title: Kaon mass in dense matter

abstract:
  The variation of kaon mass in dense, charge-neutral baryonic matter at
beta-equilibrium has been investigated. The baryon interaction has been
included by means of nonlinear Walecka model, with and without hyperons and the
interaction of kaons with the baryons has been incorporated through the
Nelson-Kaplan model. A self-consistant, one-loop level calculation has been
carried out. We find that at the mean field level, the presence of the hyperons
makes the density-dependence of the kaon mass softer. Thus, the kaon
condensation threshold is pushed up in the baryon density. The loop diagrams
tend to lower the kaon condensation point for lower values of $a_3 m_s$. We
also find that the S-wave kaon-nucleon interaction plays the dominant role in
determining the on-set of kaon condensation and the contribution of the P-wave
interaction is insignificant.


title: Nearthreshold Large $Q^2$ Electroproduction off Polarized Deuteron

abstract:
  The exclusive and inclusive electroproduction off the polarized deuteron is
considered at large $Q^2$ and $x \ge 0.5$. It is shown that the use of a
polarized target will allow to emphasize smaller than average internucleon
distances in the deuteron. As a result, we expect amplification of all the
effects (color transparency, relativistic dynamics, etc.) sensitive to small
internucleon distances. Numerical estimates are given for the processes $e+
\vec d \rightarrow e +p+n$ and $e+ \vec d \rightarrow e +X$.


title:
Antikaon flow in heavy-ion collisions: the effects of absorption and
  mean fields

abstract:
  We study antikaon flow in heavy-ion collisions at SIS energies based on the
relativistic transport model (RVUU 1.0). The production of antikaons from both
baryon-baryon and pion-baryon collisions are included. Taking into account only
elastic and inelastic collisions of the antikaon with nucleons and neglecting
its mean-field potential as in the cascade model, a strong antiflow or
anti-correlation of antikaons with respect to nucleons is seen as a result of
the strong absorption of antikaons by nucleons. However, the antiflow of
antikaons disappears after including also their propagation in the attractive
mean-field potential. The experimental measurement of antikaon flow in
heavy-ion collision will be very useful in shedding lights on the relative
importance of antikaon absorption versus its mean-field potential.


title:
Coherent pion production in neutrino nucleus collision in the 1 GeV
  region

abstract:
  We calculate cross sections for coherent pion production in nuclei induced by
neutrinos and antineutrinos of the electron and muon type. The analogies and
differences between this process and the related ones of coherent pion
production induced by photons, or the (p,n) and $(^3 He, t)$ reactions are
discussed. The process is one of the several ones occurring for intermediate
energy neutrinos, to be considered when detecting atmospheric neutrinos. For
this purpose the results shown here can be easily extrapolated to other
energies and other nuclei.


title: Can one extract source radii from transport theories?

abstract:
  To know the space time evolution of a heavy ion reaction is of great
interest, especially in cases where the measured spectra do not allow to
ascertain the underlying reaction mechanism. In recent times it became popular
to believe that the comparison of Hanbury-Brown Twiss correlation functions
obtained from classical or semiclassical transport theories, like Boltzmann
Uehling Uhlenbeck (BUU), Quantum Molecular Dynamics (QMD), VENUS, RQMD or ARC,
with experiments may provide this insight. It is the purpose of this article to
show that this conjecture encounters serious problems. The models which are
suited to be compared with the experiments at CERN and Brookhaven are not able
to predict a correlation function. Any agreement with existing data has to be
considered as accidental. The models suited for lower energies can in principle
predict correlation functions. The systematic error may be too large to be of
use as far as quantitative conclusions are concerned.


title:
Uncertainties In Direct Neutron Capture Calculations Due To Nuclear
  Structure Models

abstract:
  The prediction of cross sections for nuclei far off stability is crucial in
the field of nuclear astrophysics. For spherical nuclei close to the dripline
the statistical model (Hauser-Feshbach) approach is not applicable and direct
contributions may dominate the cross sections. For neutron-rich, even-even Sn
targets, we compare the resulting neutron capture cross sections when
consistently taking the input for the direct capture calculations from three
different microscopic models. The results underline the sensitivity of cross
sections calculated in the direct model to nuclear structure models which can
lead to high uncertainties when lacking experimental information.


title:
Enhancement of low-mass dileptons in SPS heavy-ion collisions: possible
  evidence for dropping rho meson mass in medium

abstract:
  Dilepton production in proton- and nucleus-induced reactions at SPS energies
is studied in the relativistic transport model using initial conditions
determined by the string dynamics from RQMD. It is found that both the CERES
and HELIOS-3 data for dilepton spectra in proton-nucleus reactions can be well
described by the conventional mechanism of Dalitz decay and direct vector meson
decay. However, to provide a quantitative explanation of the observed dilepton
spectra in central S+Au and S+W collisions requires contributions other than
these direct decays. Introducing a decrease of vector meson masses in hot dense
medium, we find that these heavy-ion data can also be satisfactorily explained.
We also give predictions for Pb+Au collisions at 160 GeV/nucleon using current
CERES mass resolution and acceptance.


title: Pion-Production in Heavy-Ion Collisions at SIS energies

abstract:
  We investigate the production of pions in heavy-ion collisions in the energy
range of $1$ - $2$ GeV/A. The dynamics of the nucleus-nucleus collisions is
described by a set of coupled transport equations of the
Boltzmann-Uehling-Uhlenbeck type for baryons and mesons. Besides the $N(938)$
and the $\Delta(1232)$ we also take into account nucleon resonances up to
masses of $1.9 GeV/c^2$ as well as $\pi$-, $\eta$- and $\rho$-mesons. We study
in detail the influence of the higher baryonic resonances and the
$2\pi$-production channels ($NN\to NN \pi\pi$) on the pion spectra in
comparison to $\pi^-$ data from $Ar + KCl$ collisions at $1.8$ GeV/A and
$\pi^0$-data for $Au+Au$ at 1.0 GeV/A. We, furthermore, present a detailed
comparison of differential pion angular distributions with the BEVALAC data for
Ar + KCl at 1.8 GeV/A. The general agreement obtained indicates that the
overall reactions dynamics is well described by our novel transport approach.


title: The Spectral Line Shape of Exotic Nuclei

abstract:
  The quadrupole strength function of $^{28}O$ is calculated making use of the
SIII interaction, within the framework of continuum-RPA and taking into account
collisions among the nucleons (doorway coupling). The centroid of the giant
resonance is predicted at $\approx 14$ MeV, that is much below the energy
expected for both isoscalar and isovector quadrupole resonances in nuclei along
the stability valley. About half of this width arises from the coupling of the
resonance to the continuum and about half is due to doorway coupling. This
result is similar to that obtained in the study of giant resonances in light,
$\beta$-stable nuclei, and shows the lack of basis for the expectation,
entertained until now in the literature, that continuum decay was the main
damping mechanism of giant resonances in halo nuclei.


title:
The Pauli principle in the soft-photon approach to proton-proton
  bremstrahlung

abstract:
  A relativistic and manifestly gauge-invariant soft-photon amplitude, which is
consistent with the soft-photon theorem and satisfies the Pauli Principle, is
derived for the proton-proton bremsstrahlung process. This soft-photon
amplitude is the first two-u-two-t special amplitude to satisfy all theoretical
constraints. The conventional Low amplitude can be obtained as a special case.
It is demonstrated that previously proposed amplitudes for this process, both
the (u,t) and (s,t) classes, violate the Pauli principle at some level. The
origin of the Pauli principle violation is shown to come from two sources: (i)
For the (s,t) class, the two-s-two-t amplitude transforms into the two-s-two-u
amplitude under the interchange of two initial-state (or final-state) protons.
(ii) For the (u,t) class, the use of an internal emission amplitude determined
from the gauge-invariance constraint alone, without imposition of the Pauli
principle, causes a problem. The resulting internal emission amplitude can
depend upon an electromagnetic factor which is not invariant under the
interchange of the two protons.


title: Baryons as Hybrids of Solitons and Three Quark Bound States

abstract:
  A hybrid model for baryons based on a dynamical interplay between
relativistic three--quark bound states and soliton configurations of mesons is
constructed. The Bethe-Salpeter equation for diquarks and the Faddeev equation
for diquark-quark bound states in the background of a soliton is solved. The
results show that baryons are very much like hybrids containing both, solitonic
meson clouds and three--quark correlations.


title:
Meson-meson scattering: $K\overline{K}$-thresholds and $f_{0}(980) -
  a_{0}(980)$ mixing

abstract:
  We study the influence of mass splitting between the charged and neutral
pions and kaons in the Juelich meson exchange model for $\pi\pi$ and $\pi\eta$
scattering. The calculations are performed in the particle basis, which permits
the use of physical masses for the pseudoscalar mesons and a study of the
distinct thresholds associated with the neutral and the charged kaons. Within
this model we also investigate the isospin violation which arises from the mass
splitting and an apparent violation of G-parity in $\pi\pi$ scattering which
stems from the coupling to the $K\overline{K}$ channel. Nonvanishing cross
sections for $\pi\pi \rightarrow \pi^{0}\eta$ indicate a mixing of the
$f_{0}(980)$ and $a_{0}(980)$ states.


title: Algebraic model of an oblate top

abstract:
  We consider an algebraic treatment of a three-body system. In particular, we
develop the formalism for a system of three identical objects and discuss an
application to nonstrange baryon resonances which are interpreted as
vibrational and rotational excitations of an oblate symmetric top. We derive
closed expressions for a set of elementary form factors that appear in the
calculation of both electromagnetic, strong and weak couplings of baryons.


title:
Phase space characteristics of fragmenting nuclei described as excited
  disordered systems

abstract:
  We investigate the thermodynamical content of a cellular model which
describes nuclear fragmentation as a process taking place in an excited
disordered system. The model which reproduces very well the size distribution
of fragments does not show the existence of a first order phase transition.


title:
Entrance-channel Mass-asymmetry Dependence of Compound-nucleus Formation
  Time in Light Heavy-ion Reactions

abstract:
  The entrance-channel mass-asymmetry dependence of the compound nucleus
formation time in light heavy-ion reactions has been investigated within the
framework of semiclassical dissipative collision models. the model calculations
have been succesfully applied to the formation of the $^{38}$Ar compound
nucleus as populated via the $^{9}$Be+$^{29}$Si, $^{11}$B+$^{27}$Al,
$^{12}$C+$^{26}$Mg and $^{19}$F+$^{19}$F entrance channels. The shape evolution
of several other light composite systems appears to be consistent with the
so-called "Fusion Inhibition Factor" which has been experimentally observed. As
found previously in more massive systems for the fusion-evaporation process,
the entrance-channel mass-asymmetry degree of freedom appears to determine the
competition between the different mechanisms as well as the time scales
involved.


title:
Bulk properties of light deformed nuclei derived from a medium-modified
  meson-exchange interaction

abstract:
  Deformed Hartree-Fock-Bogoliubov calculations for finite nuclei are carried
out. As residual interaction, a Brueckner G-matrix derived from a
meson-exchange potential is taken. Phenomenological medium modifications of the
meson masses are introduced. The binding energies, radii, and deformation
parameters of the Carbon, Oxygen, Neon, and Magnesium isotope chains are found
to be in good agreement with the experimental data.


title: Antiproton production in $pp, dp$ and $dd$ collisions close to threshold

abstract:
  The production of antiprotons in $pp$ collisions is investigated close to
threshold where experimental data about the total cross section are not
available. We analyze the latter reaction within the LUND string model for
inclusive $\bar{p}$ production and within the framework of a one-boson exchange
model for the exclusive reaction $pp \rightarrow ppp\bar{p}$. The application
of our new results to the analysis of subthreshold antiproton production in $d
+ p$ and $d + d$ collisions shows cross sections that are much lower than
expected before. Nevertheless, the comparison of experimental $\bar{p}$
differential cross sections from $d +p$ and $d + d$ is expected to provide
valuable information about a nonnucleonic component in the deuteron
wavefunction.


title: Kaon dispersion relation and flow in relativistic heavy-ion collisions

abstract:
  Within the framework of a relativistic transport model (ART) for heavy-ion
collisions at AGS energies, we examine the effects of kaon dispersion relation
on the transverse flow of kaons and their transverse momentum and azimuthal
angle distributions. We find that the transverse flow is the most sensitive
observable for studying the kaon dispersion relation in dense medium.


title: Baryon Density and the Dilated Chiral Quark Model

abstract:
  We calculate perturbatively the effect of density on hadronic properties
using the chiral quark model implemented by the QCD trace anomaly to see the
possibility of constructing Lorentz invariant Lagrangian at finite density. We
calculate the density dependent masses of the constituent quark, the scalar
field and the pion in one-loop order using the technique of thermo field
dynamics. In the chiral limit, the pion remains massless at finite density. It
is found that the tadpole type corrections lead to the decreasing masses with
increasing baryon density, while the radiative corrections induce
Lorentz-symmetry-breaking terms. We found in the large $N_c$ limit with large
scalar mass that the tadpoles dominate and the mean-field approximation is
reliable, giving rise a Lorentz-invariant Lagrangian with masses decreasing as
the baryon density increases.


title:
New Insights into the Coupling of $\eta $ and $f_1$ Mesons to the
  Nucleon

abstract:
  We show that the contact couplings of neutral pseudoscalar and axial mesons
to the nucleon are proportional to $\Delta s$, the fraction of nucleon spin
carried by the strange quark sea, and thus are strongly suppressed relative to
the couplings of charged mesons to the nucleon. On the other side, recent high
accuracy data on $\eta $ photoproduction at threshold reveal the need for
non--negligibile $\eta NN$ vertices, while fitting $\bar N N$ phase shifts by
means of effective meson exchange potentials requires a substantial presence of
$f_1$ mesons there. We here advocate the idea to attribute the couplings of
neutral pseudoscalar and axial vector mesons to effective triangular diagrams
containig non--strange mesons and demonstrate its usefulness in describing
available data.


title: Bose-Einstein Correlations from Opaque Sources

abstract:
  Bose-Einstein correlations in relativistic heavy ion collisions are very
different for opaque sources than fortransparent ones. The Bose-Einstein radius
parameters measured in two-particle correlation functions depend sensitively on
the mean free path of the particles. In particular we find that the outward
radius for an opaque source is smaller than the sidewards radius for
sufficiently short duration of emission. A long duration of emission can
compensate the opacity reduction of the longitudinal radius parameter and
explain the experimental measurements of very similar side- and outward radius
parameters.


title: Many--Particle Correlations in Relativistic Nuclear Collisions

abstract:
  Many--particle correlations due to Bose-Einstein interference are studied in
ultrarelativistic heavy--ion collisions. We calculate the higher order
correlation functions from the 2--particle correlation function by assuming
that the source is emitting particles incoherently. In particular
parametrizations of and relations between longitudinal, sidewards, outwards and
invariant radii and corresponding momenta are discussed. The results are
especially useful in low statistics measurements of higher order correlation
functions. We evaluate the three--pion correlation function recently measured
by NA44 and predict the 2--pion--2--kaon correlation function. Finally, many
particle Coulomb corrections are discussed.


title:
Charge Symmetry Breaking in the Valence Quark Distributions of the
  Nucleon

abstract:
  Using a quark model, we study the effect of charge symmetry breaking on the
valence quark distributions of the nucleon. The effect due to quark mass
differences and the Coulomb interaction of the electrically charged quarks is
calculated and, in contrast to recent claims, found to be small. In addition,
we investigate the effect of charge symmetry breaking in the confining
interaction, and in the perturbative evolution equations used to relate the
quark model distributions to experiment. We find that both these effects are
small, and that the strong charge symmetry breaking effect included in the
scalar confining interactions may be distinguishable from that generated by
quark mass differences.


title: $J/\Psi$ suppression in nuclear collisions at SPS energies

abstract:
  We have carried out a first calculation of $J/\Psi$ production from nuclear
collisions within the covariant transport approach HSD, which has been very
successful in describing both hadronic and electromagnetic observables from
heavy-ion collisions at intermediate and high energies. The production of
$J/\Psi$'s is based on the Lund string fragmentation model, while its
interactions with hadrons are included by conventional cascade-type two-body
collisions. Adopting 6 mb for the $J/\Psi$-baryon cross sections and 3 mb for
the $J/\Psi$-meson cross sections above the $D\bar{D}$ threshold, we find that
data on $J/\Psi$ suppression from both proton-nucleus and nucleus-nucleus
collisions (including Pb + Pb) can be explained without assuming the formation
of a quark-gluon plasma in these collisions. Our microscopic studies thus
confirm the suggestion of Gavin et al. that $J/\Psi$ suppression observed in
nuclear collisions is largely due to absorption by comovers, i.e., the produced
mesons.


title: Non-nucleonic Effects Studied by Nuclear Moments

abstract:
  Measured magnetic moments of single-particle states in the Pb region differ
significantly from their Schmidt values. We discuss the reasons for this in
terms of meson-exchange currents, isobar currents, core polarisation and other
effects.


title: The inclusive transverse response of nuclear matter

abstract:
  The electromagnetic inclusive transverse response of nuclear matter at
saturation density is studied within the correlated basis function perturbation
theory for momentum transfers q from 300 to 550 MeV/c. The correlation operator
includes a Jastrow component, accounting for the short range repulsion, as well
as longer range spin, tensor and isospin ones. The Schiavilla-
Pandharipande-Riska model for the two-body electromagnetic currents, satisfying
the continuity equation with realistic v_14 potentials, is adopted. Currents
due to intermediate Delta-isobar excitations, are also included. The global
contribution of the two-body currents turns out to be positive and provides an
enhancement of the one-body transverse response ranging from about 20% for the
lower momenta to about 10% for the higher ones. This finding is in agreement
with the Green's Function Monte Carlo studies of the transverse Euclidean
response in A=3,4 nuclei and contradicts previous results obtained within the
Fermi gas and shell models. The tensor-isospin component of the correlation is
found to be the leading responsible for such a behavior. The nuclear matter
response is compared to recent experimental data on 40Ca and 56Fe.


title: Nucleation of Quark--Gluon Plasma Droplets

abstract:
  The energy densities achieved during central collisions of large nuclei at
the AGS may be high enough to allow the formation of quark--gluon plasma. We
propose that most collisions at AGS energies produce superheated hadronic
matter, but in rare events a droplet of quark--gluon plasma is nucleated. We
estimate the probability of this to occur based on homogeneous and
inhomogeneous nucleation theory and discuss possible experimental signals.


title:
Hanbury-Brown/Twiss Interferometry for Relativistic Heavy-Ion
  Collisions: Theoretical Aspects

abstract:
  I discuss two-particle intensity interferometry as a method to extract from
measured 1- and 2-particle momentum spectra information on the space-time
geometry and dynamics of the particle emitting source. Particular attention is
given to the rapid expansion and short lifetime of the sources created in
relativistic heavy-ion collisions. Model-independent expressions for the HBT
size parameters in terms of the space-time variances of the source are derived,
and a new parametrization of the correlation function is suggested which allows
to separate the transverse, longitudinal and temporal extension of the source
and to measure its transverse and longitudinal expansion velocity. The effects
of resonance decays are also discussed.


title:
Hot Spots and Turbulent Initial Conditions of Quark-Gluon Plasmas in
  Nuclear Collisions

abstract:
  As a result of multiple mini-jet production, initial conditions of the QCD
plasma formed in ultrarelativistic nuclear collisions may be inhomogeneous,
with large fluctuations of the local energy density (hot spots), and turbulent,
with a chaotic initial transverse velocity field. Assuming rapid local
thermalization, the evolution of such plasmas is computed using longitudinal
boost-invariant 3+1-dimensional hydrodynamics. We compare the evolution in case
that the speed of sound in the plasma is constant to one resulting from an
equation of state involving a strong first order transition, with a minimum of
the velocity of sound as a function of energy density. We find that azimuthally
asymmetric fluctuations and correlations of the transverse energy flow can
develop in both cases due to the initial inhomogeneities. Hot spots also
enhance significantly high-transverse momenta direct photon yields. In the case
with a phase transition, the hadronization surface evolves into an unusual
foam-like structure. Also in that case, we find that hadronization is
considerably delayed relative to the ideal gas case, just as previous studies
have found for homogeneous initial conditions. The time-delay signature of a
rapid cross-over transition region in the QCD equation of state (as observable
via meson interferometry) is thus found to be remarkably robust to
uncertainties in the initial conditions in heavy-ion reactions.


title:
Elimination of the vacuum instability for finite nuclei in the
  relativistic $\sigma$-$\omega$ model

abstract:
  The $\sigma$-$\omega$ model of nuclei is studied at leading order in the
$1/N$ expansion thereby introducing the self consistent Hartree approximation,
the Dirac sea corrections and the one fermion loop meson self energies in a
unified way. For simplicity, the Dirac sea is further treated within a
semiclassical expansion to all orders. The well-known Landau pole vacuum
instability appearing in this kind of theories is removed by means of a scheme
recently proposed in this context. The effect of such removal on the low
momentum effective parameters of the model, relevant to describe nuclear matter
and finite nuclei, is analyzed. The one fermion loop meson self energies are
found to have a sizeable contribution to these parameters. However, such
contribution turns out to come mostly from the Landau poles and is thus
spurious. We conclude that the fermionic loop can only be introduced
consistently in the $\sigma$-$\omega$ nuclear model if the Landau pole problem
is dealt with properly.


title: Triplet np Final State Interactions at Large Momentum Transfers

abstract:
  Using the simple relation between the np scattering and bound state wave
functions, the spin-triplet contributions to the pp -> pi+ (pn) and backward dp
-> p(pn) reactions are estimated for low np excitation energies. The good
agreement with the pion production data at 400 and 450 MeV over a range of
angles shows that spin-singlet final states cannot be more than of the order of
10%. On the other hand it is seen that the spin-singlet states must provide
about 30% of the strength in pion production at 1 GeV as well as
deuteron-proton backward scattering at 1.6 GeV.


title:
Theoretical Response to the Discovery of Deeply Bound Pionic States in
  208Pb(d,3He) reactions

abstract:
  Recently, deeply bound pionic states were found experimentally in (d, $^3$He)
reactions on $^{208}$Pb. They found an isolated peak structure in the bound
region below the pion production threshold. We study theoretically these
excitation functions in (d, $^3$He) reactions on $^{208}$Pb at T$_d$=600 MeV.
We found very good agreement with the (d, $^3$He) excitation functions and
could identify the underlying structures of the pionic states. We study the
energy dependence of the (d, $^3$He) reactions and the change of the excitation
functions with the incident energy.


title: High-momentum proton removal from 16O and the (e,e'p) cross section

abstract:
  The cross section for the removal of high-momentum protons from 16O is
calculated for high missing energies. The admixture of high-momentum nucleons
in the 16O ground state is obtained by calculating the single-hole spectral
function directly in the finite nucleus with the inclusion of short-range and
tensor correlations induced by a realistic meson-exchange interaction. The
presence of high-momentum nucleons in the transition to final states in 15N at
60-100 MeV missing energy is converted to the coincidence cross section for the
(e,e'p) reaction by including the coupling to the electromagnetic probe and the
final state interactions of the outgoing proton in the same way as in the
standard analysis of the experimental data. Detectable cross sections for the
removal of a single proton at these high missing energies are obtained which
are considerably larger at higher missing momentum than the corresponding cross
sections for the p-wave quasihole transitions. Cross sections for these
quasihole transitions are compared with the most recent experimental data
available.


title: Phase Transition in the chiral $\sigma$-$\omega$ model with dilatons

abstract:
  We investigate the properties of different modifications to the linear
$\sigma$-model (including a dilaton field associated with broken scale
invariance) at finite baryon density $\rho$ and nonzero temperature $T$. The
explicit breaking of chiral symmetry and the way the vector meson mass is
generated are significant for the appearance of a phase of nearly vanishing
nucleon mass besides the solution describing normal nuclear matter. The
elimination of the abnormal solution prohibits the onset of a chiral phase
transition but allows to lower the compressibility to a reasonable range. The
repulsive contributions from the vector mesons are responsible for the wide
range of stability of the normal phase in the $(\mu,T)$-plane. The abnormal
solution becomes not only energetically preferable to the normal state at high
temperature or density, but also mechanically stable due to the inclusion of
dilatons.


title: Pion-pair formation and the pion dispersion relation in a hot pion gas

abstract:
  The possibility of pion--pair formation in a hot pion gas, based on the
bosonic gap equation, is pointed out and discussed in detail. The critical
temperature for condensation of pion pairs (Evans--Rashid transition) is
determined as a function of the pion density. As for fermions, this phase
transition is signaled by the appearance of a pole in the two--particle
propagator. In bose systems there exists a second, lower critical temperature,
associated with the appearance of the single--particle condensate. Between the
two critical temperatures the pion dispersion relation changes from the usual
quasiparticle dispersion to a Bogoliubov--like dispersion relation at low
momenta. This generalizes the non-relativistic result for an attractive bose
gas by Evans et al. Possible consequences for the inclusive pion spectra
measured in heavy--ion collisions at ultra--relativistic energies are
discussed.


title:
Contribution of real and virtual Pions to nuclear Photoabsorption at
  Intermediate Energies

abstract:
  The universal curve $\sigma /A$ of nuclear photoabsorption is investigated
within a Fermi gas model of nuclear matter. An energy range from pion threshold
up to 400 MeV is considered. The interactions between nucleon, pion, $\Delta
$-isobar and photon are considered in the non-relativistic approximation with
corrections of the order $1/M$ taken into account with respect to proton mass.
Analytical expressions are obtained, in which the influence of nuclear
correlations, two-nucleon contributions and relativistic corrections is studied
explicitely. An extension of the model calculation to nucleon knock-out
reactions is discussed.


title: The Nuclear-Matter Response in the Quark String-flip Model

abstract:
  Nuclear matter is modeled directly in terms of its constituent quarks. A
many-body string-flip potential is used that confines quarks within hadrons,
enables the hadrons to separate without generating van der Waals forces, and is
symmetric in all quark coordinates. We present variational Monte Carlo results
for the ground-state properties of large, three-dimensional systems. A phase
transition from nuclear to quark matter is observed which is characterized by a
dramatic rearrangement of strings. We report on exact calculations of the
dynamic response of many-quark systems in one spatial dimension. At low density
and small momentum transfers the response is substantially larger than that of
a free Fermi gas of quarks; this suggests that there is a coherent response
from all the quarks inside the hadron. This coherence, however, is incomplete,
as the response is suppressed relative to that of a free Fermi gas of nucleons
due to the internal quark substructure of the hadron.


title: Confinement, Diquarks and Goldstone's theorem

abstract:
  Determinations of the gluon propagator in the continuum and in lattice
simulations are compared. A systematic truncation procedure for the quark
Dyson-Schwinger and bound state Bethe-Salpeter equations is described. The
procedure ensures the flavour-octet axial-vector Ward identity is satisfied
order-by-order, thereby guaranteeing the preservation of Goldstone's theorem;
and identifies a mechanism that simultaneously ensures the absence of diquarks
in QCD and their presence in QCD$^{N_c=2}$, where the colour singlet diquark is
the ``baryon'' of the theory.


title:
Finite Nuclei in a Relativistic Mean-Field Model with Derivative
  Couplings

abstract:
  We study finite nuclei, at the mean-field level, using the Zimanyi-Moskowski
model and one of its variations (the ZM3 model). We calculate energy levels and
ground-state properties in nuclei where the mean-field approach is reliable.
The role played by the spin-orbit potential in sorting out mean-field model
descriptions is emphasized.


title: Reaction Rates of neutron capture by Li- and Be-isotopes

abstract:
  Neutron capture by neutron-rich Li- and Be-isotopes plays a role in big--bang
nucleosynthesis, especially in its inhomogeneous version and in the
$\alpha$--process occurring in supernovae. New reaction rates for
$^{7,8}$Li(n,$\gamma$)$^{8,9}$Li and $^{9,10,11}$Be(n,$\gamma$)$^{10,11,12}$Be
have been consistently calculated using direct capture for the nonresonant part
and the Breit-Wigner formula for the resonant part. The spectroscopic factors,
spin/parity assignments and excitation energies of the final bound and initial
resonant states have been taken from existing experimental data whenever
possible. For unstable nuclei where this information is not experimentally
available the shell model was used to determine these quantities.


title: On the Flavor Structure of the Constituent Quark

abstract:
  We discuss the dressing of constituent quarks with a pseudoscalar meson cloud
within the effective chiral quark model. SU(3) flavor symmetry breaking effects
are included explicitly. Our results are compared with those of the traditional
meson cloud approach in which pions are coupled to the nucleon. The pionic
dressing of the constituent quarks explains the experimentally observed
violation of the Gottfried Sum Rule and leads to an enhanced nonperturbative
sea of quark-antiquark pairs in the constituent quark and consequently in the
nucleon. We find 2.5 times more pions and 10-15 times more kaons in the nucleon
than in the traditional picture.


title: Nuclear Shell Model by the Quantum Monte Carlo Diagonalization Method

abstract:
  The feasibility of shell-model calculations is radically extended by the
Quantum Monte Carlo Diagonalization method with various essential improvements.
The major improvements are made in the sampling for the generation of
shell-model basis vectors, and in the restoration of symmetries such as angular
momentum and isospin. Consequently the level structure of low-lying states can
be studied with realistic interactions. After testing this method on $^{24}$Mg,
we present first results for energy levels and $E2$ properties of $^{64}$Ge,
indicating its large and $\gamma$-soft deformation.


title: The Problem of Matter Stability in the Nambu--Jona-Lasinio Model

abstract:
  We reinvestigate the conditions for stable matter solutions in the
Nambu--Jona-Lasinio (NJL) model. In mean field approximation the NJL model can
be regarded as an extension of the Walecka mean field model to include negative
energy fermion states. While this extension is necessary to allow for a chiral
phase transition, it was found some time ago that at the same time it destroys
the wanted saturation properties of the Walecka model. We reformulate this
problem in terms of the thermodynamic potential and find that there is indeed a
connection between these two features. We show that the minimum of the
thermodynamic potential which corresponds to stable nuclear matter in the
Walecka model is shifted from a finite to zero effective fermion mass in the
chiral NJL model. This shift is closely related to the chiral phase transition.
Under certain conditions the shifted minima may still lead to stable matter
solutions but only in the chirally restored phase. We discuss a possible
interpretation of these solutions as a schematic bag model description.


title: Quadrupole-quadrupole interaction calculations which include N=2 mixing

abstract:
  We carry out a study of the study of the $Q \cdot Q$ interaction in a model
space which consists of several nucleons in an open shell and all $2 \hbar
\omega$ excitations. This interaction is $ -t (X_o/2) Q \cdot Q$, where for t=1
we get the `accepted strength'. In the $0p$ space, the spectrum would scale
with $t$. In this space, the $2^+_1$ and $2^+_2$ states of $^{10}$Be are
degenerate, as are the [330] and [411] sets of $J=0^+, 1^+$ and $2^+$ triplets.
When $2 \hbar \omega$ admixtures are included, the degeneracies are removed.
For $t \geq 1.8$ we have new ground state and a new $2_1^+$ state. These are
states in which two particles are excited from the $0p$ to the $1s-0d$ shell.
There is no mixing of these 2p-2h states with the other states. For these 2p-2h
states the occupancy for 0s,0p,1s-0d and 1p-of are 4,4,2 and 0 respectively.


title:
No-core shell-model calculations with starting- energy-independent
  multi-valued effective interactions

abstract:
  Large-space no-core shell model calculations have been performed for A=3-6
nuclei, using a starting-energy-independent two-body effective interaction
derived by application of the Lee-Suzuki similarity transformation. This
transformation can be performed by direct calculation or by different iteration
procedures, which are described. A possible way of reducing the auxiliary
potential influence on the two-body effective interaction has also been
introduced. The many-body effects have been partially taken into account by
employing the recently introduced multi-valued effective interaction approach.
Dependence of the He5 energy levels on the harmonic-oscillator frequency as
well as on the size of the model space has been studied. The Reid 93
nucleon-nucleon potential has been used in the study, but results have also
been obtained using the Nijmegen II potential for comparison.


title: Electroproduction of the Roper resonance and the constituent quark model

abstract:
  A parameter-free evaluation of the $N - P_{11}(1440)$ electromagnetic
transition form factors is performed within a light-front constituent quark
model, using for the first time the eigenfunctions of a mass operator which
generates a large amount of configuration mixing in baryon wave functions. A
one-body electromagnetic current, which includes the phenomenological
constituent quark form factors already determined from an analysis of pion and
nucleon experimental data, is adopted. For $Q^2$ up to few $(GeV/c)^2$, at
variance with the enhancement found in the elastic channel, the effect of
configuration mixing results in a significant suppression of the calculated
helicity amplitudes with respect to both relativistic and non-relativistic
calculations, based on a simple gaussian-like ansatz for the baryon wave
functions.


title:
Probing the Origin of the EMC Effect via Tagged Structure Functions of
  the Deuteron

abstract:
  We demonstrate that measurement of tagged structure functions of the deuteron
in (e,e'N) semi-inclusive reactions can discriminate between different
hypotheses on the origin of the nuclear EMC effect. By choosing extreme
backward kinematics for the spectator nucleon to minimize effects from the
deuteron wave function and final state interactions, one can isolate the
modifications in the structure of the bound nucleon within the impulse
approximation. The same reaction can be used to extract the large-x neutron to
proton structure function ratio.


title: Medium Modification of Nucleon Properties in Skyrme Model

abstract:
  A Skyrme type Lagrangian for a skyrmion imbedded in a baryon rich environment
is proposed. The dependence of static nucleon properties and nucleon - nucleon
tensor interaction on nuclear density is investigated.


title: Kaon versus Antikaon Production at SIS Energies

abstract:
  We analyse the production and propagation of kaons and antikaons in Ni + Ni
reactions from 0.8--1.85 GeV/u within a coupled channel transport approach
including the channels $BB \to K^+YN, \pi B\to K^+Y, BB \to NN K \bar{K}, \pi
B\to N K\bar{K}, K^+B\to K^+B, \bar{K} B\to \bar{K}B, Y N\to \bar{K} NN, \pi
\pi\to K \bar{K}$ as well as $\pi Y\to \bar{K}N$ and $\bar{K} N\to \pi Y$ for
the antikaon absorption. Whereas the experimental $K^+$ spectra can be
reproduced without introducing any selfenergies for the mesons in Ni + Ni
collisions from 0.8 to 1.8 GeV/u, the $K^-$ yield is underestimated by a factor
of 5--7 at 1.66 and 1.85 GeV/u. However, introducing density dependent antikaon
masses as proposed by Kaplan and Nelson, the antikaon spectra can be reasonably
well described.


title:
Threshold kaon photo- and electroproduction in SU(3) baryon chiral
  perturbation theory

abstract:
  We calculate the processes $\gamma p \to K^0 \Sigma^+ , K^+ \Sigma^0, K^+
\Lambda$ in three flavor heavy baryon chiral perturbation theory to one loop.
Some low--energy constants are fixed from single baryon properties while others
are estimated by means of resonance saturation. The total cross sections are
comparable with the few existing data points in the threshold region. The
angular dependences of the recoil polarization of the $\Lambda$ and $\Sigma^0$
show most features of the ones measured at ELSA. We also predict the isovector
charge radius of the $\Sigma^+$, $< r^2_V >_{\Sigma^+} = (0.30 \pm 0.03) fm^2$.


title: CVC in Particle Physics

abstract:
  We review the hypothesis of the conserved vector current (CVC) within the
Standard Model. In addition to the classic tests, such as pion beta decay and
neutrino scattering, we mention recent tests involving LEP data. As well as
providing a clear indication that the isovector current is not conserved,
rho-omega mixing offers a fascinating opportunity to study CP violation at
B-factories and we outline these ideas. Finally we briefly touch on a new
approach to mass generation in the Standard Model which, for example, leads to
the up-down mass difference which breaks CVC.


title: Current algebra and soft pionic modes in asymmetric quark matter

abstract:
  Pionic excitations are analyzed in isospin-asymmetric Fermi gas of
constituent quarks. It is found that in addition to the usual pionic
excitations, there exists a very low collective mode with quantum numbers of
the charged pion (spin-isospin sound). In the chiral limit the excitation
energy of one of the modes scales as the current quark mass, and the mode
saturates current-algebraic sum rules. This is in agreement with predictions of
current algebra for isospin-asymmetric medium.


title:
Modeling of Nucleon-Nucleon Potentials, Quantum Inversion versus Meson
  Exchange Pictures

abstract:
  The notion of interacting elementary particles for low and medium energy
nuclear physics is associated with definitions of potential operators. In
principle, this potential carries the rich substructure consisting of quarks
and gluons and thus may be deduced from some microscopic model. In this spirit
we propose a boson exchange potential from a nonlinear quantum field theory.
Essentially, the meson propagators and form factors of conventional models are
replaced by amplitudes derived from the dynamics of self-interacting mesons in
terms of solitary fields. Contrary to deduction, we position the inversion
approach. Using Gel'fand-Levitan and Marchenko inversion we compute local,
energy-independent potentials from experimental phase shifts for various
partial waves. Both potential models give excellent results for on-shell NN
scattering data. In the off-shell domain we study both potential models in PP
Bremsstrahlung, elastic nucleon-nucleus scattering and triton binding energy
calculations. It remains surprising that for all observables the inversion and
microscopic meson exchange potentials are equivalent in their reproduction of
data. Finally, we look for another realm of elementary interactions where
inversion and meson exchange models can be applied with the hope to find more
sensitivity to discern substructure dynamics.


title:
Soft Neutron Productions - a Window to the Final State Interactions in
  DIS

abstract:
  We analyze production of soft neutrons ($E_n\le 10MeV$) in deep inelastic
scattering and conclude that the recent E-665 data indicate strong suppression
of the final state interactions in DIS at high energies. Hence we suggest that
studies of the energy dependence of the soft neutrons yields would provide a
sensitive probe of the dynamics of the final state interactions in DIS.


title:
Open Charm Production and its Lepton Pair Signal in High Energy Nuclear
  Collisions

abstract:
  Open charm production at the initial and the pre-equilibrium stages in
nuclear collisions is studied. The pre-equilibrium contribution to open charm
production in $A+A$ collisions at $\sqrt s=200 AGeV$ is shown to be very
sensitive to correlations between momenta and space-time coordinates of the
minijets produced after the initial collision. A minimal correlation model
based on the uncertainty principle is introduced, and leads only to a small
pre-equilibrium charm yield as compared with initial yields. Opposite-sign
lepton pairs $ee, e\mu$ and $\mu\mu$ from open charm decay in $p+A$ reactions
at $\sqrt s=200$ AGeV are proposed as a measure of nuclear shadowing effects.
Via an approximate scaling, the ratio of the spectra from $p+A$ collisions to
those from $pp$ collisions is shown to reflect the shadowing function well.
Finally it is shown that the required measurements are feasible at RHIC.


title: Topics Concerning the Quadrupole-Quadrupole Interaction

abstract:
  We address some properties of the quadrupole-quadrupole ($Q \cdot Q$)
interaction in nuclear studies. We first consider how to restore $SU(3)$
symmetry even though we use only coordinate and not momentum terms. Using the
Hamiltonian $H=\sum_i (p^2/2m + m/2 \omega^2 r_i^2) -\chi \sum_{i < j}Q(i)
\cdot Q(j) - \chi/2 \sum_i Q(i) \cdot Q(i)$ with $Q_{\mu}=r^2 Y_{2,\mu}$, we
find that only 2/3 of the single-particle splitting
($\epsilon_{0d}-\epsilon_{1s}$) comes from the diagonal term of $Q \cdot Q$
-the remaining 1/3 comes from the interaction of the valence nucleus with the
core. On another topic, a previously derived relation, using $Q \cdot Q$,
between isovector orbital $B(M1)$ (scissors mode) and the ``difference''
($B(E2, isoscalar)-B(E2, isovector)$) is discussed. It is shown that one needs
the isovector $B(E2)$ in order that one get the correct limit as one goes to
nuclei sufficiently far from stability so that one subshell (neutron or proton)
is closed.


title: Intrinsic operators for the electromagnetic nuclear current

abstract:
  The intrinsic electromagnetic nuclear meson exchange charge and current
operators arising from a separation of the center-of-mass motion are derived
for a one-boson-exchange model for the nuclear interaction with scalar,
pseudoscalar and vector meson exchange including leading order relativistic
terms. Explicit expressions for the meson exchange operators corresponding to
the different meson types are given in detail for a two-nucleon system. These
intrinsic operators are to be evaluated between intrinsic wave functions in
their center-of-mass frame.


title: Squeezed condensate of gluons and $\eta-\eta'$ mass difference

abstract:
  We consider a mechanism to create the $\eta - \eta'$ mass difference by the
gluon anomaly in a squeezed vacuum. We find that the mass shift of the $\eta_0$
governing this mass difference is determined by the magnetic part of the gluon
condensate. For the squeezed vacuum this magnetic part coincides with the total
gluon condensate, so that we get a relation between the gluon condensate and
the mass shift of the $\eta_0$ as a function of the strong coupling constant
$\alpha_s$. The values of the gluon condensate obtained through this relation
are compared with the value by Shifman, Vainshtein and Zakharov and the recent
update values by Narison.


title: On the symmetries of the 1+1 dimensional relativistic fluid dynamics

abstract:
  A very intuitive description of nucleus-nucleus collision phenomena is
provided by the relativistic fluid dynamics. We consider a 1+1 dimensional
relativistic imperfect fluid flow to approximate the high energy heavy ion
collision. The article investigates the application of the continuous symmetry
group on the relativistic fluid energy-momentum tensor conservation equations
in the ultrarelativistic limit $\gamma \rightarrow \infty$.


title:
Studies in the statistical and thermal properties of hadronic matter
  under some extreme conditions

abstract:
  The thermal and statistical properties of hadronic matter under some extreme
conditions are investigated using an exactly solvable canonical ensemble model.
A unified model describing both the fragmentation of nuclei and the thermal
properties of hadronic matter is developed. Simple expressions are obtained for
quantities such as the hadronic equation of state, specific heat,
compressibility, entropy, and excitation energy as a function of temperature
and density. These expressions encompass the fermionic aspect of nucleons, such
as degeneracy pressure and Fermi energy at low temperatures and the ideal gas
laws at high temperatures and low density. Expressions are developed which
connect these two extremes with behavior that resembles an ideal Bose gas with
its associated Bose condensation. In the thermodynamic limit, an infinite
cluster exists below a certain critical condition in a manner similar to the
sudden appearance of the infinite cluster in percolation theory. The importance
of multiplicity fluctuations is discussed and some recent data from the EOS
collaboration on critical point behavior of nuclei can be accounted for using
simple expressions obtained from the model.


title:
Tagging nucleon structure functions by heavy particle detection in deep
  inelastic electron-ion scattering

abstract:
  It is shown that in deep inelastic electron - ion collisions the detection,
in coincidence with the scattered electron, of a nucleus A-1 in the ground
state, as well as a nucleon and a nucleus A-2 also in the ground state, may
provide unique information on several long standing problems, such as the
origin of the EMC effect, the possible medium modifications of the nucleon
structure functions, and the nature of Nucleon-Nucleon correlations.


title: QCD Vacuum Changes in Nuclei

abstract:
  In this talk, I discuss how the changes in the QCD vacuum induced by
increasing nuclear matter density affect nuclear properties under normal as
well as extreme conditions. The quark condensate which is the order parameter
for the mode in which chiral symmetry is manifested is expected to change as
matter density or temperature is changed. The topics discussed are ``BR
scaling," its connection to the structure of nuclei in Landau's Fermi liquid
theory and a variety of consequences on such nuclear properties as effective
nucleon mass, nuclear gyromagnetic ratios, $g_A^\star$, axial-charge
transitions in nuclei and on the fluctuations of nuclear matter into the
strange-flavor direction as observed in heavy-ion collisions. I will also
present a simple explanation of the recent dilepton data in the CERN-CERES
heavy-ion experiments involving densities greater than that of nuclear matter
and of the Indiana results on the longitudinally polarized proton scattering
from heavy nuclei, evidencing dropping vector-meson masses in medium which can
be interpreted as signaling an aspect of chiral symmetry restoration in dense
medium. The test of BR scaling provides a bridge between the physics of extreme
conditions (e.g. relativistic heavy-ion collisions) and the physics of normal
conditions which has conventional descriptions, thereby setting the stage for
formulating many-body theory for nuclear matter starting from an effective
chiral Lagrangian.


title: $J/\psi$ and $\psi'$ suppression by comovers in Pb+Pb collisions

abstract:
  Measurements of $\psi$ and $\psi'$ production at the CERN SPS are compared to
predictions based on a hadronic model of charmonium suppression. Detailed
information is presented to facilitate comparison to other analyses.
Sensitivity of these conclusions to the model parameters is discussed.


title: Stability of the Heaviest Nuclei on Spontaneous-Fission and Alpha-Decay

abstract:
  Spontaneous-fission half-lives of the heaviest even-even nuclei are evaluated
and compared with their alpha-decay mode. Calculations of spontaneous-fission
half-lives are performed in the dynamical way with potential energy obtained by
the macroscopic-microscopic method and the inertia tensor obtained by the
cranking approximation. The alpha-decay half-lives are calculated for the same
region of nuclei by use of the Viola and Seaborg formula. The ground-state
properties such as mean square radii and electric quadrupole moments are also
studied. From the analysis of spontaneous-fission half-life values it is found
that a peninsula of deformed metastable superheavy nuclei near Z=106 and N=162
is separated from an island of the spherical superheavy, around the doubly
magic nucleus with Z=114 and N=184, by a trench in the vicinity of neutron
number N=170.


title: Temperature determination from the lattice gas model

abstract:
  Determination of temperature from experimental data has become important in
searches for critical phenomena in heavy ion collisions. Widely used methods
are ratios of isotopes (which rely on chemical and thermal equilibrium),
population ratios of excited states etc. Using the lattice gas model we propose
a new observable: $n_{ch}/Z$ where $n_{ch}$ is the charge multiplicity and $Z$
is the charge of the fragmenting system. We show that the reduced multiplicity
is a good measure of the average temperature of the fragmenting system.


title:
Strangeness in the nucleon and the ratio of proton-to-neutron
  neutrino-induced quasi-elastic yield

abstract:
  The electroweak form factors of the nucleon as obtained within a three flavor
pseudoscalar vector meson soliton model are employed to predict the ratio of
the proton and neutron yields from $^{12}C$, which are induced by quasi-elastic
neutrino reactions. These predictions are found to vary only moderately in the
parameter space allowed by the model. The antineutrino flux of the up-coming
experiment determining this ratio was previously overestimated. The
corresponding correction is shown to have only a small effect on the predicted
ratio. However, it is found that the experimental result for the ratio
crucially depends on an accurate measurement of the energy of the knocked out
nucleon.


title: Friction Coefficient for Deep-Inelastic Heavy-Ion Collisions

abstract:
  Based on the microscopic model, the friction coefficient for the relative
motion of nuclei in deep-inelastic heavy-ion collisions is calculated. The
radial dependence of the friction coefficient is studied and the results are
compared with those found by other methods. Based on this result, it was
demonstrated that the kinetic energy dissipation in deep-inelastic heavy-ion
collisions is a gradual process which takes up a significant part of a reaction
time. An advantage of the suggested method is that it allows one to consider
the relative motion of nuclei and the intrinsic motion self-consistently.


title: The Imaginary Part of Nucleon Self-energy in hot nuclear matter

abstract:
  A semiphenomenological approach to the nucleon self-energy in nuclear matter
at finite temperatures is followed. It combines elements of Thermo Field
Dynamics for the treatment of finite temperature with a model for the
self-energy, which evaluates the second order diagrams taking the needed
dynamics of the NN interaction from experiment. The approach proved to be
accurate at zero temperature to reproduce Im(Sigma) and other properties of
nucleons in matter. In the present case we apply it to determine Im(Sigma) at
finite temperatures. An effective NN cross section is deduced which can be
easily used in analyses of heavy ion reactions.


title: Self-Consistent Velocity Dependent Effective Interactions

abstract:
  The theory of self-consistent effective interactions in nuclei is extended
for a system with a velocity dependent mean potential. By means of the field
coupling method, we present a general prescription to derive effective
interactions which are consistent with the mean potential. For a deformed
system with the conventional pairing field, the velocity dependent effective
interactions are derived as the multipole pairing interactions in
doubly-stretched coordinates. They are applied to the microscopic analysis of
the giant dipole resonances (GDR's) of ${}^{148,154}Sm$, the first excited
$2^+$ states of Sn isotopes and the first excited $3^-$ states of Mo isotopes.
It is clarified that the interactions play crucial roles in describing the
splitting and structure of GDR peaks, in restoring the energy weighted sum
rule, and in reducing the values of $B(E\lambda)$.


title: On the Coulomb and higher-order sum rules in the relativistic Fermi gas

abstract:
  Two different methods for establishing a space-like Coulomb sum rule for the
relativistic Fermi gas are compared. Both of them divide the charge response by
a normalizing factor such that the reduced response thus obtained fulfills the
sum rule at large momentum transfer. To determine the factor, in the first
approach one exploits the scaling property of the longitudinal response
function, while in the second one enforces the completeness of the states in
the space-like domain via the Foldy-Wouthuysen transformation. The
energy-weighted and the squared-energy-weighted sum rules for the reduced
responses are explored as well and the extension to momentum distributions that
are more general than a step-function is also considered. The two methods yield
reduced responses and Coulomb sum rules that saturate in the non-Pauli-blocked
region, which can hardly be distinguished for Fermi momenta appropriate to
atomic nuclei. Notably the sum rule obtained in the Foldy-Wouthuysen approach
coincides with the well known non-relativistic one. Only at quite large
momentum transfers (say 1 GeV/c) does a modest softening of the
Foldy-Wouthuysen reduced response with respect to that obtained in the scaling
framework show up. The two responses have the same half-width to second order
in the Fermi momentum expansion. However, when distributions extending to
momenta larger than that at the Fermi surface are employed, then in both
methods the Coulomb sum rule saturates only if the normalizing factors are
appropriately modified to account for the high momentum components of the
nucleons.


title: Pairing correlations in N~Z pf-shell nuclei

abstract:
  We perform Shell Model Monte Carlo calculations to study pair correlations in
the ground states of $N=Z$ nuclei with masses A=48-60. We find that $T=1$,
$J^{\pi}=0^+$ proton-neutron correlations play an important, and even dominant
role, in the ground states of odd-odd $N=Z$ nuclei, in agreement with
experiment. By studying pairing in the ground states of $^{52-58}$Fe, we
observe that the isovector proton-neutron correlations decrease rapidly with
increasing neutron excess. In contrast, both the proton, and trivially the
neutron correlations increase as neutrons are added.
  We also study the thermal properties and the temperature dependence of pair
correlations for $^{50}$Mn and $^{52}$Fe as exemplars of odd-odd and even-even
$N=Z$ nuclei. While for $^{52}$Fe results are similar to those obtained for
other even-even nuclei in this mass range, the properties of $^{50}$Mn at low
temperatures are strongly influenced by isovector neutron-proton pairing. In
coexistence with these isovector pair correlations, our calculations also
indicate an excess of isoscalar proton-neutron pairing over the mean-field
values. The isovector neutron-proton correlations rapidly decrease with
temperatures and vanish for temperatures above $T=700$ keV, while the isovector
correlations among like nucleons persist to higher temperatures. Related to the
quenching of the isovector proton-neutron correlations, the average isospin
decreases from 1, appropriate for the ground state, to 0 as the temperature
increases.


title:
Low-energy interaction of composite spin-half systems with scalar and
  vector fields

abstract:
  We consider a composite spin-half particle moving in spatially-varying scalar
and vector fields. The vector field is assumed to couple to a conserved charge,
but no assumption is made about either the structure of the composite or its
coupling to the scalar field. A general form for the piece of the spin-orbit
interaction of the composite with the scalar and vector fields which is
first-order in momentum transfer ${\bf Q}$ and second-order in the fields is
derived.


title: Photon electroproduction off nuclei in the $\Delta$-resonance region

abstract:
  The cross section for the $A(e,e'\gamma)A$ reaction is calculated,
investigating the contribution from the nuclear target with respect to the
radiative corrections from the electron. The reaction mechanism is studied for
photon emission in the $\Delta$-resonance region, varying the scattering
geometry and analyzing the most favourable kinematical conditions to extract
information on the nuclear system.


title:
Photocouplings of nucleon resonances with gluon and pion exchange
  currents

abstract:
  Photocouplings for the nucleon resonances most relevant to total
photoabsorption are calculated in a constituent quark model including gluon and
pion exchange. The sensitivity of the results to the different ingredients of
the model is discussed.


title:
Nuclear Density-Dependent Effective Coupling Constants in the Mean-Field
  Theory

abstract:
  It is shown that the equation of state of nuclear matter can be determined
within the mean-field theory of $\sigma \omega$ model provided only that the
nucleon effective mass curve is given. We use a family of the possible nucleon
effective mass curves that reproduce the empirical saturation point in the
calculation of the nuclear binding energy curves in order to obtain
density-dependent effective coupling constants. The resulting density-dependent
coupling constants may be used to study a possible equation of state of nuclear
system at high density or neutron matter. Within the constraints used in this
paper to $M^*$ of nuclear matter at saturation point and zero density, neutron
matter of large incompressibility is strongly bound at high density while soft
neutron matter is weakly bound at low density. The study also exhibits the
importance of surface vibration modes in the study of nuclear equation of
state.


title: Delta Decay in the Nuclear Medium

abstract:
  The $\Delta$ decay in the nuclear medium is calculated in the relativistic
meson-nucleon model. The delta spreading width is calculated and compared with
the Pauli-blocked $\pi$N decay width. The influence of relativistic mean fields
is also studied. We stress the importance of understanding the delta spreading
width in interpreting experiments involving delta resonances.


title:
Spin Observables in Consistent Relativistic Models of (e, e'p) and
  (gamma, p) Reactions

abstract:
  Single nucleon knockout reactions must be described in a consistent framework
in order to extract information about nuclear structure and reaction
mechanisms. Consistent relativistic models for the direct knockout contribution
to the (e, e'p) and (gamma, p) reactions have been developed and used
previously to examine existing momentum distribution and cross section data for
the two reactions^{1}. We present results of calculations of spin observables
obtained from these models of (e, e'p) and (gamma, p) reactions. For the (e,
e'p) reaction we consider the importance of the choice of kinematics and show
that perpendicular kinematics result in distributions with relatively large
cross sections and comparatively large polarizations. In the (gamma, p)
reactions the photon asymmetry and proton polarization are not very sensitive
to changes in model ingredients when the incident photon energy is less than
100 MeV. For higher energies these observables show increasing sensitivity to
modifications of both the bound and continuum wave functions.


title: QCD Sum Rule for $\Lambda$(1405)

abstract:
  Motivated by the recently constructed interpolation field for S$_{11}$(1535),
we propose a new interpolating field for $\Lambda$(1405). Using this current,
we calculate the mass of $\Lambda$(1405) based on the conventional QCD sum rule
analysis. By calculating the Wilson coefficients up to dimension 8 operators
and taking into account the mass corrections from s-quark, we find the
calculated mass of $\Lambda$(1405) to be very close to its experimental value.


title:
Electromagnetic N-$\Delta$ transition form factors in a covariant
  quark-diquark model

abstract:
  The electromagnetic N-$\Delta$ transition form factors are calculated in the
framework of a formally covariant constituent diquark model. As a spin-3/2
particle the $\Delta$ is assumed to be a bound state of a quark and an
axial-vector diquark. The wave function is obtained from a diquark-quark
Salpeter equation with an instantaneous quark exchange potential. The three
transition form factors are calculated for momentum transfers squared from the
pseudothreshold $(M_\Delta-M_N)^2$ up to $-2 (GeV/c)^2$. The magnetic form
factor is in qualitative agreement with experiment. We find very interesting
results for the ratios E2/M1 and C2/M1.


title: Baryon-to-entropy ratio in very high energy nuclear collisions

abstract:
  We compute as a function of rapidity $y$ the baryon number carried by quarks
and antiquarks with $p_T > p_0 \approx$ 2 GeV produced in Pb+Pb collisions at
TeV energies. The computation is carried out in lowest order QCD perturbation
theory using structure functions compatible with HERA results. At $p_0=2$ GeV
the initial gluon density is both transversally saturated and thermalised in
the sense that the energy/gluon equals to that of an ideal gas with the same
energy density. Even at these high energies the initial net baryon number
density at $y=0$ at $\tau=0.1$ fm will be more than the normal nuclear matter
density but the baryon-to-entropy ratio is only $(B-\bar B)/S\sim 1/5000$.
Further evolution of the system is discussed and the final baryon-to-entropy
ratio is estimated.


title: Photon Spin and the Shape of the Two-Photon Correlation Function

abstract:
  We use the covariant current formalism to derive the general form of the
2-photon correlation function for fully chaotic sources. Motivated by the
recent discussion in the literature we concentrate on the effects from the
photon spin on the correlator. We show that for locally thermalized expanding
sources, like those expected to be created in relativistic heavy ion
collisions, the only change relative to 2-pion interferometry is a statistical
factor 1/2 for the overall strength of the correlation which results from the
experimental averaging over the photon spin.


title: The Representation Transformation of Multiquark Wave Functions

abstract:
  It is shown that the representation transformations of multiquark wave
functions between different coupling schemes are just the Racah coefficients of
the permutation group. The transformation coefficients between the flavor-spin
(FS) and the color-spin (CS) schemes are obtained. As an example, the expansion
of the physical bases in terms of symmetry bases in the CS scheme are given for
the interesting cases $YIJ = 201, 210, 000$.


title: Meson and Quark Degrees of Freedom and the Radius of the Deuteron

abstract:
  The existing experimental data for the deuteron charge radius are discussed.
The data of elastic electron scattering are inconsistent with the value
obtained in a recent atomic physics experiment. Theoretical predictions based
on a nonrelativistic description of the deuteron with realistic nucleon-nucleon
potentials and with a rather complete set of meson-exchange contributions to
the charge operator are presented. Corrections arising from the quark-gluon
substructure of the nucleon are explored in a nonrelativistic quark model; the
quark-gluon corrections, not accounted for by meson exchange, are small. Our
prediction for the deuteron charge radius favors the value of a recent atomic
physics experiment.


title: Coulomb Effect on phi->K+K- Invariant Mass

abstract:
  We demonstrate that coulomb interaction between a static charge source and K+
and K- from phi-meson decay could introduce systematic shift in the phi
invariant mass reconstructed from the K+K- pair.


title:
Nucleon Scattering from Very Light Nuclei: Intermediate Energy
  Expansions for Transition Potentials and Breakup Processes

abstract:
  Optical potentials for elastic p-d scattering and the coupled processes
p+$^3$He $\rightarrow$ p+$^3$He and p+$^3$He $\rightarrow$ d+d are derived in
the Faddeev-Yakubovsky framework with special emphasis on leading order terms,
which are expected to be valid at intermediate energies. In addition, equations
for the fragmentations $^3$He(p,ppp)n and $^3$He(p,pp)d are derived within the
same framework. Again leading order terms for intermediate energies are
considered.


title: Vector meson radiation in relativistic heavy-ion collisions

abstract:
  The sigma-omega model in mean-field approximation where the meson fields are
treated classically, describes much of observed nuclear structure and has been
employed to describe the nuclear equation of state up to the quark-gluon phase
transition. The acceleration of the meson sources, for example, in relativistic
heavy-ion collisions, should result in bremsstrahlung-like radiation of the
meson fields. The many mesons emitted serve to justify the use of classical
meson fields. The slowing of the nuclei during the collision is modeled here as
a smooth transition from initial to final velocity. Under ultra-relativistic
conditions, vector radiation dominates. The angular distribution of energy flux
shows a characteristic shape. It appears that if the vector meson field couples
to the conserved baryon current, independent of the baryonic degrees of
freedom, this mechanism will contribute to the radiation seen in relativistic
heavy-ion collisions. The possible influence of the quark-gluon plasma is also
considered.


title: Photoproduction of pions and etas in nuclei

abstract:
  We calculate the cross sections for inclusive one-pion, two-pion and eta
photoproduction in nuclei in the photon energy range from 300 MeV to 900 MeV
within the framework of a semi-classical BUU transport model. Our results are
compared with existing experimental data and discussed with respect to a
calculation of the total photoabsorption cross section.


title: Chiral Symmetry and the Nucleon-Nucleon Interaction

abstract:
  The main progress in the field of nucleon-nucleon (NN) potentials, which we
have seen in recent years, is the construction of some very quantitative
(high-quality/high-precision) NN potentials. These potentials will serve as
excellent input for microscopic nuclear structure calculations and will allow
for a systematic investigation of off-shell effects. After this enormous
quantitative work, it is now time to re-think the NN problem in fundamental
terms. We need a derivation of the nuclear force which observes Lorentz
invariance and the symmetries of QCD.


title:
Dibaryon Condensate in Nuclear Matter and Neutron Stars: Exact Analysis
  in One-Dimensional Models

abstract:
  We investigate dense nuclear matter with a dibaryon Bose-Einstein condensate
as a possible intermediate state before the quark-gluon phase transition. An
exact analysis of this state of matter is presented in a one-dimensional model.
The analysis is based on a reduction of the quantization rules for the N-body
problem to N coupled algebraic transcendental equations. We observe that when
the Fermi momentum approaches the resonance momentum, the one-particle
distribution function increases near the Fermi surface. When the Fermi momentum
is increased beyond the resonance momentum, the equation of state becomes
softer. The observed behavior can be interpreted in terms of formation of a
Bose-Einstein condensate of two-fermion resonances (dibaryons). In cold nuclear
matter, it should occur if 2(m_N + epsilon_F) is greater or equal to m_D, where
m_N and m_D are respectively the nucleon and dibaryon masses and epsilon_F is
the nucleon Fermi energy.


title: QCD Sum Rules: Isospin Symmetry Breakings in Pion-Nucleon Couplings

abstract:
  We use the method of QCD sum rules in the presence of an external pion field
to investigate isospin symmetry breakings in pion-nucleon couplings. Possible
manifestations of such isospin symmetry breaking are examined in the context of
low-energy nucleon-nucleon ($NN$) scattering. We discuss numerical results in
relation to both the existing data and other theoretical predictions.


title:
Elliptical flow -- a signature for early pressure in ultrarelativistic
  nucleus-nucleus collisions

abstract:
  Elliptical energy flow patterns in non-central Au(11.7AGeV) on Au reactions
have been studied employing the RQMD model. The strength of these azimuthal
asymmetries is calculated comparing the results in two different modes of RQMD
(mean field and cascade). It is found that the elliptical flow which is readily
observable with current experimental detectors may help to distinguish
different reasonable expansion scenarios for baryon-dense matter. The final
asymmetries are very sensitive to the pressure at maximum compression, because
they involve a partial cancelation between early squeeze-out and subsequent
flow in the reaction plane. This cancelation can be expected to occur in a
broad energy region covered by the current heavy ion fixed-target programs at
BNL and at CERN.


title:
Influence of the in-medium pion dispersion relation in heavy ion
  collisions

abstract:
  We investigate the influence of medium corrections to the pion dispersion
relation on the pion dynamics in intermediate energy heavy ion collisions. To
do so a pion potential is extracted from the in-medium dispersion relation and
used in QMD calculations and thus we take care of both, real and imaginary part
of the pion optical potential. The potentials are determined from different
sources, i.e. from the $\Delta$--hole model and from phenomenological
approaches. Depending on the strength of the potential a reduction of the
anti-correlation of pion and nucleon flow in non-central collisions is observed
as well as an enhancement of the high energetic yield in transverse pion
spectra. A comparison to experiments, in particular to $p_t$-spectra for the
reaction Ca+Ca at 1 GeV/nucleon and the pion in-plane flow in Ne+Pb collisions
at 800 MeV/nucleon, generally favours a weak potential.


title: Dirac-Foldy term and the electromagnetic polarizability of the neutron

abstract:
  We reconsider the Dirac-Foldy contribution $\mu^2/m$ to the neutron electric
polarizability. Using a Dirac equation approach to neutron-nucleus scattering,
we review the definitions of Compton continuum ($\bar{\alpha}$), classical
static ($\alpha^n_E$), and Schr\"{o}dinger ($\alpha_{Sch}$) polarizabilities
and discuss in some detail their relationship. The latter $\alpha_{Sch}$ is the
value of the neutron electric polarizability as obtained from an analysis using
the Schr\"{o}dinger equation. We find in particular $\alpha_{Sch} =
\bar{\alpha} - \mu^2/m$ , where $\mu$ is the magnitude of the magnetic moment
of a neutron of mass $m$. However, we argue that the static polarizability
$\alpha^n_E$ is correctly defined in the rest frame of the particle, leading to
the conclusion that twice the Dirac-Foldy contribution should be added to
$\alpha_{Sch}$ to obtain the static polarizability $\alpha^n_E$.


title:
From Nuclear Astrophysics to Superheavy Elements: Predictions for Nuclei
  Beyond Our Shores

abstract:
  Properties of 8,979 nuclei ranging from oxygen-16 to Z = 136, A = 339 and
extending from the proton drip line to the neutron drip line have been
calculated by use of the 1992 version of the finite-range droplet model. The
calculated quantities include the ground-state mass, deformation, microscopic
correction, odd-proton and odd-neutron spins and parities, proton and neutron
pairing gaps, binding energy, one- and two-neutron separation energies,
quantities related to beta-delayed one- and two-neutron emission probabilities,
beta-decay energy release and half-life with respect to Gamow-Teller decay,
one- and two-proton separation energies, and alpha-decay energy release and
half-life. For 1,654 nuclei heavier than oxygen-16 whose masses were known
experimentally in 1989 and which were included in the adjustment of model
constants, the theoretical error is 0.669 MeV. For 371 additional nuclei
heavier than oxygen-16 whose masses have been measured between 1989 and 1996
and which were not used in the adjustment of the model constants, the
theoretical error is 0.570 MeV. We also discuss the extrapolateability of two
other recent global models of the macroscopic-microscopic type, and conclude
with a brief discussion of the recently discovered rock of metastable
superheavy nuclei near Z = 110, A = 272 that had been correctly predicted by
macroscopic-microscopic models.


title:
Probability of a Solution to the Solar Neutrino Problem Within the
  Minimal Standard Model

abstract:
  Tests, independent of any solar model, can be made of whether solar neutrino
experiments are consistent with the minimal Standard Model (stable, massless
neutrinos). If the experimental uncertainties are correctly estimated and the
sun is generating energy by light-element fusion in quasi-static equilibrium,
the probability of a standard-physics solution is less than 2%. Even when the
luminosity constraint is abandoned, the probability is not more than 4%. The
sensitivity of the conclusions to input parameters is explored.


title: Effective kaon mass in dense baryonic matter: role of correlations

abstract:
  We evaluate the effective kaon mass in dense nuclear matter. Pauli blocking
and nucleon-nucleon short-range correlations are incorporated. The effects of
short-range correlations are shown to be moderate and figure importantly only
at densities larger than 2 times normal nuclear density. We discuss the
relations between the present results and the results obtained in
next-to-next-to-leading order chiral perturbation theory (${{\cal O} (Q^3)}$,
where $Q$ is the characteristic small energy-momentum scale probed). We also
discuss mean-field aspects, with some remarks on the relation between the
short-range correlations and the four-Fermi contact terms in the chiral
effective Lagrangian.


title: Superheavy nuclei in selfconsistent nuclear calculations

abstract:
  The shell structure of superheavy nuclei is investigated within various
parametrizations of relativistic and nonrelativistic nuclear mean field models.
The heaviest known even-even nucleus 264Hs is used as a benchmark to estimate
the predictive value of the models. From that starting point, doubly magic
spherical nuclei are searched in the region Z=110-140 and N=134-298. They are
found at (Z=114, N=184), (Z=120, N=172), or at (Z=126, N=184), depending on the
parametrization.


title: Microscopic calculations of stopping and flow from 160AMeV to 160AGeV

abstract:
  The behavior of hadronic matter at high baryon densities is studied within
Ultrarelativistic Quantum Molecular Dynamics (URQMD). Baryonic stopping is
observed for Au+Au collisions from SIS up to SPS energies. The excitation
function of flow shows strong sensitivities to the underlying equation of state
(EOS), allowing for systematic studies of the EOS. Effects of a density
dependent pole of the $\rho$-meson propagator on dilepton spectra are studied
for different systems and centralities at CERN energies.


title: A theoretical view of practical problems in interferometry

abstract:
  Interferometry is discussed in terms of the representation of the source. In
particular, scale-invariant 1-d hydrodynamics is revisited, and extended to the
case of unequal transverse masses. It is argued that that kaon emission occurs
over a short time interval. Exact results for models of two- and
three-dimensional flow are presented, which exhibit altered scaling laws. Such
qualitative trends, together with other observables, are vital if one is to
draw conclusions about the source.


title: Neutron Capture and Neutron Halos

abstract:
  The connection between the neutron halo observed in light neutron rich nuclei
and the neutron radiative capture process is outlined. We show how nuclear
structure information such as spectroscopic factors and external components of
the radial wave function of loosely bound states can be derived from the
neutron capture cross section. The link between the direct radiative capture
and the Coulomb dissociation process is elucidated.


title:
Effects of state dependent correlations on nucleon density and momentum
  distributions

abstract:
  The proton momentum and density distributions of closed shell nuclei are
calculated within a model treating short--range correlations up to first order
in the cluster expansion. The validity of the model is verified by comparing
the results obtained with purely scalar correlations with those produced by
finite nuclei Fermi Hypernetted Chain calculations. State dependent
correlations are used to calculate momentum and density distributions of 12C,
16O, 40Ca, and 48Ca, and the effects of their tensor components are studied.


title:
Fission barriers and asymmetric ground states in the relativistic mean
  field theory

abstract:
  The symmetric and asymmetric fission path for 240Pu, 232Th, and 226Ra is
investigated within the relativistic mean field model. Standard
parametrizations which are well fitted to nuclear ground state properties are
found to deliver reasonable qualitative and quantitative features of fission,
comparable to similar nonrelativstic calculations. Furthermore, stable octupole
deformations in the ground states of Radium isotopes are investigated. They are
found in a series of isotopes, qualitatively in agreement with nonrelativistic
models. But the quantitative details differ amongst the models and between the
various relativsitic parametrizations.


title: Electromagnetic Production of the Hypertriton

abstract:
  Kaon photoproduction on He3, gamma + He3 --> K+ + Hypertriton, is studied in
the framework of the impulse approximation. Realistic He3 wave functions
obtained as solutions of Faddeev equations with the Reid soft-core potential
are used along with different Hypertriton wave functions. Results are compared
for several elementary operator models, which can successfully describe the
elementary kaon production off the proton up to a photon lab energy of k = 2.2
GeV. It is found that the corresponding cross sections are small, of the order
of several nanobarns. It is also shown that the influence of Fermi motion is
important, while the effect of different off-shell assumptions on the cross
section is not too significant.


title: Collective transition densities in neutron-rich nuclei

abstract:
  Quadrupole transition densities in neutron-rich nuclei in the vicinity of the
neutron drip-line are calculated in the framework of the Random Phase
Approximation. The continuum is treated by expansion in oscillator functions.
We focus on the states which contribute to the usual Giant Quadrupole
Resonance, and not on the low-lying strength which is also expected in such
nuclei and whose collective character is still under debate. We find that, due
to the large neutron skin in these nuclei, the isoscalar and isovector modes
are in general strongly mixed. We further show that the transition densities
corresponding to the GQR states can be reasonably well described by the
collective model in terms of in phase and out of phase oscillations of neutron
and proton densities which have different radii.


title: Electromagnetic Properties of the Delta(1232)

abstract:
  We calculate the electromagnetic moments and radii of the Delta(1232) in the
nonrelativistic quark model, including two-body exchange currents. We show that
two-body exchange currents lead to nonvanishing Delta and N-->Delta transition
quadrupole moments even if the wave functions have no D-state admixture. The
usual explanation based on the single-quark transition model involves D-state
admixtures but no exchange currents. We derive a parameter- free relation
between the N-->Delta transition quadrupole moment and the neutron charge
radius: Q(N-->Delta) = r^2(neutron)/sqrt(2). Furthermore, we calculate the M1
and E2 amplitudes for the process photon + N -->Delta. We find that the E2
amplitude receives sizeable contributions from exchange currents. These are
more important than the ones which result from D-state admixtures due to tensor
forces between quarks if a reasonable quark core radius of about 0.6 fm is
used. We obtain a ratio of E2/M1=-3.5%.


title: Skyrme-Model $\pi NN$ Form Factor and Nucleon-Nucleon Interaction

abstract:
  We apply the strong $\pi NN$ form factor, which emerges from the Skyrme
model, in the two-nucleon system using a one-boson-exchange (OBE) model for the
nucleon-nucleon (NN) interaction. Deuteron properties and phase parameters of
NN scattering are reproduced well. In contrast to the form factor of monopole
shape that is traditionally used in OBE models, the Skyrme form factor leaves
low momentum transfers essentially unaffected while it suppresses the
high-momentum region strongly. It turns out that this behavior is very
appropriate for models of the NN interaction and makes possible to use a soft
pion form factor in the NN system. As a consequence, the $\pi N$ and the $NN$
systems can be described using the same soft $\pi NN$ form factor, which is
impossible with the monopole.


title:
Signatures of dense hadronic matter in ultrarelativistic heavy ion
  reactions

abstract:
  The behavior of hadronic matter at high baryon densities is studied within
Ultrarelativistic Quantum Molecular Dynamics (URQMD). Baryonic stopping is
observed for Au+Au collisions from SIS up to SPS energies. The excitation
function of flow shows strong sensitivities to the underlying equation of state
(EOS), allowing for systematic studies of the EOS. Dilepton spectra are
calculated with and without shifting the $\rho$ pole. Except for S+Au
collisions our calculations reproduce the CERES data.


title: A new class of Hanbury-Brown/Twiss parameters

abstract:
  In heavy ion collisions resonances can create strong non-Gaussian effects in
the 2-pion correlation data. Hence, the commonly used Gaussian fit parameters
do not fully characterize these correlators. We suggest a different set of HBT
parameters which does not presuppose a particular shape of the correlator and
allows to extract additional (non-Gaussian) information. Within a simple model
for an expanding source including resonance decays it is shown that this
additional information provides a clean distinction between scenarios with and
without transverse flow.


title:
Off-shell effects in the energy dependence of the Be7(p,gamma)B8
  astrophysical S factor

abstract:
  I show that off-shell effects, like antisymmetrization and Be-7 distortions,
can significantly influence the energy dependence of the nonresonant
Be7(p,gamma)B8 astrophysical S factor at higher energies. The proper treatment
of these effects results in a vitrually flat E1 component of the S factor at
E_cm = 0.3-1.5 MeV energies in the present eight-body model. The energy
dependence of the nonresonant S factor, predicted by the present model, is in
agreement with the low-energy direct capture data and the existing high-energy
Coulomb dissociation data. Irrespective of whether or not the present energy
dependence is correct, off-shell effects can cause 15--20% changes in the value
of S(0) extrapolated from high-energy (E_cm > 0.7 MeV) data.


title: Neutron-Proton Correlations in an Exactly Solvable Model

abstract:
  We examine isovector and isoscalar neutron-proton correlations in an exactly
solvable model based on the algebra SO(8). We look particularly closely at
Gamow-Teller strength and double beta decay, both to isolate the effects of the
two kinds of pairing and to test two approximation schemes: the renormalized
neutron-proton QRPA (RQRPA) and generalized BCS theory. When isoscalar pairing
correlations become strong enough a phase transition occurs and the dependence
of the Gamow-Teller beta+ strength on isospin changes in a dramatic and
unfamiliar way, actually increasing as neutrons are added to an N=Z core.
Renormalization eliminates the well-known instabilities that plague the QRPA as
the phase transition is approached, but only by unnaturally suppressing the
isoscalar correlations. Generalized BCS theory, on the other hand, reproduces
the Gamow-Teller strength more accurately in the isoscalar phase than in the
usual isovector phase, even though its predictions for energies are equally
good everywhere. It also mixes T=0 and T=1 pairing, but only on the isoscalar
side of the phase transition.


title: On description of the direct nucleon decay of giant resonances

abstract:
  A semimicroscopical approach is formulated to describe the direct nucleon
decay of various giant resonances in intermediate and heavy mass spherical
nuclei. The approach consists in: (i) the exact continuum-RPA calculations for
amplitudes of the reactions accompanied by excitation and the nucleon decay of
the collective particle-hole states (doorway states); (ii) the Breit-Wigner
parametrization of the RPA reaction-amplitudes in the vicinity of the giant
giant-resonance energy and evaluation of the doorway-state parameter (the
energy, entrance and partial nucleon, escape widths); (iii) the
phenomenological consideration for the doorway-state coupling to many-particle
configurations with the use of reasonable statistical assumptions and
derivation on this base the expressions for the energy-averaged reaction
amplitudes. The nuclear mean field and quasiparticle interaction are the input
quantities for calculations. Examples of description for the direct nucleon
decay of a number of giant resonances in the $^{208}Pb$ parent nucleus are
given together with the comparison with corresponding experimental data.


title: K_{l 3} and \pi_{e 3} transition form factors

abstract:
  $K_{\ell 3}$ and $\pi_{e 3}$ transition form factors are calculated as an
application of Dyson-Schwinger equations. The role of nonanalytic contributions
to the quark--W-boson vertex is elucidated. A one-parameter model for this
vertex provides a uniformly good description of these transitions, including
the value of the scalar form factor of the kaon at the Callan-Treiman point.
The $K_{\ell 3}$ form factors, $f_\pm^K$, are approximately linear on $t\in
[m_e^2,m_\mu^2]$ and have approximately the same slope. $f_-^K(0)$ is a measure
of the Euclidean constituent-quark mass ratio: $M^E_s/M^E_u$. In the isospin
symmetric limit: $-f_+^\pi(0)= F_\pi(t)$, the electromagnetic pion form factor,
and $f_-^\pi(t)\equiv 0$.


title:
K+(K0)- Condensation in Highly Dense Matter with the Relativistic
  Mean-Field Theory

abstract:
  Properties of dense hadronic matter including strange particles are studied
within the relativistic mean-field theory (RMFT). The possibility of kaon
condensation is reexamined, and a simple condition is found for the parameters
included in RMFT.


title:
Short-range interactions in an effective field theory approach for
  nucleon-nucleon scattering

abstract:
  We investigate in detail the effect of making the range of the ``contact''
interaction used in effective field theory (EFT) calculations of NN scattering
finite. This is done in both an effective field theory with explicit pions, and
one where the pions have been integrated out. In both cases we calculate NN
scattering in the ${}^1 S_0$ channel using potentials which are second-order in
the EFT expansion. The contact interactions present in the EFT Lagrangian are
made finite by use of a square-well regulator. We find that there is an optimal
radius for this regulator, at which second-order corrections to the EFT are
identically zero; for radii near optimal these second-order corrections are
small. The cutoff EFTs which result from this procedure appear to be valid for
momenta up to about 100 MeV/c. We also find that the radius of the square well
cannot be reduced to zero if the theory is to reproduce both the experimental
scattering length and effective range. Indeed, we show that, if the NN
potential is the sum of a one-pion exchange piece and a short-range
interaction, then the short-range piece must extend out beyond 1.1 fm,
regardless of its particular form.


title: Relativistic Dynamics and the Deuteron Axial Current

abstract:
  The deuteron axial current is sensitive both to the form of the
implementation of relativistic dynamics as well as to the details of the
deuteron D state at moderate momentum transfer, making it a natural partner to
the magnetic form factor for exploring details of nucleon-nucleon dynamics and
associated electroweak properties.


title:
Electromagnetic Corrections to Pi Pi Scattering: Some Lessons for the
  Implementation of Meson Exchange Models

abstract:
  The leading non-Coulombic electromagnetic contributions to pi pi s-wave
scattering lengths are computed in Chiral Perturbation Theory. It is shown that
these corrections are zeroth order in the chiral expansion and associated with
electromagnetic contact terms in the effective Lagrangian, i.e. that they do
not involve explicit photon fields in the low-energy effective theory. It is
pointed out that, if one followed the standard meson-exchange-model ansatz for
removing electromagnetic effects, i.e. of subtracting contributions associated
with explicit photon exchange and radiative corrections, as determined by the
photon coupling vertices of the effective hadronic theory, one would completely
miss these contributions and arrive at the erroneous conclusion that the strong
interactions exhibited very large isospin breaking in pi pi scattering.
Implications for electromagnetic "subtraction" procedures in other hadronic
systems and the utility of the effective Lagrangian method for avoiding such
errors are obvious.


title: More Effective Field Theory for Nonrelativistic Scattering

abstract:
  An effective field theory treatment of nucleon-nucleon scattering at low
energy shows much promise and could prove a useful tool in the study of nuclear
matter at both ordinary and extreme densities. The analysis is complicated by
the existence a large length scale --- the scattering length --- which arises
due to couplings in the short distance theory being near critical values. I
show how this can be dealt with by introducing an explicit s-channel state in
the effective field theory. The procedure is worked out analytically in a toy
example. I then demonstrate that a simple effective field theory excellently
reproduces the 1S_0 np phase shift up to the pion production threshold.


title: Some New Results on the H Dibaryon in the Quark Cluster Model

abstract:
  The H dibaryon channel, (I=0,J=0,S=-2), is revisited in the non-relativistic
quark cluster model (NRQCM) using a basis extended beyond the usual set of
baryon cluster pairs to include an explicit spatially symmetric 6q state,
analogous in structure to the MIT bag model H. We find that the binding
predicted using the two-baryon basis alone is significantly deepened by the
addition of the additional 6q configuration. The NRQCM thus appears, contrary
to earlier findings, to be incompatible with the experimental information
available for this channel.


title: Inversion Potentials for Meson-Nucleon and Meson-Meson Interactions

abstract:
  Two-body interactions of elementary particles are useful in particle and
nuclear physics to describe qualitatively and quantitatively few- and many-body
systems. We are extending for this purpose the quantum inversion approach for
systems consisting of nucleons and mesons. From the wide range of
experimentally studied two-body systems we concentrate here on $\pi N$,
$\pi\pi$, $K^+N$, $K \pi$ and $K\bar{K}$. As input we require results of phase
shift analyses. Quantum inversion Gelfand-Levitan and Marchenko single and
coupled channel algorithms are used for Schr\"odinger type wave equations in
partial wave decomposition. The motivation of this study comes from our two
approaches: to generate and investigate potentials directly from data by means
of inversion and alternatively use linear and nonlinear boson exchange models.
The interesting results of inversion are coordinate space informations about
radial ranges, strengths, long distance behaviors, resonance characteristics,
threshold effects, scattering lengths and bound state properties.


title:
Meson-baryon coupling constants from a chiral-invariant SU(3) Lagrangian
  and application to NN scattering

abstract:
  We present a chiral-invariant meson-baryon Lagrangian which describes the
interactions of the baryon octet with the lowest-mass meson nonets. The
nonlinear realization of the chiral symmetry generates pair-meson interaction
vertices. The corresponding pair-meson coupling constants can all be expressed
in terms of the meson-nucleon-nucleon pseudovector, scalar, and vector coupling
constants, and their corresponding $F/(F+D)$ ratios, and for which empirical
estimates are given. We show that it is possible to construct an NN potential
of reasonable quality satisfying these theoretical and empirical constraints.


title: Quantum Fluctuation Effects on Nuclear Fragment Formation

abstract:
  Multifragmentation in Au+Au collisions is investigated at incident energies
in the range 100-400 MeV per nucleon by means of a recently developed quantal
Langevin model. The inclusion of quantum fluctuations enhances the average
multiplicity of intermediate mass fragments, especially in central collisions.
This is mainly because the excitation energies of fragments are reduced due to
the quantal behavior of intrinsic specific heat.


title: Fragments in Gaussian Wave-Packet Dynamics with and without correlations

abstract:
  Generalization of Gaussian trial wave functions in quantum molecular dynamics
models is introduced, which allows for long-range correlations characteristic
for composite nuclear fragments. We demonstrate a significant improvement in
the description of light fragments with correlations. Utilizing either type of
Gaussian wave functions, with or without correlations, however, we find that we
cannot describe fragment formation in a dynamic situation. Composite fragments
are only produced in simulations if they are present as clusters in the
substructure of original nuclei. The difficulty is traced to the delocalization
of wave functions during emission. Composite fragments are produced abundantly
in the Gaussian molecular dynamics in the limit $\hbar \rightarrow 0$.


title: S-wave $\pi^0$ production In pp Collision In A Covariant OBE Model

abstract:
  The total cross section for the pp to pp $\pi^0$ reaction at energies close
to threshold is calculated in a covariant one-boson-exchange model. The
amplitudes for the elementary BN to N$\pi^0$ processes are taken to be the sum
of s, u and t pole terms. The main contributions to the primary
productionamplitude is due to a sigma meson exchange. Both the scale and energy
dependence of the cross section are perfectly reproduced.