations or focusing on the lower envelope of
the oscillating curve (magic nuclei), the FWHM is seen to generally decrease
with increasing $A$, consistent with $A^{-1/3}$, a dependence which was earlier
known to hold in metal particle systems. If the FWHMs are scaled by the
respective Fermi energies and the inverse radii by the Fermi wave vectors, the
two data sets become comparable in magnitude. A schematic theoretical
description of the systematics is presented.)


title: Proof of stability of the hydrogen molecule

abstract:
  We sketch two rigorous proofs of the stability of the hydrogen molecule in
quantum mechanics. The first one is based on an extrapolation of variational
estimates of the groundstate energy of a positronium molecule to arbitrary mass
ratios. The second one is an extension of Heitler-London theory to nuclei of
finite mass.


title:
Three-Nucleon Force and the $\Delta$-Mechanism for Pion Production and
  Pion Absorption

abstract:
  The description of the three-nucleon system in terms of nucleon and $\Delta$
degrees of freedom is extended to allow for explicit pion production
(absorption) from single dynamic $\Delta$ de-excitation (excitation) processes.
This mechanism yields an energy dependent effective three-body hamiltonean. The
Faddeev equations for the trinucleon bound state are solved with a force model
that has already been tested in the two-nucleon system above pion-production
threshold. The binding energy and other bound state properties are calculated.
The contribution to the effective three-nucleon force arising from the pionic
degrees of freedom is evaluated. The validity of previous coupled-channel
calculations with explicit but stable $\Delta$ isobar components in the
wavefunction is studied.


title: Temperature induced alignment in hot rotating nuclei

abstract:
  Employing a cranking Hamiltonian, in the static path approximation to the
partition function, we have studied the behaviour of the moment of inertia of
$^{64}Zn$ at a few values of temperatures as a function of the rotation
frequency. At a low temperature T = 0.5 MeV and J=16 rotational alignment of
$0g_{9/2}$ orbitals takes place. But at a high temperature T = 2.0 MeV about 40
- 45$\%$ of all the angular momenta are generated by the alignment of the same
orbitals. This should imply a decrease in collectivity for all the spins at
high temperatures.


title:
Quantum Interference Effects in N* Electroproduction and Propagation in
  Nuclei

abstract:
  We discuss the unexpected enhancement of the $N^*$ electroproduction on
nuclei recently observed in the $(\gamma^*,p\pi^-)$ measurement. A mechanism
which is able to explain this result is proposed. To clarify the situation, we
suggest to perform a new kind of experiment within well specified kinematic
conditions.


title: Momentum and Coordinate Space Three-nucleon Potentials

abstract:
  In this paper we give explicit formulae in momentum and coordinate space for
the three-nucleon potentials due to $\rho$ and $\pi$ meson exchange, derived
from off-mass-shell meson-nucleon scattering amplitudes which are constrained
by the symmetries of QCD and by the experimental data. Those potentials have
already been applied to nuclear matter calculations. Here we display additional
terms which appear to be the most important for nuclear structure. The
potentials are decomposed in a way that separates the contributions of
different physical mechanisms involved in the meson-nucleon amplitudes. The
same type of decomposition is presented for the $\pi - \pi$ TM force: the
$\Delta$, the chiral symmetry breaking and the nucleon pair terms are isolated.


title: From Skyrmions to NN phaseshifts

abstract:
  We study the $NN$ phaseshifts in a Hamiltonian obtained from quantization of
the collective modes in the Skyrme model. We show that a combination of an
adiabatic and diabatic approximation gives a good $NN$ force, with sufficient
attraction to produce a bound deuteron. The description of the repulsive core
appears to be the main cause for the remaining discrepancies between the Skyrme
model force and phenomenology. Finally we discuss the possibility of finding
non-strange dibaryon resonances in the $J^\pi=3^+$ channel.


title: Hamiltonian Dynamics of Yang-Mills Fields on a Lattice

abstract:
  We review recent results from studies of the dynamics of classical Yang-Mills
fields on a lattice. We discuss the numerical techniques employed in solving
the classical lattice Yang-Mills equations in real time, and present results
exhibiting the universal chaotic behavior of nonabelian gauge theories. The
complete spectrum of Lyapunov exponents is determined for the gauge group
SU(2). We survey results obtained for the SU(3) gauge theory and other
nonlinear field theories. We also discuss the relevance of these results to the
problem of thermalization in gauge theories.


title: Multiple Collisions and Induced Gluon Bremsstrahlung in QCD

abstract:
  Induced soft gluon bremsstrahlung associated with multiple collisions is
calculated via perturbative QCD. We derive the non-abelian analog of the
Landau-Pomeranchuk effect that suppresses induced soft radiation with formation
times exceeding the mean free path, $\lambda$. The dependence of the
suppression effect on the $SU(N)$ representation of the jet parton as well as
the kinematic variables is expressed through a radiation formation factor.
Unlike in QED, the finite contribution from the small $x$ regime in QCD leads
to an approximately constant radiative energy loss per unit length,
$dE/dz\propto \mu^2$, in the high energy limit that is sensitive to the
infrared screening scale, $\mu$, of the medium. As a function of the
dimensionless parameter $\zeta=\lambda \mu^2/E$, we show furthermore how the
energy dependence of $dE/dz$ evolves from the above constant for $\zeta\ll 1$
to the more familiar (Bethe-Heitler) linear dependence for $\zeta \gg 1$.


title:
Dilepton Production in Nucleon-Nucleon Reactions With and Without
  Hadronic Inelasticities

abstract:
  We calculate elementary proton-proton and neutron-proton bremsstrahlung and
their contribution to the $e^+e^-$ invariant mass distribution. At 4.9 GeV, the
proton-proton contribution is larger than neutron-proton, but it is small
compared to recent data. We then make a first calculation of bremsstrahlung in
nucleon-nucleon reactions with multi-hadron final states. Again at 4.9 GeV, the
many-body bremsstrahlung is larger than simple nucleon-nucleon bremsstrahlung
by more than an order of magnitude in the low-mass region. When the
bremsstrahlung contributions are summed with Dalitz decay of the $\eta$,
radiative decay of the $\Delta$ and from two-pion annihilation, the result
matches recent high statistics proton-proton data from the Dilepton
Spectrometer collaboration.


title:
Alpha scattering and capture reactions in the A = 7 system at low
  energies

abstract:
  Differential cross sections for $^3$He-$\alpha$ scattering were measured in
the energy range up to 3 MeV. These data together with other available
experimental results for $^3$He $+ \alpha$ and $^3$H $+ \alpha$ scattering were
analyzed in the framework of the optical model using double-folded potentials.
The optical potentials obtained were used to calculate the astrophysical
S-factors of the capture reactions $^3$He$(\alpha,\gamma)^7$Be and
$^3$H$(\alpha,\gamma)^7$Li, and the branching ratios for the transitions into
the two final $^7$Be and $^7$Li bound states, respectively. For
$^3$He$(\alpha,\gamma)^7$Be excellent agreement between calculated and
experimental data is obtained. For $^3$H$(\alpha,\gamma)^7$Li a $S(0)$ value
has been found which is a factor of about 1.5 larger than the adopted value.
For both capture reactions a similar branching ratio of $R =
\sigma(\gamma_1)/\sigma(\gamma_0) \approx 0.43$ has been obtained.


title: Simple relativistic model of a finite-size particle

abstract:
  Soluble model of a relativistic particle describing a bag of matter with
fixed radius held together in perfect balance by a self-consistent combination
of three forces generated by electromagnetic and massive scalar and vector
fields is presented. For realistic values of parameters the bag radius becomes
that of a proton.


title:
Correlation Effects in the Final-State Interaction for Quasielastic
  $(e,e'p)$ Scattering

abstract:
  Color transparency predicts that, in $(e,e'p)$ reactions at large $Q^2$, the
final-state interaction becomes weaker than the reference value predicted from
the free-nucleon cross section. This reference value is usually evaluated in
the dilute-gas approximation to Glauber's multiple-scattering theory. We derive
the leading-order correction taking into account two-body correlations. Large
cancellations are found so that the overall correlation effect is small.


title: Non-Linear Mean Field Dynamics in the Nuclear Spinodal Zone

abstract:
  We demonstrate, by numerical simulations, that the dynamics of nuclear matter
mean field inside the spinodal region is chaotic. Spontaneous symmetry-breaking
- no explicit fluctuating term is considered - occurs leading to wild
unpredictable density fluctuations. A proper recipe to calculate an average
Lyapunov exponent in this multidimensional phase space is introduced. The
latter is calculated for different values of the density in order to
characterize in a quantitative way the chaotic and regular regions. It is
argued that the mean field chaoticity can be the main mechanism of the nuclear
multifragmentation occurring in the intermediate energy reactions.


title: Relativistic three-particle scattering equations

abstract:
  We derive a set of relativistic three-particle scattering equations in the
three-particle c.m. frame employing a relativistic three-particle propagator
suggested long ago by Ahmadzadeh and Tjon in the c.m. frame of a two-particle
subsystem. We make the coordinate transformation of this propagator from the
c.m. frame of the two-particle subsystem to the three-particle c.m. frame. We
also point out that some numerical applications of the Ahmadzadeh and Tjon
propagator to the three-nucleon problem use unnecessary nonrelativistic
approximations which do not simplify the computational task, but violate
constraints of relativistic unitarity and/or covariance.


title: Exact response of the non-relativistic harmonic oscillator

abstract:
  Using Green$'$s function and operator techniques we give a closed expression
for the response of a non-relativistic system interacting through confining,
harmonic forces. The expression for the incoherent part permits rapid
evaluation of coefficients in a 1/q expansion. A comparison is made with
standard approximation methods.


title: Levinson's Theorem for Dirac Particles

abstract:
  Levinson's theorem for Dirac particles constraints the sum of the phase
shifts at threshold by the total number of bound states of the Dirac equation.
Recently, a stronger version of Levinson's theorem has been proven in which the
value of the positive- and negative-energy phase shifts are separately
constrained by the number of bound states of an appropriate set of
Schr\"odinger-like equations. In this work we elaborate on these ideas and show
that the stronger form of Levinson's theorem relates the individual phase
shifts directly to the number of bound states of the Dirac equation having an
even or odd number of nodes. We use a mean-field approximation to Walecka's
scalar-vector model to illustrate this stronger form of Levinson's theorem. We
show that the assignment of bound states to a particular phase shift should be
done, not on the basis of the sign of the bound-state energy, but rather, in
terms of the nodal structure (even/odd number of nodes) of the bound state.


title: Dirac sea effects in $K^+$ scattering from nuclei

abstract:
  The ratio $R_T$ of $K^+-^{12}C$ to $K^+-d$ cross sections has been calculated
microscopically using a boson-exchange $KN$ amplitude in which the $\sigma$ and
$\omega$ mesons are dressed by the modifications of the Dirac sea in nuclear
matter. In spite of the fact that this dressing leads to a scaling of the
mesons effective mass in nuclear matter, the effect on the $R_T$ ratio is found
to be weak.


title: Generalized transparency in semi-inclusive processes

abstract:
  It is argued that the transparency of a medium for passage of a nucleon,
knocked-out in a semi-inclusive $(e,e'p)$ reaction and subsequently scattered
elastically, is not the same as the one measured in purely elastic scattering.
Expressions are given for the properly generalized transparency and those are
compared with recently proposed, alternative suggestions. Numerical results are
presented for selected nuclear targets and kinematic conditions, applying to
the Garino et al and the SLAC NE18 experiment.


title: Minimizing Effective Many-Body Interactions

abstract:
  A simple two-level model is developed and used to test the properties of
effective interactions for performing nuclear structure calculations in
truncated model spaces. It is shown that the effective many-body interactions
sensitively depend on the choice of the single-particle basis and they appear
to be minimized when a self- consistent Hartree-Fock basis is used.


title: Exotic Heavy Baryons at LHC?

abstract:
  We speculate about a heavy bottom-charm six-quark baryon. A semiclassical and
a gaussian estimate reveal that the octet-octet bbb-ccc configuration can be
energetically favored with respect to the singlet-singlet one. This result
suggests that a confined bbb-ccc six-quark state may exist. Such objects may be
produced in appreciable amount in heavy ion collisions at LHC energies.


title: Selfconsistent Description of a Thermal Piongas

abstract:
  We examine a hot pion gas by including medium modifications of the two-body
scattering amplitude as well as mean-field effects selfconsistently. In
contrast to earlier calculations, the in-medium T-matrix is rather close to the
free one while the mean-field potential agrees well with lowest-order
estimates. We also discuss the validity of the quasiparticle approximation. It
is found that it is reliable for temperatures up to $\sim 150$ MeV. Above this
temperature off-shell effects in the pion selfenergy become important,
especially if the pions are strongly out of chemical equilibrium.


title: Thermo Field Dynamics and Kinetic Coefficients of a Charged Boson Gas

abstract:
  Thermo Field Dynamics for inhomogeneous systems is generalized to quantum
fields with a continuous single-particle mass spectrum. The modification of the
hamiltonian in states with a local thermal Bogoliubov symmetry is used to
calculate thermal conductivity and diffusion coefficient of pions interacting
with hot, compressed nuclear matter.


title: Algebraic Treatment of Collective Excitations in Baryon Spectroscopy

abstract:
  We present an algebraic U(7) model for baryons which encompasses both
single-particle and collective forms of quark dynamics. The mass operator by
construction preserves the permutation symmetry between identical quarks. The
underlying geometric structure of baryons is discussed in terms of a rigid
rotating and vibrating oblate top shape. The model is applied to the mass
spectrum of nonstrange baryons.


title: Charge-Symmetry Breaking, Rho-Omega Mixing and the Quark Propagator

abstract:
  The momentum-dependence of the $\rho^0$-$\omega$ mixing contribution to
charge-symmetry breaking (CSB) in the nucleon-nucleon interaction is compared
in a variety of models. We focus in particular on the role that the structure
of the quark propagator plays in the predicted behaviour of the
$\rho^0$-$\omega$ mixing amplitude. We present new results for a confining
(entire) quark propagator and for typical propagators arising from explicit
numerical solutions of quark Dyson-Schwinger equations. We compare these to
hadronic and free quark calculations. The implications for our current
understanding of CSB experiments is discussed.


title:
Antiproton Production in p-Nucleus and Nucleus-Nucleus Collisions within
  a Relativistic Transport Approach

abstract:
  The production of antiprotons in proton-nucleus and nucleus-nucleus reactions
is calculated within the relativistic BUU approach employing proper
selfenergies for the baryons and antiprotons and treating the p-bar
annihilation nonperturbatively. The differential cross section for the
antiprotons is found to be very sensitive to the p-bar selfenergy adopted. A
detailed comparison with the available experimental data for p-nucleus and
nucleus-nucleus reactions shows that the antiproton feels a moderately
attractive mean-field at normal nuclear matter density which is in line with a
dispersive potential extracted from the free annihilation cross section.


title: A Quark Transport Theory to describe Nucleon--Nucleon Collisions

abstract:
  On the basis of the Friedberg-Lee model we formulate a semiclassical
transport theory to describe the phase-space evolution of nucleon-nucleon
collisions on the quark level. The time evolution is given by a Vlasov-equation
for the quark phase-space distribution and a Klein-Gordon equation for the
mean-field describing the nucleon as a soliton bag. The Vlasov equation is
solved numerically using an extended testparticle method. We test the
confinement mechanism and mean-field effects in 1+1 dimensional simulations.


title:
Iterative Solution for Effective Interactions in a System with
  Non-degenerate Unperturbed Energies

abstract:
  We generalize the Lee-Suzuki iteration method for summing the folded diagram
series to the case where the unperturbed model-space energies are
non-degenerate. A condition is derived for the convergence of the iteration
scheme and this depends on the choice of the model space projection operators.
Two choices are examined, in the first the projection operators are defined in
terms of the unperturbed states and in the second they are defined in terms of
the eigenfunctions obtained at each stage of the iteration. As is illustrated
by calculations with a simple model, the second procedure gives the better
convergence and, by suitable choice of the starting energies, allows the
reproduction of any subset of the exact eigenvalues.


title:
Microscopic multicluster description of neutron-halo nuclei with a
  stochastic variational method

abstract:
  To test a multicluster approach for halo nuclei, we give a unified
description for the ground states of $^6$He and $^8$He in a model comprising an
$\alpha$ cluster and single-neutron clusters. The intercluster wave function is
taken a superposition of terms belonging to different arrangements, each
defined by a set of Jacobi coordinates. Each term is then a superposition of
products of gaussian functions of the individual Jacobi coordinates with
different widths, projected to angular momenta $l=0$ or 1. To avoid excessively
large dimensions and ``overcompleteness", stochastic methods were tested for
selecting the gaussians spanning the basis. For $^6$He, we were able to
calculate ground-state energies that are virtully exact within the subspace
defined by the arrangements and $l$ values, and we found that preselected
random sets of bases (with or without simulated annealing) yield excellent
numerical convergence to this ``exact" value with thoroughly truncated bases.
For $^8$He good energy convergence was achieved in a state space comprising
three arrangements with all $l=0$, and there are indications showing that the
contributions of other subspaces are likely to be small. The $^6$He and $^8$He
energies are reproduced by the same effective force very well, and the matter
radii obtained are similar to those of other sophisticated calculations.


title: A Collective Model of Baryons

abstract:
  We propose an algebraic description of the geometric structure of baryons in
terms of the algebra $U(7)$. We construct a mass operator that preserves the
threefold permutational symmetry and discuss a collective model of baryons with
the geometry of an oblate top.


title: Proton halo of $^8$B in a microscopic model

abstract:
  The experimentally predicted existence of a proton halo in $^8$B is confirmed
by dynamical microscopic multiconfiguration cluster model calculations. The
thickness of the proton halo in $^8$B is 0.5 $fm$ while in $^8$Li a 0.4 $fm$
thick neutron halo has been found. It is shown that the huge quadrupole moment
of $^8$B partly comes from the very distortable $^7$Be core.


title: Improved Coupled Channels and R-Matrix Models: Predictions to 1 Gev

abstract:
  The $NN$ scattering near inelastic threshold is sensitive to the long-range
diagonal interaction in the produced isobar channel. Earlier models included
meson exchange potentials in the $NN$ sector and connecting that sector to
isobar channels, as well as an $R$-matrix description of short-range quark
effects. Including the diagonal pion exchange contributions in the $N\Delta$
channels coupled to the very inelastic ${}^1D_2$ and ${}^3F_3$ $NN$ channels
substantially improves those phase parameters and the observables
$\Delta\sigma_{L}$ and $\Delta\sigma_{T}$. The same improvement is made to the
other $I=1$ $NN$ channels. In the ${}^1S_0$ $NN$ channel coupling to the
$\Delta\Delta$ channel is unusually important due to the $L=2$ angular momentum
barrier in the $N\Delta$ channel. The pion exchange transition potentials
between isobar channels are included in this partial wave to obtain the correct
equilibrium between one- and two-pion decay channels. Other improvements to
earlier models have been made, in the specification of isobar channels and the
inclusion of decay width effects in more channels. A comparison is made with
all the $pp$ data for $T_L \le 800$~MeV, producing a very good fit over the
whole energy range.


title: A Full $PF$ Shell Model Study of a~=~48 Nuclei

abstract:
  Exact diagonalizations with a minimally modified realistic force lead to
detailed agreement with measured level schemes and electromagnetic transitions
in $^{48}$Ca, $^{48}$Sc, $^{48}$Ti, $^{48}$V, $^{48}$Cr and $^{48}$Mn.
Gamow-Teller strength functions are systematically calculated and reproduce the
data to within the standard quenching factor. Their fine structure indicates
that fragmentation makes much strength unobservable. As a by-product, the
calculations suggest a microscopic description of the onset of rotational
motion. The spectroscopic quality of the results provides strong arguments in
favour of the general validity of monopole corrected realistic forces, which is
discussed.


title: Absorption mechanisms in photon induced two-body knockout

abstract:
  Calculations have been performed for the $^{16}$O($\gamma$,pn) and the
$^{16}$O($\gamma$,pp) reaction in the photon-energy range $E_{\gamma}$ = 60-300
MeV. Besides the contribution from the more common photoabsorption on the
pionic degrees of freedom, we have investigated the influence of heavier meson
exchange ($\rho, \sigma, \omega$) and intermediate $\Delta$ creation with $\pi$
and $\rho$ exchange. Whereas the $\pi$ meson is found to set the main trends,
the $\rho$ meson is found not to be discardable in a theoretical description of
the ($\gamma$,pn) reaction. The incorporation of an energy dependence and a
decay width in the $\Delta$ propagator is observed to be essential in order to
arrive at a more realistic description of ($\gamma$,NN) reactions at higher
photon energies.


title: The Single-Particle Spectral Function of $^{16}{\rm O}$

abstract:
  The influence of short-range correlations on the $p$-wave single-particle
spectral function in $^{16}{\rm O}$ is studied as a function of energy. This
influence, which is represented by the admixture of high-momentum components,
is found to be small in the $p$-shell quasihole wave functions. It is therefore
unlikely that studies of quasihole momentum distributions using the $(e,e'p)$
reaction will reveal a significant contribution of high momentum components.
Instead, high-momentum components become increasingly more dominant at higher
excitation energy. The above observations are consistent with the energy
distribution of high-momentum components in nuclear matter.


title:
Effects of the final-state interaction in ($\gamma$,pn) and
  ($\gamma$,pp) processes

abstract:
  A model is presented to describe electromagnetically induced two-nucleon
emission processes in a shell-model picture. Distortions in the outgoing
nucleon waves are accounted for by performing a partial-wave expansion in a
real mean-field potential. The antisymmetry condition for the A-body
wavefunctions is shown to be naturally preserved.
  The model is used to calculate ($\gamma$,pn) and ($\gamma$,pp) cross sections
off the target nuclei $^{16}$O and $^{12}$C for photon energies ranging from 50
MeV up to the $\bigtriangleup$(1232) isobar threshold. Effects due to the
pionic currents and intermediate $\bigtriangleup$ creation are implemented. The
impact of the distortions due to the interaction of the outgoing nucleon waves
with the (A-2) core is examined. Hadronic form factors are introduced to
regularize the $\pi$NN vertices and the sensitivity of the cross section to the
pion cut-off mass is examined. The relative contribution of the ($\gamma$,pp)
and the ($\gamma$,pn) channel to the total photoabsorption strength is
discussed. Further, the photon energy dependence of the
($\gamma$,pp)/($\gamma$,pn) ratio is investigated.


title: Mean Field Approximation to two-subsystems: Examples

abstract:
  Using the Funtional Integrals Formulation is developes a self-consistent mean
field expansion to evolution operators of a system composed by two subsystems.
This is a general expansion and can be generalized for more of two subsystems,
which can be as system composed by fermions and bosons with an interaction
between their ($\sigma$-model , $\sigma-\omega$ model or maser model) as a
fermionic system with two or more different interactions between fermions
particles, (NJL model ).


title:
Neutron Stars and Nuclei in the Modified Relativistic Hartree
  Approximation

abstract:
  We have examined the properties of neutron-rich matter and finite nuclei in
the modified relativistic Hartree approximation for several values of the
renormalization scale, $\mu$, around the standard choice of $\mu$ equal to the
nucleon mass $M$. Observed neutron star masses do not effectively constrain the
value of $\mu$. However for finite nuclei the value $\mu/M=0.79$, suggested by
nuclear matter data, provides a good account of the bulk properties with a
sigma mass of about 600 MeV. This value of $\mu/M$ renders the effective three
and four body scalar self-couplings to be zero at 60\% of equilibrium nuclear
matter density, rather than in the vacuum. We have also found that the matter
part of the exchange diagram has little impact on the bulk properties of
neutron stars.


title: Color Diffusion and Conductivity in a Quark-Gluon Plasma

abstract:
  Color diffusion is shown to be an important dissipative property of
quark-gluon plasmas that rapidly damps collective color modes. We derive the
characteristic color relaxation time scale, $t_c\approx (3\alpha_s T
\log(m_E/m_M ))^{-1}$, showing its sensitivity to the ratio of the static color
electric and magnetic screening masses. This leads to a surprisingly small
color conductivity, $\sigma_c\approx 2 T/\log(m_E/m_M)$, which in fact vanishes
in the semi-classical (1-loop) limit.


title: Pion-nucleus reactions in a microscopic transport model

abstract:
  We analyse pion-nucleus reactions in a microscopic transport model of the BUU
type, which propagates nucleons, pions, deltas and N(1440)-resonances
explicitly in space and time. In particular we examine pion absorption and
inelastic scattering cross sections for pion kinetic energies T(pi) =85-315MeV
and various target masses. In general, the mass-dependence of the experimental
data is well described for energies up to the delta-resonance (\approx 160 MeV)
while the absorption cross sections are somewhat overestimated for the higher
energies. In addition we study the possible dynamical effects of delta- and
pion-potentials in the medium on various observables as well as alternative
models for the in-medium delta-width.


title:
Self-consistent solution of the Schwinger-Dyson equations for the
  nucleon and meson propagators

abstract:
  The Schwinger-Dyson equations for the nucleon and meson propagators are
solved self-consistently in an approximation that goes beyond the Hartree-Fock
approximation. The traditional approach consists in solving the nucleon
Schwinger-Dyson equation with bare meson propagators and bare meson-nucleon
vertices; the corrections to the meson propagators are calculated using the
bare nucleon propagator and bare nucleon-meson vertices. It is known that such
an approximation scheme produces the appearance of ghost poles in the
propagators. In this paper the coupled system of Schwinger-Dyson equations for
the nucleon and the meson propagators are solved self-consistently including
vertex corrections. The interplay of self-consistency and vertex corrections on
the ghosts problem is investigated. It is found that the self-consistency does
not affect significantly the spectral properties of the propagators. In
particular, it does not affect the appearance of the ghost poles in the
propagators.


title: Triton calculations with the new Nijmegen potentials

abstract:
  Triton properties are calculated using new nucleon-nucleon potentials, which
were fit to the world nucleon-nucleon data. All potentials are charge dependent
and explicitly incorporate the mass difference between the charged and neutral
pions. Three of these models have a nearly optimal chi**2 per degree of freedom
and can therefore be considered as alternative partial wave analyses, which in
quality can almost compete with the Nijmegen partial-wave analysis. The triton
binding energy obtained with three local models (Nijm II, Reid93, AV18) can be
summarized as 7.62 +_ 0.01 MeV, which is nearly 900 keV lower than experiment.
The non-local model Nijm I binds by 7.72 MeV.


title:
Space-time Structure of Initial Parton Production in Ultrarelativistic
  Heavy Ion Collisions

abstract:
  The space and time evolution of initial parton production in
ultrarelativistic heavy ion collisions is investigated within the framework of
perturbative QCD which includes both initial and final state radiations.
Uncertainty principle is used to relate the life time of a radiating parton to
its virtuality and momentum. The interaction time of each hard or semihard
parton scattering is also taken into account. For central $Au+Au$ collisions at
$\sqrt{s}=200$ GeV, most of the partons are found to be produced within 0.5
fm/c after the total overlap of the two colliding nuclei. The local momentum
distribution is approximately isotropical at that time. The implication on how
to treat correctly the the secondary scattering in an ultimate parton cascading
model is also discussed.


title:
Effects of meson-exchange currents on the $(\protect\vec{e},e'p)$
  structure functions

abstract:
  The response functions for the unpolarized $(e,e'p)$ and polarized
$(\vec{e},e'p)$ reaction are calculated for medium-heavy nuclei under quasifree
conditions. The formalism presented here incorporates two-body currents related
to meson-exchange and the $\Delta (1232)$ excitation. The final-state
interaction of the outgoing nucleon with the residual nucleus is handled in a
HF-RPA formalism. The sensitivity of the results to the two-body currents is
discussed for the five structure functions in quasielastic $(\vec{e},e'p)$
scattering off the target nuclei $^{16}O$ and $^{40}Ca$. A selective
sensitivity to the two-body currents is obtained in the longitudinal-transverse
interference term $W_{LT}$ where two-body currents can explain part of the
discrepancy between the impulse-approximation calculations and the data.