title: Thermal photon production in high-energy nuclear collisions

abstract:
  We use a boost-invariant one-dimensional (cylindrically symmetric) fluid
dynamics code to calculate thermal photon production in the central rapidity
region of S+Au and Pb+Pb collisions at SPS energy ($\sqrt{s}=20$ GeV/nucleon).
We assume that the hot matter is in thermal equilibrium throughout the
expansion, but consider deviations from chemical equilibrium in the high
temperature (deconfined) phase. We use equations of state with a first-order
phase transition between a massless pion gas and quark gluon plasma, with
transition temperatures in the range $150 \leq T_c \leq 200$ MeV.


title: Threshold Photo/Electro Pion Production - Working Group Summary

abstract:
  We summarize the pertinent experimental and theoretical developments in the
field of pion photo- and electroproduction in the threshold region. We discuss
which experiments and which calculations should be done/performed in the
future.


title: Time Invariant Scaling in Discrete Fragmentation Models

abstract:
  Linear rate equations are used to describe the cascading decay of an initial
heavy cluster into fragments. We consider moments of arbitrary orders of the
mass multiplicity spectrum and derive scaling properties pertaining to their
time evolution. We suggest that the mass weighted multiplicity is a suitable
observable for the discovery of scaling. Numerical tests validate such
properties, even for moderate values of the initial mass (nuclei, percolation
clusters, jets of particles etc.). Finite size effects can be simply
parametrized.


title:
Pushing and Cranking Corrections to the Meson Fields of the Bosonized
  Nambu \& Jona-Lasinio Model

abstract:
  We study the effect of center-of-mass motion and rotational corrections on
hedgehog meson fields in the bosonized two-flavor Nambu \& Jona-Lasinio model.
To remove the spurious motion and to restore good spin and isospin we consider
a boosted and rotating soliton instead a static soliton at rest. Modified meson
fields are obtained by minimizing a corrected effective energy functional. The
importance of the modification is estimated by evaluating expectation values of
several observables. Stabile solitonic configurations are obtained for $M\gapp$
300\,MeV, while static solitons exists for $M\gapp$ 350\,MeV only. Despite the
considerable size of the energy corrections (30-50\% of the soliton energy) the
main features of the static soliton are preserved. Modified meson profiles are
somewhat narrower than static ones and have a different asymptotic behavior,
which depends on the isospin quantum number. The modifications increase with
increasing constituent quark mass. The valence-quark picture dominates up to
very large constituent quark masses. In the physically relevant mass region,
the root-mean square radius of the quark distribution is reduced by less than
10 percent. The $\Delta$--nucleon mass-splitting is still weaker affected.


title: Pion-Nucleon and Kaon-Nucleon Scattering Lengths in QCD Sum Rules

abstract:
  The pion-nucleon and kaon-nucleon scattering lengths are studied in the QCD
sum rule. We show that the leading and next-to-leading order terms of the OPE
give rise to the Tomozawa-Weinberg and sigma terms, respectively. We also show
that in the kaon-nucleon system the $\Lambda(1405)$ contribution has to be
subtracted from the OPE side in order to obtain the scattering length. The odd
components of the $T$-matrices are in agreement with the experimental values
not only in the pion-nucleon channel but also in the kaon-nucleon channel after
the $\Lambda(1405)$ contribution subtracted. The even components disagree with
the experimental values in the pion-nucleon channel, which is similar to the
situation in the PCAC-plus-current-algebra approach at the Weinberg point. We
speculate that this discrepancy should be explained by the continuum
contribution in the spectral function above the pion-nucleon threshold.


title: Charge Independence and Charge Symmetry

abstract:
  Charge independence and charge symmetry are approximate symmetries of nature,
violated by the perturbing effects of the mass difference between up and down
quarks and by electromagnetic interactions. The observations of the symmetry
breaking effects in nuclear and particle physics and the implications of those
effects are reviewed.


title: Final state interaction effects in $D(e,e'p)$ scattering

abstract:
  We present a systematic study of the final-state interaction (FSI) effects in
$D(e,e'p)$ scattering in the CEBAF energy range with particular emphasis on the
phenomenon of the angular anisotropy of the missing momentum distribution. We
find that FSI effects dominate at missing momentum $p_m \gsim 1.5 $fm$^{-1}$.
FSI effects in the excitation of the $S$-wave state are much stronger than in
the excitation of the $D$-wave.


title: Two-Nucleon Solitary Wave Exchange Potentials(SWEPs)

abstract:
  A sine-Gordon solitary wave exchange NN potentials (SG SWEP) is presented as
an example of a large class of realistic potentials with four or less
parameters. SWEPs are derived from nonlinear quantum field theory developed by
Burt. SG SWEPs resemble Reid SC potentials and they reproduce high quality
phase shifts and deuteron parameters with only two parameters.


title: Nuclear Wobbling Motion and Electromagnetic Transitions

abstract:
  The nuclear wobbling motion is studied from a microscopic viewpoint. It is
shown that the expressions not only of the excitation energy but also of the
electromagnetic transition rate in the microscopic RPA framework can be cast
into the corresponding forms of the macroscopic rotor model. Criteria to
identify the rotational band associated with the wobbling motion are given,
based on which examples of realistic calculations are investigated and some
theoretical predictions are presented.


title:
Nucleon-Nucleon Correlations and Six-Quark Cluster Effects in
  Semi-Inclusive Deep Inelastic Lepton Scattering off Few-Nucleon Systems

abstract:
  Semi-inclusive deep inelastic lepton scattering off few-nucleon systems is
investigated assuming that virtual boson absorption occurs on a hadronic
cluster which can be either a two-nucleon correlated pair or a six-quark bag.
In both cases the relevance of nuclear effects on forward and backward nucleon
emissions is illustrated and the differences expected in the energy
distribution of the emitted nucleons are analyzed both at x>1 and x<1.


title: Efimov States in Halo Nuclei

abstract:
  We investigate conditions for the occurrence of Efimov states in the recently
discovered halo nuclei. These states could appear in systems, where one neutron
is added to a pronounced one-neutron halo nucleus. Detailed calculations of the
properties of the states are presented and promising candidates are discussed.


title: Three-Body Halos. II. from Two- to Three-Body Asymptotics

abstract:
  The large distance behavior of weakly bound three-body systems is
investigated. The Schr\"{o}dinger equation and the Faddeev equations are
reformulated by an expansion in eigenfunctions of the angular part of a
corresponding operator. The resulting coupled set of effective radial equations
are then derived. Both two- and three-body asymptotic behavior are possible and
their relative importance is studied for systems where subsystems may be bound.
The system of two nucleons outside a core is studied numerically in detail and
the character of possible halo structure is pointed out and investigated.


title: The Onset of Chaos with a Quadrupole--Quadrupole Interaction

abstract:
  The transition from order to chaos in atomic nuclei has been studied
analytically and numerically using a quadrupole--quadrupole residual
interaction. This interaction leads to chaotic behaviour, but the critical
energy $E_C\simeq 12.6$ MeV, corresponding to the onset of chaos, is higher
than that of the experimental one.


title:
Binding energies and nonradiative decay rates of $H\! ed\mu $-molecular
  ions

abstract:
  The method of hyperspherical "surface" functions has been applied to the
calculation of eigenvalues and eigenfunctions of muonic molecular ions
$^{3,4}\! H\! ed\mu $. Binding energies and nonradiative decay rates for the
states of the total angular momentum $L=0,~1,~2$ have been obtained.


title:
Nucleon-Nucleon and Pion-Nucleon Potentials from Phase Shifts using
  Quantum Inversion

abstract:
  NN and Pi-N partial wave radial potentials have been generated using the
latest SM94-VPI(NN) and FA93-VPI(Pi-N) phase shifts. The potentials are used to
determine the deuteron properties and to compute the 3H and 3He binding
energies. The e_1 mixing angles of SM94-VPI and NY93-Nijmegen differ
significantly and inversion potentials yield a P_d of 6.37% and 5.78%,
respectively. Underbinding of 3H and 3He is enhanced by SM94, which signals
more nonlocality and/or three-body potential effects than predicted from
Nijmegen phase shifts and boson exchange models. The local pion-nucleon S_31,
P_31 and P_33 channel potentials have been generated for guidance and to obtain
a quantitative impression in r-space of what the Pi-N FA93-VPI phase shifts
imply.


title: Quantal Bifurcations in Rotational Spectra of Some Odd Atomic Nuclei

abstract:
  To show the existence of precursor phenomena of the transition order$\
to$chaos in atomic nuclei a simple analysis has been made, based on a recent
criterion proposed by Pavli\-chenkov. The basic idea is that nonlinear effects
in rotational bands should lead to bifurcation, which qualitatively changes the
spectrum for one of the nuclear excitation branches. Experimental data
concerning the isotopes of Er, Hf, Yb, Os, Dy, W strongly support the above
criterion.


title: Periodic Orbits and Shell Structure in Octupole Deformed Potentials

abstract:
  The effect of an octupole term in a quadrupole deformed single particle
potential is studied from the classical and quantum mechanical view point.
Whereas the problem is nonintegrable, the quantum mechanical spectrum
nevertheless shows some shell structure in the superdeformed prolate case for
particular, yet fairly large octupole strengths; for spherical or oblate
deformation the shell structure disappears. This result is associated with
classical periodic orbits which are found by employing the removal of
resonances method; this approximation method allows determination of the shape
of the orbit and of the approximate octupole coupling strength for which it
occurs. The validity of the method is confirmed by solving numerically the
classical equations of motion. The quantum mechanical shell structure is
analysed using the particle number dependence of the fluctuating part of the
total energy. In accordance with the classical result this dependence turns out
to be very similar for a superdeformed prolate potential plus octupole term and
a hyperdeformed prolate potential without octupole term. In this way the shell
structure is explained at least for some few hundred levels. The Fourier
transform of the level density further corroborates these findings.

categories: nucl-th chao-dyn chem-ph cond-mat nlin.CD


title:
Shell Structures and Chaos in Deformed Nuclei and Large Metallic
  Clusters

abstract:
  A reflection-asymmetric deformed oscillator potential is analysed from the
classical and quantum mechanical point of view. The connection between
occurrence of shell structures and classical periodic orbits is studied using
the ''removal of resonances method'' in a classical analysis. In this
approximation, the effective single particle potential becomes separable and
the frequencies of the classical trajectories are easily determined. It turns
out that the winding numbers calculated in this way are in good agreement with
the ones found from the corresponding quantum mechanical spectrum using the
particle number dependence of the fluctuating part of the total energy. When
the octupole term is switched on it is found that prolate shapes are stable
against chaos whereas spherical and oblate cases become chaotic. An attempt is
made to explain this difference in the quantum mechanical context by looking at
the distribution of exceptional points which results from the matrix structure
of the respective Hamiltonians. In a similar way we analyse the modified
Nilsson model and discuss its consequences for nuclei and metallic clusters.


title: Nuclear Coherent versus Incoherent Effects in Peripheral RHI Collisions

abstract:
  We derive simple and physically transparent expressions for the contribution
of the strong interaction to one nucleon removal processes in peripheral
relativistic heavy ion collisions. The coherent contribution,i.e, the
excitation of a giant dipole resonance via meson exchange is shown to be
negligible as well as interference between coulomb and nuclear excitation.
Incoherent nucleon knock out contribution is also derived suggesting the nature
of the nuclear interaction in this class of processes. We also justify the
simple formulae used to fit the data of the E814 Collaboration.


title: Two-body Mechanisms in Pion Photoproduction on the Trinucleon

abstract:
  A breakdown of the Impulse Approximation is studied in pion photoproduction
on $^3$He at high momentum transfers. The usual DWIA formalism with Faddeev
wave functions which works well for small momentum transfers deviates from
experimental measurements by up to two orders of magnitude for $Q^2>6 fm^{-2}$.
It is found that the explicit inclusion of two-body mechanisms, where the
photon is absorbed on one nucleon and the pion is emitted from another nucleon
can restore agreement with the data.


title: Few-Body Physics -- Then and Now

abstract:
  A summary of the XIV\underline{th} International Conference on Few-body
Problems In Physics is given, with an emphasis on the important problems solved
recently and the prognosis for the future of the field. Personal remarks and
``homework'' problem assignments are made.


title:
Spin-Isospin Response Functions and the Effects of the $\Delta$-Hole
  Configurations in Finite Nuclei

abstract:
  Effects of the delta-isobar $(\Delta)$ mixing on the spin-isospin response
functions in finite nuclei are studied in the quasi-elastic region. A method to
calculate the response function for a finite system composed of nucleon $(N)$
and $\Delta$ is formulated in a ring approximation. It is designed to treat the
$\Delta$-related Landau-Migdal parameters, $g'_{N\Delta}$ and
$g'_{\Delta\Delta}$, and the nucleon parameter $g'_{NN}$, independently, so
that the universality ansatz, $g'_{NN}=g'_{N\Delta}=g'_{\Delta\Delta}$, is
removed. We calculated the isovector spin-longitudinal and -transverse response
functions, $R_{L}$ and $R_{T}$, with and without the $\Delta$-mixing. Inclusion
of $\Delta$ enhances $R_{L}$ but reduces $R_{T}$ for ordinary interactions.
Dependence of $R_{L,T}$ on $g'_{NN}$ and $g'_{N\Delta}$ is investigated.
Decomposition into the process-decomposed response functions, $R^{[NN]}$,
$R^{[N\Delta]}$ and $R^{[\Delta\Delta]}$, is very elucidative to see the
$\Delta$ effects, which are found to be mainly governed by $R^{[N\Delta]}$ and
sensitive to $g'_{N\Delta}$. The isovector spin-transverse response function
$R^{(e,e')}_{T}$ obtained by $(e,e')$ is calculated by various effective
interactions and compared to each other as well as experimental data.


title:
Fine Structure Discussion of Parity-Nonconserving Neutron Scattering at
  Epithermal Energies

abstract:
  The large magnitude and the sign correlation effect in the parity
non-conserving resonant scattering of epithermal neutrons from $^{232}$Th is
discussed in terms of a non-collective $2p-1h$ local doorway model. General
conclusions are drawn as to the probability of finding large parity violation
effects in other regions of the periodic table.


title: Physics and Signatures of the Quark - Gluon Plasma

abstract:
  This is a critical review of the various observables that have been proposed
to signal the change from dense hadronic matter to a quark-gluon plasma at high
temperature or baryon density. I discuss current models of quark-gluon plasma
formation in relativistic heavy ion collisions and analyze the virtues and
ambiguities of various signatures. [The author especially invites comments by
interested readers concerning possible inaccuracies or omissions before this
review appears in print.]


title: Relativistic Effect on Low-Energy Nucleon-Deuteron Scattering

abstract:
  The relativistic effect on differential cross sections, nucleon-to-nucleon
and nucleon-to-deuteron polarization transfer coefficients, and the spin
correlation function, of nucleon-deuteron elastic scattering is investigated
employing several three-dimensional relativistic three-body equations and
several nucleon-nucleon potentials. The polarization transfer coefficients are
found to be sensitive to the details of the nucleon-nucleon potentials and the
relativistic dynamics employed, and prefer trinucleon models with the correct
triton binding energy. (To appear in Phys. Rev. C)


title: Radiative capture on neutron rich nuclei

abstract:
  The $({\rm n},\gamma)$--cross sections for neutron--rich oxygen isotopes have
been calculated in the direct capture model. The experimental data for
${^{18}{\rm O}}({\rm n},\gamma){^{19}{\rm O}}$ can be reproduced using this
model. Compared to previous work the cross section for ${^{19-21}{\rm O}}({\rm
n},\gamma){^{20-22}{\rm O}}$ are enhanced considerably by factors between four
and 300.


title: Chaos {\sl vs} Thermalization in the Nuclear Shell Model

abstract:
  Generic signatures of quantum chaos found in realistic shell model
calculations are compared with thermal statistical equilibrium. We show the
similarity of the informational entropy of individual eigenfunctions in the
mean field basis to the thermodynamical entropy found from the level density.
Mean occupation numbers of single-particle orbitals agree with the Fermi-Dirac
distribution despite the strong nucleon interaction.


title: Parity Mixed Doublets in A = 36 Nuclei

abstract:
  The $\gamma$-circular polarizations ($P_{\gamma}$) and asymmetries
($A_{\gamma}$) of the parity forbidden M1 + E2 $\gamma$-decays: $^{36}Cl^{\ast}
(J^{\pi} = 2^{-}; T = 1; E_{x} = 1.95 $ MeV) $\rightarrow$ $^{36}Cl (J^{\pi} =
2^{+}; T = 1; g.s.)$ and $^{36}Ar^{\ast} (J^{\pi} = 2^{-}; T = 0; E_{x} = 4.97
$ MeV) $\rightarrow$ $^{36}Ar^{\ast} (J^{\pi} = 2^{+}; T = 0; E_{x} = 1.97 $
MeV) are investigated theoretically. We use the recently proposed
Warburton-Becker-Brown shell-model interaction. For the weak forces we discuss
comparatively different weak interaction models based on different assumptions
for evaluating the weak meson-hadron coupling constants. The results determine
a range of $P_{\gamma}$ values from which we find the most probable values:
$P_{\gamma}$ = $1.1 \cdot 10^{-4}$ for $^{36}Cl$ and $P_{\gamma}$ = $3.5 \cdot
10^{-4}$ for $^{36}Ar$.


title:
Staggering of the Nuclear Charge Radii in a Superfluid Model with Good
  Particle Number

abstract:
  A simple superfluid model with an effective four body interaction of monopole
pairing type is used to explain the staggering of the charge radii in the
isotope chains. The contribution of deformation and of the particle number
projection are analyzed for the Sn isotopes. Good results are obtained for the
staggering parameters and neutron pairing energies.


title: Pedagogical Studies of Relativistic Hamiltonians

abstract:
  Relativistic Hamiltonians are defined as the sum of relativistic one-body
kinetic energies, two- and many-body interactions and their boost corrections.
We review the calculation of the boost correction of the two-body interaction
from commutation relations of the Poincare group and show that its important
terms can be easily understood from classical relativistic mechanics. The boost
corrections for scalar- and vector- meson-exchange interactions, obtained from
relativistic field theory, are shown to be in agreement with the results of the
classical calculation. These boost corrections are also shown to be necessary
to reproduce the known results of relativistic mean-field theories. We conclude
with comments on the relativistic boost operator for the wave function of a
nucleus. Several of the results presented in this pedagogical article are
known. We hope that a better understanding of relativistic Hamiltonians and
their relation to relativistic field theory is obtained by putting them
together with a few new relations.


title: Theory of fermion to boson mappings: old wine in new bottles

abstract:
  After a brief review of various mappings of fermion pairs to bosons, we
rigorously derive a general approach. Following the methods of Marumori and
Otsuka, Arima, and Iachello, our approach begins with mapping states and
constructs boson representations that preserve fermion matrix elements. In
several cases these representations factor into finite, Hermitian boson images
times a projection or norm operator that embodies the Pauli principle. We pay
particular attention to truncated boson spaces, and describe general methods
for constructing Hermitian and approximately finite boson image Hamiltonians,
including effective operator theory to account for excluded states. This method
is akin to that of Otsuka, Arima, and Iachello introduced in connection with
the Interacting Boson Model, but is more rigorous, general, and systematic.


title:
Variational Monte Carlo Calculations of $^3$H and $^4$He with a
  relativistic Hamiltonian - II

abstract:
  In relativistic Hamiltonians the two-nucleon interaction is expressed as a
sum of $\tilde{v}_{ij}$, the interaction in the ${\bf P}_{ij}=0$ rest frame,
and the ``boost interaction'' $\delta v({\bf P}_{ij})$ which depends upon the
total momentum ${\bf P}_{ij}$ and vanishes in the rest frame. The $\delta v$
can be regarded as a sum of four terms: $\delta v_{RE}$, $\delta v_{LC}$,
$\delta v_{TP}$ and $\delta v_{QM}$; the first three originate from the
relativistic energy-momentum relation, Lorentz contraction and Thomas
precession, while the last is purely quantum. The contributions of $\delta
v_{RE}$ and $\delta v_{LC}$ have been previously calculated with the
variational Monte Carlo method for $^3$H and $^4$He. In this brief note we
report the results of similar calculations for the contributions of $\delta
v_{TP}$ and $\delta v_{QM}$. These are found to be rather small.


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

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


title:
Relativistic models for quasielastic $(e,e')$\ at large momentum
  transfers

abstract:
  Inclusive quasielastic response functions are calculated for electron
scattering in a relativistic model including momentum dependent scalar and
vector mean fields. The momentum dependence of the mean fields is taken from
Dirac optical fits to proton nucleus scattering and is important in describing
data at momentum transfers of 1 GeV/c or larger. Our simple model is applicable
for quasielastic scattering over a large range of momentum transfers.


title:
Spectroscopic Amplitudes for One--Nucleon Transfer Between 1p0f--Shell
  Nuclei

abstract:
  Spectroscopic amplitudes are calculated for one--nucleon transfer between
low--lying, normal--parity states of nuclei in the lower part of the
1p$0\,$f--shell. Calculations are performed using shell--model wave functions
obtained from the diagonalization procedure of a nuclear Hamiltonian in the
space given by the complete set of states generated from the 1p$_{3/2}$,
1p$_{1/2}$, $0\,$f$_{7/2}$ and $0\,$f$_{5/2}$ orbits. The Hamiltonian contains
one and two body interactions derived recently by Richter \etal. Sum rules for
one--nucleon pick--up and stripping reactions are given. The selectivity in
excitation of the final states induced by one--nucleon pick--up or stripping is
discussed.


title: Kaon flow as a probe of the kaon potential in nuclear medium

abstract:
  The flow of kaons, i.e., the average kaon transverse momentum as a function
of rapidity, and the associated flow parameter in heavy-ion collisions at
SIS/GSI energies is investigated in the relativistic transport model. It is
found that the pattern of kaon flow at the final stage is sensitive to the kaon
potential used in the model and is thus a useful probe of the kaon potential in
a nuclear medium.


title: Pion Content of the Nucleon in Polarized Semi-Inclusive D.I.s

abstract:
  An explicit pionic component of the nucleon may be identified by measuring
polarized $\Delta^{++}$ fragments produced in deep-inelastic scattering off
polarized protons. The pion-exchange model predicts highly correlated
polarizations of the $\Delta^{++}$ and target proton, in marked contrast with
the competing diquark fragmentation process.


title:
The Spectral Function for Finite Nuclei in the Local Density
  Approximation

abstract:
  The spectral function for finite nuclei is computed within the framework of
the Local Density Approximation, starting from nuclear matter spectral
functions obtained with a realistic nucleon-nucleon interaction. The spectral
function is decomposed into a single-particle part and a ''correlated'' part;
the latter is treated in the local density approximation.
  As an application momentum distributions, quasi-particle strengths and
overlap functions for valence hole states, and the light-cone momentum
distribution in finite nuclei are computed.


title: q-deformed pairing-vibrations

abstract:
  Boson creation operators constructed from linear combinations of q- deformed
zero coupled nucleon pair operators acting on the nucleus (A,0), are used to
derive pp-RPA equations. The solutions of these equations are the pairing
vibrations in (A${\underline{+}}$2) nuclei. For the $0^+_1$ and $0^+_2$ states
of the nucleus $^{208}$Pb, the variations of relative energies and transfer
cross-sections for populating these states via (t,p) reaction, with deformation
parameter $\tau$ have been analysed. For $\tau=0.405$ the experimental
excitation energy of 4.87MeV and the ratio $\frac{\sigma(0^+_2)
}{\sigma(0^+_1)}=0.45$ are well reproduced. The critical value of pairing
interaction strength for which phase transition takes place, is seen to be
lower for deformed zero-coupled nucleon pair condensate with $\tau$ real,
supporting our earlier conclusion that the real deformation simulates the
two-body residual interaction. For $\tau$ purely imaginary a stronger pairing
interaction is required to bring about the phase transition. The effect of
imaginary deformation is akin to that of an antipairing type repulsive
interaction. Using deformed zero coupled quasi-particle pairs, a deformed
version of Quasi-boson approximation for $0^+$ states in superconducting nuclei
is developed. For the test model of 20 particles in two shells, the results of
q-deformed boson and quasi-boson approximations have been compared with exact
results. It is found that the deformation effectively takes into account the
anharmonicities and may be taken as a quantitative measure of the correlations
not being accounted for in a certain approximate treatment.


title: Chiral Quark Dynamics in Dense Nuclear Matter

abstract:
  We consider a new approach to the description of dense nuclear matter in the
framework of chirally symmetric, quark-based hadron models. As previously in
the Skyrme model, the dense environment is described in terms of hyperspherical
cells of unit baryon number. The intrinsic curvature of these cells generates a
new gauge interaction for the quark fields which mediates interactions with the
ambient matter. We apply this approach to the Nambu-Jona-Lasinio (NJL) model,
construct its curved-space quark propagator and solve the ladder Bethe-Salpeter
equation for the pion. We find a high-density phase transition to chiral
restoration, discuss the density dependence of the chiral order parameter and
of the pion properties, and compare with results of the conventional
chemical-potential approach. The new approach can additionally describe
baryon-density-free cavities in the dense medium.


title:
The apparent Coulomb reacceleration of neutrons in electrodissociation
  of the deuteron

abstract:
  We demonstrate that the final state $p$-$n$ interaction in the reaction of
electrodissociation of the deuteron at large $Q^{2}$ in a static external field
leads to the apparent reacceleration of neutrons. The shift of the neutron
velocity from the velocity of the deuteron beam is related to the
quantum-mechanical forward-backward asymmetry of the missing momentum
distribution in the $^2H(e,e'p)n$ scattering.


title:
Nuclear Charge Density Distributions from Elastic Electron Scattering
  Data

abstract:
  The model independent procedure of extracting charge density distributions
from elastic electron scattering data is investigated. The charge density
distributions are expanded on an orthonormal basis and the parameters of the
expansions are fixed by the comparison with the experimental data. Two bases
with different analytical properties (Fourier-Bessel and Hermite) are used.
This allows us to disentangle the uncertainties coming from the choice of the
expansion basis from those intrinsic to the extraction procedure. We design a
set of tests to select the number of the expansion coefficients adequate for a
proper description of the data. The procedure is applied to elastic data
measured on $^{12}$C, $^{40}$Ca and $^{208}$Pb nuclei.


title:
Nuclear transparencies for nucleons, knocked-out under various
  semi-inclusive conditions

abstract:
  Using hadron dynamics we calculate nuclear transparencies for protons,
knocked-out in high-$Q^2$, semi-inclusive reactions. Predicted transparencies
are, roughly half a standard deviation above the NE18 data. The latter contain
the effects of binned proton missing momenta and mass, and of finite detector
acceptances. In order to test sensitivity we compare computed transparencies
without restrictions and the same with maximal cuts for missing momenta and the
electron energy loss. We find hardly any variation, enabling a meaningful
comparison with data and predictions based on hadron dynamics. Should
discrepancies persist in high-statistics data, the above may with greater
confidence be attributed to exotic components in the description of the
outgoing proton.


title:
Semiclassical expansions up to $\hbar^4$-order in relativistic nuclear
  physics

abstract:
  We present the first calculation of the $\hbar^4$-Wigner--Kirkwood
corrections to a relativistic system of fermions in the presence of external
scalar and vector potentials. The method we propose allows to compute
efficiently semiclassical corrections to one body operators such as mean
energies and local densities. It also preserves gauge invariance and produces
explicitly convergent results despite some apparent divergencies at the
classical turning points. As a byproduct we obtain the $\hbar^4$ corrections
stemming from the polarization of the Dirac sea. We apply our results to the
relativistic $\sigma$-$\omega$ Lagrangian in the Hartree valence approximation.
We compare the semiclassical expansion with the exact result and with the
Strutinsky average whenever it can be obtained. We find that the $\hbar^4 $
corrections are much smaller than typical shell effects. Our results provide
convincing arguments to neglect higher than second order $\hbar$ effects in the
Wigner--Kirkwood scheme to relativistic nuclear physics in the mean field
approximation.


title:
Thermal Equilibration and Expansion in Nucleus-Nucleus Collision at the
  AGS

abstract:
  The rather complete data set of hadron yields from central Si + A collisions
at the Brookhaven AGS is used to test whether the system at freeze-out is in
thermal and hadro-chemical equilibrium. Rapidity and transverse momentum
distributions are discussed with regards to the information they provide on
hydrodynamic flow.


title:
Hexadecapole Interaction and the Delta I=4 Staggering Effect in
  Rotational Bands

abstract:
  A role of the multipole interaction in the description of the $\triangle I$=4
staggering phenomenon is investigated in a model consisting of a single-$j$
shell filled by identical nucleons. Exact diagonalization of the
quadrupole-plus-hexadecapole Hamiltonian shows that the
hexadecapole-hexadecapole interaction can produce a $\triangle I$=4 periodicity
in the yrast sequence.


title:
Collision rates for $\bbox{\rho}$, $\bbox{\omega}$ and $\bbox{\phi}$
  mesons at nonzero temperature

abstract:
  The $\omega$ and $\phi$ mesons are exceptionally narrow in vacua being about
8 and 4 MeV. At finite temperature they will scatter with other hadrons in
their approach to equilibrium and thereafter. These dynamics induce broadening
to the already unstable vector mesons which is calculated in the framework of
relativistic kinetic theory. A rather complete set of low-lying mesons provide
reaction partners whose interactions are modeled using effective Lagrangians.
Collision rates for $\rho$ and $\omega$ are found to be $\sim$ 100 MeV at
$T$=200 MeV while the rate for $\phi$ is $\sim$ 25 MeV. Corresponding mean free
paths are about 1 and 4 fm! Possible observable consequences are discussed.


title:
Application of Multiple Scattering Theory to Lower Energy Elastic
  Nucleon-Nucleus Reactions

abstract:
  The optical model potentials for nucleon-nucleus elastic scattering at
$65$~MeV are calculated for $^{12}$C, $^{16}$O, $^{28}$Si, $^{40}$Ca,
$^{56}$Fe, $^{90}$Zr and $^{208}$Pb in first order multiple scattering theory,
following the prescription of the spectator expansion, where the only inputs
are the free NN potentials, the nuclear densities and the nuclear mean field as
derived from microscopic nuclear structure calculations. These potentials are
used to predict differential cross sections, analyzing powers and spin rotation
functions for neutron and proton scattering at 65 MeV projectile energy and
compared with available experimental data.


title: Total Cross Sections for Neutron Scattering

abstract:
  Measurements of neutron total cross-sections are both extensive and extremely
accurate. Although they place a strong constraint on theoretically constructed
models, there are relatively few comparisons of predictions with experiment.
The total cross-sections for neutron scattering from $^{16}$O and $^{40}$Ca are
calculated as a function of energy from $50-700$~MeV laboratory energy with a
microscopic first order optical potential derived within the framework of the
Watson expansion. Although these results are already in qualitative agreement
with the data, the inclusion of medium corrections to the propagator is
essential to correctly predict the energy dependence given by the experiment.


title:
Variations of Hadron Masses and Matter Properties in Dense Nuclear
  Matter

abstract:
  Using a self-consistent quark model for nuclear matter we investigate
variations of the masses of the non-strange vector mesons, the hyperons and the
nucleon in dense nuclear matter (up to four times the normal nuclear density).
We find that the changes in the hadron masses can be described in terms of the
value of the scalar mean-field in matter. The model is then used to calculate
the density dependence of the quark condensate in-medium, which turns out to be
well approximated by a linear function of the nuclear density. Some relations
among the hadron properties and the in-medium quark condensate are discussed.


title: A theoretical approach to the (pion^{-}, gamma gamma) reaction in nuclei

abstract:
  We have studied the pion^{-} capture in nuclei leading to two photons, using
improved many body methods which have been tested with success in one photon
pion^{-} radiative capture, muon^{-} capture and neutrino scattering. The
qualitative features of the experimental data are reproduced but there are
still some disagreement at small relative photon angles. The reaction is a
potential source of information on details of the gamma-gamma-pion-pion vertex
where chiral corrections can be relevant. New and more precise experiments are
planned which make calculations like the present one relevant and opportune.
---------------------------------------------------------


title: Correlations in a Many-Body Calculation of $^{\bf 11}$Li

abstract:
  A many-body calculation of $^{11}$Li is presented where the only input is the
well-tested, finite-range {\it D1S} effective interaction of {\it Gogny}.
Pairing correlations are included in a constrained Hartree-Fock-Bogolyubov
calculation, while long-range collective correlations are introduced using a
GCM derived calculation. Correlations are found to play an important role in
describing $^{11}$Li. A substantive underlying $^9$Li core of $^{11}$Li is
found, which has a different density profile than a free $^9$Li nucleus. This
may have significant implications in the use of a three-body framework in
studies of $^{11}$Li.


title: Mean Field Studies of Exotic Nuclei}

abstract:
  {Full three dimensional static and dynamic mean field calculations using
collocation basis splines with a Skyrme type Hamiltonian are described. This
program is developed to address the difficult theoretical challenges offered by
exotic nuclei. Ground state and deformation properties are calculated using
static Hartree-Fock, Hartree-Fock+BCS and constrained Hartree-Fock models.
Collective properties, such as reaction rates and resonances, are described
using a new alternate method for evaluating linear response theory, which is
constructed directly on top of the static calculation. This provides a
consistent description of the ground state, deformation and collective nuclear
properties. Sample results are presented for the giant multiple resonances of
$^{16}$O. }


title: Widths of $\Xi$ Hypernuclear States

abstract:
  The $\Lambda$ and neutron decay widths of $\Xi$ hypernuclear states, based on
calculated $\Xi N \to \lala$ mixing amplitudes, are estimated. The widths which
result from using the Nijmegen Model D interaction are sufficiently small, of
order 1.5 MeV, that experiments to observe $\Xi$ hypernuclear states using the
$(K^-,K^+)$ reaction may be feasible.


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

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


title: Quadrupole Collective States in a Large Single-J Shell

abstract:
  We discuss the ability of the generator coordinate method (GCM) to select
collective states in microscopic calculations. The model studied is a
single-$j$ shell with hamiltonian containing the quadrupole-quadrupole
interaction. Quadrupole collective excitations are constructed by means of the
quadrupole single-particle operator. Lowest collective bands for $j$=31/2 and
particle numbers $N$=4,6,8,10,12, and $14$ are found. For lower values of $j$,
exact solutions are obtained and compared with the GCM results.


title:
The Role of Final State Interactions in Quasielastic $^{56}$Fe$(e,e')$
  Reactions at large $|\vec q|$

abstract:
  A relativistic finite nucleus calculation using a Dirac optical potential is
used to investigate the importance of final state interactions [FSI] at large
momentum transfers in inclusive quasielastic electronuclear reactions. The
optical potential is derived from first-order multiple scattering theory and
then is used to calculate the FSI in a nonspectral Green's function doorway
approach. At intermediate momentum transfers excellent predictions of the
quasielastic $^{56}$Fe$(e,e')$ experimental data for the longitudinal response
function are obtained. In comparisons with recent measurements at $|{\vec
q|}=1.14$~GeV/c the theoretical calculations of $R_L$ give good agreement for
the quasielastic peak shape and amplitude, but place the position of the peak
at an energy transfer of about $40$~MeV higher than the data.


title: Measurement of the Reaction $^{12}C(\nu_\mu,\mu^-) X$ Near Threshold

abstract:
  The reaction $^{12}C(\nu_\mu,\mu^-) X$ has been measured near threshold using
a $\pi ^+$ decay-in-flight $\nu_\mu$ beam from the Los Alamos Meson Physics
Facility and a massive liquid scintillator neutrino detector (LSND). In the
energy region $123.7 < E_\nu < 280$ MeV, the measured spectral shape is
consistent with that expected from the Fermi Gas Model. However, the measured
flux-averaged inclusive cross section ($(8.3 \pm 0.7 stat. \pm 1.6 syst.)
\times 10^{-40} cm^2$) is more than a factor of 2 lower than that predicted by
the Fermi Gas Model and by a recent random phase approximation calculation.


title: Delta--Excitation and Exchange Corrections for NN--Bremsstrahlung

abstract:
  The role of the relativistic amplitudes for a number of ${\cal O}(k)$
processes usually neglected in potential model calculations of
NN--bremsstrahlung is investigated. In particular, we consider the
$\Delta$--excitation pole contributions related to the one--pion and one--rho
exchange and in addition include the exchange contributions induced by the
radiative $\omega,\,\rho \to \pi \gamma$ decays. The contributions are
calculated from relativistic Born amplitudes fitted to $\Delta$--production and
absorption data in the energy range up to 1 GeV and then used to supplement
potential model and soft photon calculations for nucleon--nucleon
bremsstrahlung. The effects on $NN\gamma$--observables, although moderate in
general, are found to be important in some kinematic domains.


title: Self weakening of the tensor interaction in a nucleus

abstract:
  We examine several ``landmarks'' for the effects of the tensor interaction on
the properties of light nuclei. These were usually discussed in the context of
small-space shell-model calculations. We show, using $G$ matrices derived from
a realistic nucleon-nucleon potential, that when the model space is small
(e.g., $0\hbar\omega$), these effects are overestimated, indicating that the
tensor interaction is too strong. However, when larger spaces are used, there
is a diminishing of these effects, which, in general, leads to better agreement
with experiment.


title: The Delta I=4 Bifurcation in Superdeformed Bands

abstract:
  The origin of the Delta I=4 staggering effect which has recently been
observed in several superdeformed bands is discussed. The Hamamoto and
Mottelson model, which is based on a phenomenological parametrization of the
hamiltonian as a quartic function of angular momentum, is analyzed. A stability
of the description with respect to the C_4 - symmetry breaking terms is
studied.


title:
Isospin Recoupling and Bose-Einstein Pion Correlations in
  Nucleon-Antinucleon Annihilations

abstract:
  We study the effect of isospin projections on a two source picture of
coherent pions coming from nucleon-antinucleon annihilation. We show that
important Hanbury-Brown Twiss correlations among like charge pion pairs
compared with unlike arise from these isospin projections.


title:
Impact-Parameter Dependence of Multiple Lepton-pair Production from
  Electromagnetic Fields

abstract:
  In relativistic heavy-ion collisions, the strong Lorentz-contracted
electromagnetic fields are capable of producing copious numbers of lepton pairs
through the two-photon mechanism. Monte Carlo techniques have been developed
that allow the exact calculation of production by this mechanism when a
semi-classical approximation is made to the motion of the two ions. Here, we
develop a hybrid Monte Carlo technique that enables us to calculate the impact
parameter dependence of the two-photon mechanism for lepton-pair production,
and by using this result, we obtain the probability distribution for
multiple-pair production as a function of impact parameter. Computations are
performed for S$+$Au and Pb$+$Pb systems at 200 A GeV and 160 A GeV,
respectively. We also compare our results with the equivalent photon
approximation and elucidate the differences.


title: Charge Exchange Processes between Excited Helium and Fully Stripped Ions

abstract:
  We made a classical trajectory Monte Carlo (CTMC) calculation of state
selective cross sections for processes between some light ions and excited
helium. The results, useful for analysis of spectroscopic data of fusion
devices, are in good agreement with theoretical predictions of scaling laws.


title: Octupole Correlations in Excited Bands of Superdeformed Dy-152

abstract:
  RPA calculations, based on the cranked shell model, are performed for
superdeformed \dy\ in which five excited bands have been found recently. We
show that characteristic features of the observed dynamical moments of inertia
are well accounted for by explicitly taking the octupole correlations into
account. Importance of the interplay between rotation and octupole vibrations
is stressed, and it is suggested that one of the observed excited bands might
be a collective octupole vibration built on the superdeformed yrast band.


title: Time Reversal Symmetry Breaking Effects in Resonant Nuclear Reactions

abstract:
  We incorporate time reversal symmetry breaking (TRSB) effects into the theory
of compound nuclear reactions. We show that the only meaningful test of TRSB in
the overlapping resonances regime is through the study of cross-section
correlations. The effect is channel-dependent. In the isolated resonance
regime, we employ $K$-matrix theory to show the impact of TRSB using the fact
that when only one eigen-channel participates in populating and depopulating
the compound resonance.


title: Auxiliary potential in no-core shell-model calculations

abstract:
  The Lee-Suzuki iteration method is used to include the folded diagrams in the
calculation of the two-body effective interaction $v^{(2)}_{\rm eff}$ between
two nucleons in a no-core model space. This effective interaction still depends
upon the choice of single-particle basis utilized in the shell-model
calculation. Using a harmonic-oscillator single-particle basis and the
Reid-soft-core {\it NN} potential, we find that $v^{(2)}_{\rm eff}$ overbinds
$^4\mbox{He}$ in 0, 2, and $4\hbar\Omega$ model spaces. As the size of the
model space increases, the amount of overbinding decreases significantly. This
problem of overbinding in small model spaces is due to neglecting effective
three- and four-body forces. Contributions of effective many-body forces are
suppressed by using the Brueckner-Hartree-Fock single-particle Hamiltonian.


title: Where the Nuclear Pions are

abstract:
  Three recent experiments, which looked at pionic effects in nuclei have
concluded that there are no excess pions. This puts into serious question the
conventional meson-exchange picture of the nucleon-nucleon interaction. Based
on arguments of partial restoration of chiral symmetry with density we propose
a resolution to this problem.


title: Time Reversal Invariance in the beta-Decays of A = 8 Nuclei

abstract:
  We examine time reversal invariance in the beta-decays of 8B(2+) and 8Li(2+)
to 8Be(2+) in detail, with particular attention to final state interactions of
the two alpha particles from the decay of 8Be, and of the electron (positron)
with the daughter nucleus. A R-matrix formulation is used, with the initial
state described by a shell model. The R-matrix parameters are obtained by
fitting the alpha-\alpha scattering phase shifts and allowed beta-decay rates.
Because the nuclear final state interaction effects on the time reversal test
come from second forbidden beta-decays, they are small and can be minimized by
a suitable choice of kinematic conditions. The e(+/-)-nucleus Coulomb
interaction induced T-violation effects depend on the first forbidden
operators.


title: Comparison of potential models with the np scattering data below 350 MeV

abstract:
  As a follow-up on our earlier paper we calculate the $\chi^{2}$ of various
$N\!N$ potential models with respect to the $np$ scattering data. We find that
only the most recent potential models give a reasonably good description of
these data. Almost none of the potentials is truly an $N\!N$ potential in the
sense that it gives a good description of both $pp$ and $np$ scattering
simultaneously.


title: Closed shells at drip-line nuclei

abstract:
  The shell structure of magic nuclei far from stability is discussed in terms
of the self-consistent spherical Hartree-Fock-Bogoliubov theory. In particular,
the sensitivity of the shell-gap sizes and the two-neutron separation energies
to the choice of particle-hole and particle-particle components of the
effective interaction is investigated.


title: Color Transparency Assumptions

abstract:
  An exactly solvable model is used to investigate the assumptions behind color
transparency.


title:
Momentum and Energy Distributions of Nucleons in Finite Nuclei due to
  Short-Range Correlations

abstract:
  The influence of short-range correlations on the momentum and energy
distribution of nucleons in nuclei is evaluated assuming a realistic
meson-exchange potential for the nucleon-nucleon interaction. Using the
Green-function approach the calculations are performed directly for the finite
nucleus $^{16}$O avoiding the local density approximation and its reference to
studies of infinite nuclear matter. The nucleon-nucleon correlations induced by
the short-range and tensor components of the interaction yield an enhancement
of the momentum distribution at high momenta as compared to the Hartree-Fock
description. These high-momentum components should be observed mainly in
nucleon knockout reactions like $(e,e'p)$ leaving the final nucleus in a state
of high excitation energy. Our analysis also demonstrates that non-negligible
contributions to the momentum distribution should be found in partial waves
which are unoccupied in the simple shell-model. The treatment of correlations
beyond the Brueckner-Hartree-Fock approximation also yields an improvement for
the calculated ground-state properties.


title:
Investigation of the Neutron Form Factors by Inclusive Quasi-Elastic
  Scattering of Polarized Electrons off Polarized $^{3}$He: A Theoretical
  Overview

abstract:
  The theory of quasi-elastic inclusive scattering of polarized leptons off
polarized $^3$He is critically reviewed and the origin of different expressions
for the polarized nuclear response function appearing in the literature is
explained. The sensitivity of the longitudinal asymmetry upon the neutron form
factors is thoroughly investigated and the role played by the polarization
angle for minimizing the proton contribution is illustrated.


title: Probing Deformed Orbitals with \vec{A}(\vec{e}, e' N)B reactions

abstract:
  We present results for response functions and asymmetries in the nuclear
reactions 37\vec{Ar}(\vec{e},e'n)36Ar and 37\vec{K}(\vec{e},e' p)36Ar at
quasifree kinematics. We compare PWIA results obtained using deformed HF wave
functions with PWIA and DWIA results obtained assuming a spherical mean field.
We show that the complex structure of the deformed orbitals can be probed by
coincidence measurements with polarized beam and targets.


title: Spin dependent Momentum Distributions in Deformed Nuclei

abstract:
  We study the properties of the spin dependent one body density in momentum
space for odd--A polarized deformed nuclei within the mean field approximation.
We derive analytic expressions connecting intrinsic and laboratory momentum
distributions. The latter are related to observable transition densities in
{\bf p}--space that can be probed in one nucleon knock--out reactions from
polarized targets. It is shown that most of the information contained in the
intrinsic spin dependent momentum distribution is lost when the nucleus is not
polarized. Results are presented and discussed for two prolate nuclei,
$^{21}$Ne and $^{25}$Mg, and for one oblate nucleus, $^{37}$Ar. The effects of
deformation are highlighted by comparison to the case of odd--A nuclei in the
spherical model.


title:
A quark-cluster description of the EMC effect (Seminar given in the 18th
  Course of the "International School on Nuclear Physics", 16-23/9/'94, Erice,
  IT. To be published in Progress in Particle and Nuclear Physics, Vol. 34,
  Pergamon Press)

abstract:
  The response of a nucleus composed of nucleons and confined quarks is
calculated in a non-relativistic cluster model and is shown to be a convolution
of responses of, respectively, a nucleus with interacting point-nucleons and of
a nucleon composed of quarks. We further show that the apparent off-shell
energy in the expression for the nucleon structure function in Impulse
Approximation does not constitue a real problem. We conjecture a generalization
to the relativistic regime.


title: A stopped Delta-Matter Source in Heavy Ion Collisions at 10 GeV/n

abstract:
  We predict the formation of highly dense baryon-rich resonance matter in
Au+Au collisions at AGS energies. The final pion yields show observable signs
for resonance matter. The Delta(1232) resonance is predicted to be the dominant
source for pions of small transverse momenta. Rescattering effects --
consecutive excitation and deexcitation of Deltas -- lead to a long apparent
lifetime (> 10 fm/c) and rather large volumina (several 100 fm^3) of the
Delta-matter state. Heavier baryon resonances prove to be crucial for reaction
dynamics and particle production at AGS.


title: Double beta decay of $^{100}Mo$: the deformed limit

abstract:
  The double beta decay of $^{100}Mo$ to the ground state and excited states of
$^{100}Ru$ is analysed in the context of the pseudo SU(3) scheme. The results
of this deformed limit are compared with the vibrational one based on the QRPA
formalism. Consistency between the deformed limit and the experimental
information is found for various $\beta\beta$ transitions, although, in this
approximation some energies and B(E2) intensities cannot reproduced.


title: Nuclear Multifragmentation Critical Exponents

abstract:
  We show that the critical exponents of nuclear multi-fragmentation have not
been determined conclusively yet.


title: Generalized Pseudo-SU(3) Model and Pairing

abstract:
  The pseudo-SU(3) model is extended to explicitly include the spin and
proton-neutron degrees of freedom. A general formalism for evaluating matrix
elements of one-body and two-body tensor operators within this framework is
presented. The pairing interaction, which couples different irreducible
representations of SU(3), is expressed in terms of pseudo-space tensors and a
general result is given for calculating its matrix elements. The importance of
pairing correlations in pseudo-SU(3) model calculations is demonstrated by
examining the dependence of wavefunctions, low-energy collective excitation
spectra, and moments of inertia on the strength of the pairing interaction.


title:
Combined Description of $\bf{\overline{N}N}$ Scattering and Annihilation
  With A Hadronic Model

abstract:
  A model for the nucleon-antinucleon interaction is presented which is based
on meson-baryon dynamics. The elastic part is the $G$-parity transform of the
Bonn $NN$ potential. Annihilation into two mesons is described in terms of
microscopic baryon-exchange processes including all possible combinations of
$\pi,\eta,\rho,\omega,a_0,f_0,a_1,f_1,a_2,f_2,K,K^*$. The remaining
annihilation part is taken into account by a phenomenological energy- and state
independent optical potential of Gaussian form. The model enables a
simultaneous description of nucleon-antinucleon scattering and annihilation
phenomena with fair quality.


title:
Limits on the neutron-antineutron oscillation time from the stability of
  nuclei

abstract:
  We refute a recent claim by Nazaruk that the limits placed on the free--space
neutron--antineutron oscillation time $\tau_{{n\bar n}}$ can be improved by
many orders of magnitude with respect to the estimate $\tau_{{n\bar
n}}>2(T_0/\Gamma)^{1/2}$, where $T_0$ is a measured limit on the annihilation
lifetime of a nucleus and $\Gamma\sim 100$ MeV is a typical antineutron-nucleus
annihilation width.


title: Baryon Current Matrix Elements in a Light-Front Framework

abstract:
  Current matrix elements and observables for electro- and photo-excitation of
baryons from the nucleon are studied in a light-front framework. Relativistic
effects are estimated by comparison to a nonrelativistic model, where we use
simple basis states to represent the baryon wavefunctions. Sizeable
relativistic effects are found for certain transitions, for example, to radial
excitations such as that conventionally used to describe to the Roper
resonance. A systematic study shows that the violation of rotational covariance
of the baryon transition matrix elements stemming from the use of one-body
currents is generally small.


title: On an Extended PCAC Relationship

abstract:
  We explore a consistent way to extend the partially conserved axial vector
current (PCAC) relationship and corresponding current algebra results in two
strongly correlated directions: 1) towards a search for a set of systematic
rules for the establishment of PCAC related relationships in a finite low
momentum transfer region and for the extrapolation of the momentum transfer
$q^2$ to zero when deriving the low energy PCAC results that can be compared to
experimental data and 2) towards taking into account, besides the conventional
one, the only other possibility of the spontaneous chiral symmetry breaking,
$SU(2)_L\times SU(2)_R \to SU(2)_V$, inside a baryonic system by a condensation
(in the sense to be specified in the paper) of diquarks. The paper includes
investigations of a chiral Ward--Takahashi identity, the explicit chiral
symmetry breaking by a finite current quark mass, the modification of the PCAC
relationship and its consequences. It is shown that the signals for a
hypothetical diquark condensation inside a nucleon and nucleus is observable in
high precision experiments despite the fact that they may evade most of the
current observations. We briefly discuss how diquark condensation could provide
an answer to the question of where about of pions and quark number in a nucleon
and a nucleus, which is raised in explaining puzzles in polarized pion nucleus
scattering, violation of Gottfried sum rule and EMC effects.


title: Nuclear Breathing Mode in the Relativistic Mean Field Theory

abstract:
  The breathing-mode giant monopole resonance is studied within the framework
of the relativistic mean-field (RMF) theory. Using a broad range of parameter
sets, an analysis of constrained incompressibility and excitation energy of
isoscalar monopole states in finite nuclei is performed. It is shown that the
non-linear scalar self-interaction and the resulting surface properties
influence the breathing-mode considerably. It is observed that dynamical
surface properties respond differently in the RMF theory than in the Skyrme
approach. A comparison is made with the incompressibility derived from the
semi-infinite nuclear matter and with constrained nonrelativistic Skyrme
Hartree-Fock calculaions.


title: Double Delta Production in the gamma d ---> p n pi+ pi- Reaction

abstract:
  We have studied the gamma d ---> Delta++ Delta- reaction which requires the
collaboration of the two nucleons in deuteron. By means of a model previously
developed for the gamma p ----> p pi+ pi- reaction, the two body exchange
currents leading to double delta creation are derived. A fair agreement is
obtained with a recent experiment, but more precise measurements and the
extension to higher photon energies look advisable in order to see the limits
of the present theoretical approach


title: Enhancement of low-${m_t}$ kaons in AGS heavy-ion collisions

abstract:
  In the relativistic transport model, we show that the recently observed
enhancement of low-$m_t$ kaons ($K^+$ and $K^-$) in Si+Pb collisions at AGS can
be explained if a density isomer is introduced in the nuclear
equation-of-state.


title: On the structure of the scalar mesons $f_0(975)$ and $a_0(980)$

abstract:
  We investigate the structure of the scalar mesons $f_0(975)$ and $a_0(980)$
within realistic meson-exchange models of the $\pi\pi$ and $\pi\eta$
interactions. Starting from a modified version of the J\"ulich model for
$\pi\pi$ scattering we perform an analysis of the pole structure of the
resulting scattering amplitude and find, in contrast to existing models, a
somewhat large mass for the $f_0(975)$ ($m_{f_0}=1015$ MeV, $\Gamma_{f_0}=30$
MeV). It is shown that our model provides a description of
$J/\psi\rightarrow\phi\pi\pi/\phi KK$ data comparable in quality with those of
alternative models. Furthermore, the formalism developed for the $\pi\pi$
system is consistently extended to the $\pi\eta$ interaction leading to a
description of the $a_0(980)$ as a dynamically generated threshold effect
(which is therefore neither a conventional $q\overline{q}$ state nor a
$K\overline{K}$ bound state). Exploring the corresponding pole position the
$a_0(980)$ is found to be rather broad ($m_{a_0}=991$ MeV, $\Gamma_{a_0}=202$
MeV). The experimentally observed smaller width results from the influence of
the nearby $K\overline{K}$ threshold on this pole.


title:
A dynamical model for correlated two-pion-exchange in the pion-nucleon
  interaction

abstract:
  A microscopic model for the $N\bar N\to\pi\pi$ process is presented in the
meson exchange framework, which in the pseudophysical region agrees with
available quasiempirical information. The scalar ($\sigma$) and vector ($\rho$)
piece of correlated two--pion exchange in the pion--nucleon interaction is then
derived via dispersion integrals over the unitarity cut. Inherent ambiguities
in the method and implications for the description of pion--nucleon scattering
data are discussed.


title: Charge Radii of Hyperons

abstract:
  The momentum projected SU(3) Chiral Color Dielectric Model (CCDM) is employed
to calculate the charge root mean square radii and charge distributions of
hyperons. We compare our result with Skyrme, MIT bag and Cloudy Bag model
results. The charge distribution of $\Lambda$ in CCDM is similar to that of
Skyrme Model prediction.


title: Subthreshold kaon production and the nuclear equation of state

abstract:
  We reexamine in the relativistic transport model the dependence of kaon yield
on the nuclear equation of state in heavy ion collisions at energies that are
below the threshold for kaon production from the nucleon-nucleon interaction in
free space. For Au+Au collisions at 1 GeV/nucleon, we find that the kaon yield
measured by the Kaos collaboration at GSI can be accounted for if a soft
nuclear equation of state is used. We also confirm the results obtained in the
non-relativistic transport model that the dependence of kaon yield on the
nuclear equation of state is more appreciable in heavy ion collisions at lower
incident energies. We further clarify the difference between the predictions
from the relativistic transport model and the non-relativistic transport model
with a momentum-dependent potential.


title: Pion and Eta Photoproduction in Nuclei

abstract:
  We calculate the quasifree photoproduction of pions and eta mesons on nuclei
from 12C to 208Pb. Assuming that for the quasifree process the cross sections
for pi/eta - photoproduction on a nucleon in medium are -- besides a lowering
due to Pauli blocking -- identical to those on a free nucleon, we use these as
an input. The produced mesons or resonances then propagate through the nucleus
where they can undergo several scattering and absorption processes. This final
state interaction, which leads to a lowering of the initial meson yield up to
70%, we simulate in a coupled channel Boltzmann-Uehling-Uhlenbeck transport
model. It allows us to study in detail the influence of Fermi motion, Pauli
blocking and of the additional decay channels for nucleon resonances in medium
on the photoproduction cross section. The calculated total and differential
cross sections are compared to experimental data and the influence of the
different medium effects on the cross sections is discussed in detail.


title: Hadron-Hadron Interactions

abstract:
  The present status of the chiral approach to the $NN$ interaction as proposed
by Weinberg is discussed. The important role of correlation effects and
explicit vector meson ($\rho$, $\omega$) exchange in the dynamics of
baryon-baryon interactions is demonstrated. As an example, the inclusion of the
exchange of a correlated pair of $\pi$ and $\rho$ meson between two nucleons
appears to be mandatory in order to resolve a long-standing puzzle concerning
the formfactor at the pion-nucleon-nucleon vertex.


title: Importance of Baryon-Baryon Coupling in Hypernuclei

abstract:
  The $\Lambda N - \Sigma N$ coupling in $\Lambda$--hypernuclei and $\Lambda
\Lambda - \Xi N$ coupling in $\Lambda \Lambda$--hypernuclei produce novel
physics not observed in the conventional, nonstrange sector. Effects of
$\Lambda \leftrightarrow \Sigma$ conversion in $^3_{\Lambda}$H are reviewed.
The role of $\Lambda N - \Sigma N$ coupling suppression in the $A=4,5$
$\Lambda$--hypernuclei due to Pauli blocking is highlighted, and the
implications for the structure of $^{10}_{\;\, \Lambda}$B are explored.
Suppression of $\Lambda \Lambda - \Xi N$ conversion in $^{\;\;\, 6}_{\Lambda
\Lambda}$He is hypothesized as the reason that the $< V_{\Lambda \Lambda} >$
matrix element is small. Measurement of $^{\;\;\, 4}_{\Lambda \Lambda}$H is
proposed to investigate the full $\Lambda \Lambda - \Xi N$ interaction. The
implication for $\Lambda \Lambda$ analog states is discussed.


title: An explanatory study of $^{11}$Li $\beta$ decay into $^9$Li and deuteron

abstract:
  The $\beta$-decay of $^{11}$Li into $^9$Li and {\it d} is studied using
simple halo wave functions of $^{11}$Li.
  The sensitivity of the transition probability is elucidated on a description
of the halo part and on a choice of the potential between $^9$Li and {\it d} .


title: Double Pion Photoproduction in Nuclei

abstract:
  The inclusive A(gamma,pi+ pi-)X reaction is studied theoretically. A sizeable
enhancement of the cross section is found, in comparison with the scaling of
the deuteron cross section (sigma_deuteron * A/2). This enhancement is due to
the modifications in the nuclear medium of the gamma N ----> pi pi N amplitude
and the pion dispersion relation. The enhancement is found to be bigger than
the one already observed in the (pi,pi pi) reaction in nuclei.


title:
The Effective Non-Relativistic Hamiltonian for Electron-Nucleus
  Interaction

abstract:
  We present the effective Hamiltonian for an electron-nucleus interaction in
non-relativistic limit up to the second order in the inverse nucleon mass. This
Hamiltonian takes into account the distortion of electron waves and allows to
calculate its effect as well as matrix elements for off-shell transitions in
$(e,e'p)$ reactions.


title: On the Off-Mass-Shell Deformation of the Nucleon Structure Function

abstract:
  The off-mass-shell behavior of the nucleon structure function, $F_2^N$, is
studied within an approach motivated by the Sullivan model. Deep inelastic
scattering on the nucleon is considered in the second order in the pion-nucleon
coupling constant, corresponding to the dressing of the bare nucleons by the
mesonic cloud. The inclusive and semi-inclusive deep inelastic processes on the
deuteron involving off-shell nucleons are considered. A deformation of the
mesonic cloud for the off-mass-shell nucleon, compared to the free one,
generates observable effects in deep inelastic scattering. In particular, it
leads to the breakdown of the convolution model, i.e. the deuteron structure
functions are not expressed through the free nucleon structure function.
Analysis of the semi-inclusive deep inelastic scattering on the deuteron, in
the spectator approximation, shows that this reaction opens new possibilities
to study the role of the off-shell effects in determining in detail the nucleon
structure function.


title: Temperatures of Fragment Kinetic Energy Spectra

abstract:
  Multifragmentation reactions without large compression in the initial state
(proton-induced reactions, reverse-kinematics, projectile fragmentation) are
examined, and it is verified quantitatively that the high temperatures obtained
from fragment kinetic energy spectra and lower temperatures obtained from
observables such as level population or isotope ratios can be understood in a
common framework.


title:
String Models for Ultrarelativistic Hadronic Interactions: Concepts,
  Limitations, and New Directions

abstract:
  After a brief description of the basic theoretical concepts of the string
model approach, we discuss the limitations of the method, at low energies, at
high energies, and at high particle densities. We also report on recent efforts
to overcome these limitations.


title: The Drell-Hearn-Gerasimov Sum Rule

abstract:
  The Drell-Hearn-Gerasimov (DHG) sum rule relates the helicity structure of
the photoabsorption cross section to the anomalous magnetic moment of the
nucleon. It is based on Lorentz and gauge invariance, crossing symmetry,
causality and unitarity. A generalized DHG sum rule my be derived for virtual
photons. At low momentum transfer this generalized sum rule is saturated by the
resonance region, at high momentum transfer it may be expressed by the parton
spin distributions measured in deep inelastic scattering. The
longitudinal-transverse interference determines the Cottingham sum rule, which
is related to the electric and magnetic form factors over the whole range of
momentum transfer.


title:
Slow proton production in semi-inclusive deep inelastic scattering and
  the pion cloud in the nucleon

abstract:
  The semi-inclusive cross section for producing slow protons in charged
current deep inelastic (anti-) neutrino scattering on protons and neutrons is
calculated as a function of the Bjorken $x$ and the proton momentum. The
standard hadronization models based upon the colour neutralization mechanism
appear to underestimate the rate of slow proton production on hydrogen. The
presence of the virtual mesons (pions) in the nucleon leads to an additional
mechanism for proton production, referred to as spectator process. It is found
that at low proton momenta both mechanisms compete, whereas the spectator
mechanism dominates at very small momenta, while the color neutralization
mechanism dominates at momenta larger than 1-2 \, GeV$/c$. The results of the
calculations are compared with the CERN bubble chamber (BEBC) data. The
spectator model predicts a sharp increase of the semi-inclusive cross section
at small $x$ due to the sea quarks in virtual mesons.


title:
Low-energy theorem for a composite particle in mean scalar and vector
  fields

abstract:
  For a relativistic particle moving in the presence of mean scalar and vector
fields, the energy at second order in the scalar field is shown to contain two
contributions in general. One is a momentum-dependent repulsive interaction
satisfying a low-energy theorem pointed out by Wallace, Gross and Tjon. The
other does not vanish at zero-momentum and involves a ``polarisability" of the
particle by the scalar field. The first of these contributions is independent
of the details of the structure of the particle and the couplings of its
constituents to the external fields. The appearance of such a piece in the
central nucleon-nucleus potential thus would support the existence of strong
scalar fields in nuclei, without requiring the use of a Dirac equation for the
nucleon.


title: Effective Group Structure in the Interacting Boson Model

abstract:
  Spectrum generating algebras are used in various fields of physics as models
to determine quantum structure, including energy levels and transition
strengths. The advantage of such models is that their group structure allows an
extensive understanding of the system being studied. In addition they possess a
simple classical limit, at least for bosonic systems. In this paper we discuss
an algebraic model of nuclear structure, the Interacting Boson Model (IBM), and
show that in one limit its group structure is particularly simple. For zero
angular momentum there is an effective lower dimensional group structure which
describes the system both classically and quantum mechanically.


title:
Nonlinear extension of the u(2) algebra as the symmetry algebra of the
  planar anisotropic quantum harmonic oscillator with rational ratio of
  frequencies and ``pancake'' nuclei

abstract:
  The symmetry algebra of the two-dimensional anisotropic quantum harmonic
oscillator with rational ratio of frequencies, which is characterizing
``pancake'' nuclei, is identified as a non-linear extension of the u(2)
algebra. The finite dimensional representation modules of this algebra are
studied and the energy eigenvalues are determined using algebraic methods of
general applicability to quantum superintegrable systems. For labelling the
degenerate states an ``angular momentum'' operator is introduced, the
eigenvalues of which are roots of appropriate generalized Hermite polynomials.
In the special case with frequency ratio 2:1 the resulting algebra is
identified as the finite W algebra W$_3^{(2)}$.


title:
The energy dependence of the $\pi N$ amplitude and the three-nucleon
  interaction

abstract:
  By calculating the contribution of the $\pi-\pi$ three-body force to the
three-nucleon binding energy in terms of the $\pi N$ amplitude using
perturbation theory, we are able to determine the importance of the energy
dependence and the contribution of the different partial waves of the $\pi N$
amplitude to the three-nucleon force. A separable representation of the
non-pole $\pi N$ amplitude allows us to write the three-nucleon force in terms
of the amplitude for $NN\rightarrow NN^*$, propagation of the $NNN^*$ system,
and the amplitude for $NN^*\rightarrow NN$, with $N^*$ being the $\pi N$
quasi-particle amplitude in a given state. The division of the $\pi N$
amplitude into a pole and non-pole gives a procedure for the determination of
the $\pi NN$ form factor within the model. The total contribution of the
three-body force to the binding energy of the triton for the separable
approximation to the Paris nucleon-nucleon potential (PEST) is found to be very
small mainly as a result of the energy dependence of the $\pi N$ amplitude, the
cancellation between the $S$- and $P$-wave $\pi N$ amplitudes, and the soft
$\pi NN$ form factor.


title: Deformed Hartree-Fock Calculation of Proton-Rich Nuclei

abstract:
  We perform Hartree-Fock+BCS calculations for even-even nuclei with 2 <= Z <=
82 and N ranging from outside the proton drip line to the experimental frontier
on the neutron-rich side. The ground state solutions are obtained for 737
nuclei, together with shape-coexistence solutions for 480 nuclei. Our method
features the Cartesian-mesh representation of single-particle wavefunctions,
which is advantageous in treating nucleon skins and exotic shapes. The results
are compared with those of the finite-range droplet model of Moller et al. as
well as the experimental values.


title: The String Model for Ultrarelativistic Nuclear Scattering

abstract:
  We review basic theoretical concepts to describe nuclear collisions at
ultrarelativistic energies. We discuss relativistic strings, Gribov--Regge
theory (GRT) of hadronic interactions and string models based on GRT, and
finally generalizations to nucleus--nucleus scattering.
  - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Invited Lecture at the `` International School--Workshop on Relativistic Heavy
Ion Physics'', Prague, Czech Republic, Sept. 19-23, 1994


title:
Role of Meson-Meson Correlation Effects in the $\NNb\to\rho\pi$
  Annihilation Process

abstract:
  Meson-meson correlation effects are investigated in the $\NNb\to\rho\pi$
annihilation process using a realistic meson-exchange model for the $\rho\pi$
interaction determined previously, together with a conventional baryon-exchange
transition model and a consistent $\NNb$ interaction. For $\NNb$ $S$-states,
they have a drastic effect and bring the relative (${^1S_0}/{^3S_1}$) branching
ratio up to the experimental value, thus resolving the long-standing so-called
``$\rho\pi$'' puzzle. For $\NNb$ $P$-states, their effect is of minor
importance, and discrepancies remain for those ratios involving annihilation
from the $\NNb({^3P_J})$ state to $\rho\pi(l'=2)$.


title: Double-Dipole Excitations in 40Ca

abstract:
  The double-dipole strength distribution in $^{40}$Ca is calculated
microscopically within a model space of 1p1h - and 2p2h excitations. Anharmonic
effects in the centroid energies of the $0^+$- and $2^+$ components are found
to be small, in agreement with experimental observation. Firm conclusions about
the spreading width cannot be drawn, as yet, due to computational limitations
in the number of 2p2h states.


title:
Comparison of Experimental Data to the Relativistic Quantum Molecular
  Dynamics Model For Si+Au Collisions at 14.6 A GeV/c

abstract:
  Predictions from the RQMD model are systematically compared to recently
published charged hadron distributions of AGS Experiment 802 for central Si+Au
collisions at 14.6$A$ GeV/$c$, taking into account both the experimental
trigger condition and acceptance. The main features of the data, including
K$^+$ production, can be understood quantitatively to better than 20\% within
the framework of the model, although several discrepancies are found, most
importantly for the proton spectra.


title: Relativistic Density Dependent Hartree-Fock Approach for Finite Nuclei

abstract:
  The self-energy of the Dirac Brueckner-Hartree-Fock calculation in nuclear
matter is parametrized by introducing density-dependent coupling constants of
isoscalar mesons in the relativistic Hartree-Fock (RHF) approach where
isoscalar meson $\sigma$ , $\omega$ and isovector meson $\pi$, $\rho$
contributions are included. The RHF calculations with density dependent
coupling constants obtained in this way not only reproduce the nuclear matter
saturation properties , but also provide the self-energy with an appropriate
density dependence. The relativistic density dependent Hartree-Fock (RDHF)
approach contains the features of the relativistic G matrix and in the meantime
simplifies the calculation. The ground state properties of spherical nuclei
calculated in the RDHF are in good agreement with the experimental data. The
contribution of isovector mesons $\pi$ and $\rho$ , especially the contribution
of the tensor coupling of $\rho$ meson , are discussed in this paper.


title:
A Resonance Model for pi N -> Y K and pi Delta -> Y K Reactions for Kaon
  Production in Heavy Ion Collisions

abstract:
  In a resonance model the reactions pi N -> Y K and pi Delta -> Y K are
studied. For the reactions pi N -> Lambda K and pi Delta -> Lambda K, the
resonances N(1650)(J^P=1/2^-), N(1710)(1/2^+) and N(1720)(3/2^+) are included
as intermediate states. For the reactions pi N -> Sigma K, the resonances
N(1710)(1/2^+), N(1720)(3/2^+) and Delta(1920)(3/2^+) are considered, while for
the pi Delta -> Sigma K reactions the intermediate resonances are
N(1710)(1/2^+) and N(1720)(3/2^+). Besides these resonances in the s-channel,
the t-channel K^*(892) exchanges are also taken into account as a smooth
background. The relevant coupling constants for the meson-baryon vertices are
obtained (except for Delta(1920)) from the experimental decay branching ratios
of the relevant resonances. All isospin channels of the pi N -> Y K and pi
Delta -> Y K cross sections are calculated. By comparing the calculated results
with the available experimental data, we find that the total cross sections of
the pi N -> Y K reactions can be explained by the resonance model. The pi Delta
-> Y K cross sections, for which no experimental data are available, are
predicted theoretically. Parametrizations of the calculated total cross
sections for all different isospin channels are given for the use of kaon
productions in heavy ion collisions. The differential cross sections are also
studied.


title:
On the Role of Dissipation in the Early Stages of Relativistic Heavy Ion
  Collisions

abstract:
  The influence of the dissipative terms on the conditions of formation and the
characteristic parameters of shock waves in relativistic nuclear collisions is
investigated for three types of equation of state (non linear QHD-1, resonance
gas and lattice QCD). Energy and velocity profiles are obtained in a
one-dimensional model; the duration of the shock phase and width of the shock
front are calculated. It is shown that the presence of a phase transition
results in a strong enhancement of the width of the shock front, which results
in an increase of transparency. This effect, combined with the fact that the
nuclei have a finite size, prevents the energy density to rise to its maximum
value (full stopping) as would be predicted by a non dissipative shock model.


title:
Proton-proton bremsstrahlung below and above pion-threshold: the
  influence of the $\Delta$-isobar

abstract:
  The proton-proton bremsstrahlung is investigated within a coupled-channel
model with the $\Delta$ degree of freedom. The model is consistent with the
$NN$ scattering up to 1 GeV and the $\gamma N\Delta$ vertex determined in the
study of pion photoproduction reactions. It is found that the $\Delta$
excitation can significantly improve the agreements with the $pp \rightarrow
pp\gamma$ at $E_{lab}=280$ MeV. Predictions at $E_{lab}=550$ and $800$ MeV are
presented for future experimental tests.


title: Is Large Weak Mixing in Heavy Nuclei Consistent with Aiomic Experiments?

abstract:
  The hypothesis of a large weak matrix element between single-particle states
in heavy nuclei ($\sim 100$ eV) contradicts the results of atomic PNC
experiments.


title: Two neutrino double beta decay within the $\xi$-approximation

abstract:
  We examine the contributions of odd-parity nuclear operators to the
two-neutrino double beta decay $0^+\rightarrow 0^+$ amplitude, which come from
the $P$-wave Coulomb corrections to the electron wave functions and the recoil
corrections to the nuclear currents. Although they are formally of higher order
in $\alpha Z/2$ or $v/c$ of the nucleon than the usual Fermi and Gamow-Teller
matrix elements, explicit calculations performed within the QRPA show that they
are significant when confronted with the experimental data.


title: Instanton content of finite temperature QCD matter

abstract:
  We investigate the temperature dependence of the instanton content of gluon
fields and their contribution to quark correlation using quenched lattice QCD
and the cooling method. We found a suppression of the topological
susceptibility at finite temperature, agreeing with the PCAC expectation at low
temperature and enhanced suppression for temperatures at and above the
deconfinement transition. For temperatures up to about 334 MeV, the topological
charge correlation agrees well with a single instanton profile, though the size
parameter seems to change across the phase transition. The screening wave
functions for the pion and the rho become slightly more compact at higher
temperatures. Lattice cooling shows no contribution from the instantons to the
screening wave functions at temperatures above the phase transition.


title:
Relativistic nuclear structure effects in quasielastic neutrino
  scattering

abstract:
  Charged-current cross sections are calculated for quasielastic neutrino and
antineutrino scattering using a relativistic meson-nucleon model. We examine
how nuclear-structure effects, such as relativistic random-phase-approximation
(RPA) corrections and momentum-dependent nucleon self-energies, influence the
extraction of the axial form factor of the nucleon. RPA corrections are
important only at low-momentum transfers. In contrast, the momentum dependence
of the relativistic self-energies changes appreciably the value of the
axial-mass parameter, $M_A$, extracted from dipole fits to the axial form
factor. Using Brookhaven's experimental neutrino spectrum we estimate the
sensitivity of M$_A$ to various relativistic nuclear-structure effects.


title:
Induced Parity Nonconserving Interaction and Enhancement of Two-Nucleon
  Parity Nonconserving Forces

abstract:
  Two-nucleon parity nonconserving (PNC) interaction induced by the
single-particle PNC weak potential and the two-nucleon residual strong
interaction is considered. An approximate analytical formula for this Induced
PNC Interaction (IPNCI) between proton and neutron is derived ($Q({\bf r} {\bf
\sigma}_{p} \times {\bf \sigma}_{n}) \delta({\bf r}_{p}-{\bf r}_{n})$), and the
interaction constant is estimated. As a result of coherent contributions from
the nucleons to the PNC potential, IPNCI is an order of magnitude stronger
($\sim A^{1/3}$) than the residual weak two-nucleon interaction and has a
different coordinate and isotopic structure (e.g., the strongest part of IPNCI
does not contribute to the PNC mean field). IPNCI plays an important role in
the formation of PNC effects, e.g., in neutron-nucleus reactions. In that case,
it is a technical way to take into account the contribution of the distant
(small) components of a compound state which dominates the result. The absence
of such enhancement ($\sim A^{1/3}$) in the case of T- and P-odd interaction
completes the picture.


title:
Spin-Isospin Modes in Heavy-Ion Collisions I: Nuclear Matter at Finite
  Temperatures

abstract:
  With a view towards implementation in microscopic transport simulations of
heavy-ion collisions, the properties of spin-isospin modes are studied in
nuclear matter consisting of nucleons and Delta isobars that interact by the
exchange of pi and rho mesons. For a standard p-wave interaction and an
effective g' short-range interaction, the dispersion relations for the spin-
isospin modes, and the associated amplitudes, are calculated at various nuclear
densities and temperatures, within the random-phase approximation. Quantities
of physical interest are then extracted, including the total and partial Delta
decay widths and the Delta cross sections in the nuclear medium. The
self-consistent inclusion of the Delta width has a strong effect on the Delta
cross sections at twice normal nuclear density, as compared with the result of
ignoring the width. Generally, the obtained quantities exhibit a strong density
dependence, but are fairly insensitive to the temperature, at least up to T=25
MeV. Finally, it is described how these in-medium effects may be consistently
included into microscopic transport simulations of nuclear collisions, and the
improvements over previous approaches are discussed.


title: Fragment Flow and the Nuclear Equation of State

abstract:
  We use the Boltzmann-Uehling-Uhlenbeck model with a momentum-dependent
nuclear mean field to simulate the dynamical evolution of heavy ion collisions.
We re-examine the azimuthal anisotropy observable, proposed as sensitive to the
equation of state of nuclear matter. We obtain that this sensitivity is maximal
when the azimuthal anisotropy is calculated for nuclear composite fragments, in
agreement with some previous calculations. As a test case we concentrate on
semi-central $^{197}{\rm Au}\ +\ ^{197}{\rm Au}$ collisions at 400 $A$ MeV.


title:
Pion-Nucleon Scattering and the $\pi$NN Coupling Constant in the Chiral
  Color Dielectric Model

abstract:
  We apply the chiral color dielectric model to low- and medium-energy
scattering within the coupled $\pi$N and $\pi\Delta$ system. Dynamic baryon
states in which quarks are confined by the scalar color-dielectric field are
constructed in Fock space. Spurious motion of the center of mass is eliminated
by constructing momentum eigenstates via a Peierls-Yoccoz projection. The
relativistic Lippmann-Schwinger equation is solved for the complex energies of
the T matrix poles, and the pole positions of the nucleon and delta are used to
fix the few parameters of the model. The $S$- and $P$-wave phase shifts, the
bare N and $\Delta$ masses, the renormalized $\pi$NN and $\pi$N$\Delta$
coupling constants, and the $\pi$NN and $\pi$N$\Delta$ vertex functions are
predicted. nucleon and delta are used to fix the few parameters of the model.
The $S$- and $P$-wave phase shifts, the bare N and $\Delta$ masses, the
renormalized $\pi$NN and $\pi$N$\Delta$ coupling constants, and the $\pi$NN and
$\pi$N$\Delta$ vertex functions are predicted.


title:
Effects of T- and P-odd weak nucleon interaction in nuclei:
  renormalizations due to residual strong interaction, matrix elements between
  compound states and their correlations with P-violating matrix elements

abstract:
  Manifestations of P-,T-odd weak interaction between nucleons in nucleus are
considered. Renormalization of this interaction due to residual strong
interaction is studied. Mean squared matrix elements of P-,T-odd weak
interaction between compound states are calculated. Correlators between
P-,T-odd and P-odd, T-even weak interaction matrix elements between compound
states are considered and estimates for these quantities are obtained.


title: Inclusive Pion Double Charge Exchange above 0.5 GeV

abstract:
  A cascade model has been developed to study pion induced multichannel
reactions (quasielastic, SCX, DCX, absorption and pion production) at pion
energies above 0.5 GeV. Special attention has been paid to pion double charge
exchange. Pion production is a determinant feature in the high energy pion
nucleus reactions, and the DCX signal not related to pion production is
sizeable only at forward angles and for high energy outgoing pions. The
contribution to DCX of the conventional mechanism, with two quasielastic SCX
steps decreases very fast as a function of the energy and reaches very low
values at energies above 0.7 GeV. This opens the opportunity of having sizeable
contributions of exotic mechanisms that are negligible at the delta resonance
energies.


title: Hydrodynamic Evolution of Chirally Symmetric Nuclear Matter

abstract:
  The equation of state of the linear sigma model in the mean field
approximation is used as input in a relativistic hydrodynamical numerical
routine. Longitudinal and transverse energy distributions are calculated and
compared with those obtained from the QHD-I equation of state.


title: Radiative Neutron-Proton Capture in Effective Chiral Lagrangians

abstract:
  We calculate the cross-section for the thermal $n+p\rightarrow d+\gamma$
process in chiral perturbation theory to next-to-next-to-leading order using
heavy-fermion formalism. The exchange current correction is found to be
$(4.5\pm 0.3)~\%$ in amplitude and the chiral perturbation at one-loop order
gives the cross section $\sigma_{th}^{np}=(334\pm 2)\ {\mbox mb}$ which is in
agreement with the experimental value $(334.2\pm 0.5)\ {\mbox mb}$. Together
with the axial charge transitions, this provides a strong support for the power
of chiral Lagrangians for nuclear physics.


title: Eigenmodes of Decay and Discrete Fragmentation Processes

abstract:
  Linear rate equations are used to describe the cascading decay of an initial
heavy cluster into fragments. This representation is based upon a triangular
matrix of transition rates. We expand the state vector of mass multiplicities,
which describes the process, into the biorthonormal basis of eigenmodes
provided by the triangular matrix. When the transition rates have a scaling
property in terms of mass ratios at binary fragmentation vertices, we obtain
solvable models with explicit mathematical properties for the eigenmodes. A
suitable continuous limit provides an interpolation between the solvable
models. It gives a general relationship between the decay products and the
elementary transition rates.


title:
Role of Cloud Renormalization in Convolution Models for EMC and
  Drell-Yan Ratios

abstract:
  Generalizing a recent convolution model of the nucleon which explicitly
conserves charge and momentum we reexamine the influence of an enhanced pion
field in nuclei on EMC and Drell-Yan ratios. Due to wave function
renormalization constants the effect is more than 50% smaller than predicted by
the standard pion excess model. In particular there is no discrepancy between
the EMC data and our results in the x-region which was expected to be most
sensitive to the pion.


title:
Possible doublet mechanism for a regular component of parity violation
  in neutron scattering

abstract:
  A nucleus with octupole deformation of the mean field reveals rotational
doublets with the same angular momentum and opposite parity. Mediated by the
Coriolis-type interaction, the doublet structure leads to a strong regular
component in the parity violation caused by weak interaction. This can explain
sign correlations observed in polarized neutron scattering by $^{232}$Th.


title: Relativistic Meson Spectroscopy and In-Medium Effects

abstract:
  We extend our earlier model of $q\bar q$ mesons using relativistic
quasipotential (QP) wave equations to include open-flavor states and running
quark-gluon coupling effects. Global fits to meson spectra are achieved with
rms deviations from experiment of 43-50 MeV. We examine in-medium effects
through their influence on the confining interaction and predict the confining
strength at which the masses of certain mesons fall below the threshold of
their dominant decay channel.


title: Nuclear Binding Effects in Relativistic Coulomb Sum Rules

abstract:
  We extend the formulation of relativistic Coulomb sum rules to account for
the average effects of nuclear binding on the initial and final states of
ejected nucleons. Relativistic interactions are included by using a Dirac
representation adapted from a vector-scalar field theory. The scalar field
reduces the effective nucleon mass $M^*$ and increases the relativistic effects
of recoil and Fermi motion. We consider two models for the off-shell behavior
of the nuclear electromagnetic current, and demonstrate that the sum rule is
accurate for applications to data over the interesting range of $M^*$ and three
momentum $q$. We further indicate that the form of the sum rule is sufficiently
general to accommodate a broad class of off-shell form factor models.


title: Scaling with no phase transition

abstract:
  The observation of scaling relations in ultra-relativistic nuclear collisions
would not by itself signal that the hot matter produced in these collisions has
passed through a phase transition.


title: Determination of bound state wave functions by a genetic algorithm

abstract:
  We apply a stochastic method of minimizing the ground state energy in
variational calculations of light nuclei using the Refined Resonating Group
Model (RRGM). The method utilizes a bit representation of the width parameters
to be varied. To find the best possible set of width parameters we use
strategies familiar from biological evolution. Very complicated problems can be
solved in this way because the method is intrinsically parallel. The algorithm
can be used on parallel computers with any number of processors without any
change.


title: Color Transparency and the Vanishing Deuterium Shadow

abstract:
  We find that the final state interactions in the $d(e,e'np)$ amplitude depend
strongly on the final momentum of the spectator nucleon. This means that color
transparency effects can be studied at rather low four-momentum transfer
$Q^2\geq$ 4 (GeV/c)$^2$ using un-polarized and polarized deuteron targets.


title: Quantum interference effects in ($\vec e,e'p$) reactions

abstract:
  The response to longitudinally polarized electrons in coincident out-of-plane
($\vec{\mathrm e},{\mathrm e}'{\mathrm p}$) reaction is discussed to study the
role of final state interactions and quantum interference between different
reaction channels, i.e. between direct (quasi) elastic proton emission and
baryon resonance production. The high-energy suppression of this effect due to
colour transparency is also discussed. Results are given for the
$^{12}$C($\vec{\mathrm e},{\mathrm e}'{\mathrm p}$)$^{11}$B$_{\mathrm {g.s.}}$


title:
Production of Strange Clusters and Strange Matter in Nucleus-Nucleus
  Collisions at the AGS

abstract:
  Production probabilities for strange clusters and strange matter in Au+Au
collisions at AGS energy are obtained in the thermal fireball model. The only
parameters of the model, the baryon chemical potential and temperature, were
determined from a description of the rather complete set of hadron yields from
Si+nucleus collisions at the AGS. For the production of light nuclear fragments
and strange clusters the results are similar to recent coalescence model
calculations. Strange matter production with baryon number larger than 10 is
predicted to be much smaller than any current experimental sensitivities.


title: Does the excited state of the $^3$H nucleus exist?

abstract:
  The suggestion is made that the excited state of the $^3 H$ nucleus found out
recently in the reaction $H$ ($^6 He$,$\alpha$) ({\it Pis'ma JETPh\/} {\bf 59}
(1994) 301) has spin and parity $1/2^+$ and the same configuration that the
ground one of $^6 He$. An amplitude of electromagnetic transition to the triton
ground state is strongly suppressed, therefore the excited state cannot be
detected in radiative capture of neutrons by deuterons. It is shown that in an
elastic nd-scattering a resonance associated with the exited state may be
absent due to the destructive interference of potential and resonant scattering
phases.


title:
Revisit of Coulomb effects on pi^{-}/pi^{+} ratio in heavy-ion
  collisions

abstract:
  It is shown that the large $\pi^{-}/\pi^{+}$ ratio at low pion energies
recently observed in the reaction of Au+Au at $E_{beam}/A=1.0$ GeV at SIS/GSI
is due to the strong Coulomb field of the reaction system.


title:
Azimuthal correlations of pions in relativistic heavy ion collisions at
  1 GeV/nucl.

abstract:
  Triple differential cross sections of pions in heavy ion collisions at 1
GeV/nucl. are studied with the IQMD model. After discussing general properties
of $\Delta$ resonance and pion production we focus on azimuthal correlations:
At projectile- and target-rapidities we observe an anticorrelation in the
in-plane transverse momentum between pions and protons. At c.m.-rapidity,
however, we find that high $p_t$ pions are being preferentially emitted
perpendicular to the event-plane. We investigate the causes of those
correlations and their sensitivity on the density and momentum dependence of
the real and imaginary part of the nucleon and pion optical potential.