title: The lattice gas model with isospin-dependent interactions

abstract:
  In this paper we continue the investigation of the lattice gas model. The
main improvement is that we use two strengths for bonds: one between like
particles and another between unlike particle to implement the
isospin-dependence of nuclear force. The main effect is the elimination of
unphysical clusters, like the dineutron or diproton. It is therefore a better
description of nuclear system. Equation of state in mean field theory is
obtained for nuclear matter as well as for $N\ne Z$ systems. Through numerical
and analytical calculation we show that the new model maintains all the
important features of the older model. We study the effect of the Coulomb
interaction on multifragmentation of a compound system of A=86, Z=40 and also
for A=197, Z=79. For the first case the Coulomb interaction has small effect.
For the latter case the effect is much more pronounced but typical signatures
of the lattice gas model such as a minimum (maximum) in the value of $\tau$
($S_2$) are still obtained but at a much lower temperature.


title: $e^+e^-$ pairs from $\pi^-$A reactions

abstract:
  We present a dynamical study of $e^+e^-$ production in $\pi^-$A reactions at
1.3 and 1.7 GeV on the basis of the Coupled-Channel-BUU approach. The
contributions from vector mesons ($\rho,\omega$) are calculated taking into
account the collisional broadening effect and are compared to background
sources in the dilepton spectrum from the Dalitz decays of $\omega$ and $\eta$
mesons produced in the reaction. Two possible scenarios for the medium
modifications of the vector mesons are investigated, i.e. the 'dropping mass'
scheme for the $\rho$ and $\omega$ and a momentum dependent $\rho$-meson
spectral function that includes the polarization of the $\rho$-meson due to
resonant $\rho -N$ scattering.


title: Relativistic covariance of quasipotential equations

abstract:
  We argue that most of the relativistic 3-D (quasipotential) equations used in
hadron physics are inconsistent with the discrete symmetries like charge
conjugation and CPT, yielding an incorrect Lorentz structure for the calculated
Green's functions. An exception to this is the equal time approximation to the
Bethe-Salpeter equation. We present a covariant quasipotential model for the
pion-nucleon interaction based on hadronic degrees of freedom and satisfying
the full covariance.


title: Off-shell effects in dilepton production from hot interacting mesons

abstract:
  The production of dielectrons in reactions involving a_1 mesons and pions is
studied. We compare results obtained with different phenomenological
Lagrangians that have been used in connection with hadronic matter and finite
nuclei. We insist on the necessity for those interactions to satisfy known
empirical properties of the strong interaction. Large off-shell effects in
dielectron production are found and some consequences for the interpretation of
heavy ion data are outlined. We also compare with results obtained using
experimentally-extracted spectral functions.


title: Quantum-Mechanical Analysis of Single-Particle Level Density

abstract:
  A quantum-mechanical calculation of the single-particle level (s.p.l.)
density $g(\epsilon)$ is carried on by using the connection with the
single-particle Green's function. The relation between the imaginary part of
Green's function and single-particle wave functions is used separately for the
discrete and continuous states. Within the bound-states region the imaginary
part of the Green's function is calculated by using the wronskian theorem. The
Green's function corresponding to the continuum is written by using the regular
and Jost solutions of the radial Schrodinger equation. The smooth part of the
rapidly fluctuating s.p.l. density is calculated by means of the Strutinski
procedure. The continuum component of the s.p.l. density has rather close
values within either exact quantum-mechanical calculations with the Woods-Saxon
(WS) potential, or Thomas-Fermi approximation with WS as well as finite-square
potential wells, provided that the free-gas contribution is subtracted. A
similar trend is obtained by means of the simple FGM formula for the s.p.l.
density if the continuum effect is taken into account.


title:
Excitation of nuclear anharmonic vibrations in heavy-ion fusion
  reactions

abstract:
  We discuss the effects of multi-phonon excitations on heavy-ion fusion
reactions at energies near and below the Coulomb barrier, focusing especially
on the role of anharmonicities. We carry out a systematic study of those
effects on the excitation function of the fusion cross section and on the
fusion barrier distribution, by using the vibrational limit of the interacting
boson model. We also analyze the recently measured high-precision data of the
$^{16}$O + $^{148}$Sm fusion reaction with this model and discuss the
anharmonic properties of the quadrupole as well as the octupole vibrations in
$^{148}$Sm. Negative and positive static quadrupole moments are deduced for the
first 2$^+$ and 3$^-$ states in $^{148}$Sm, respectively. It is shown that the
fusion barrier distribution strongly depends on the sign of the quadrupole
moments, suggesting that subbarrier fusion reactions offer an alternative
method to extract the static quadrupole moments of phonon states in spherical
nuclei.


title:
Many Body approach to the inclusive $(e,e')$ reaction from the
  quasielastic to the $\Delta$ excitation region

abstract:
  We have performed a many body calculation of the inclusive (e,e') cross
section which runs over the three traditional regions at intermediate energies:
the quasielastic peak, the dip region and the delta region. The longitudinal
and transverse response functions in the quasielastic peak have also been
evaluated. Traditional effects like polarization, meson exchange currents,
final state interaction and delta renormalization in the nuclear medium have
been included.
  Meson exchange currents are generated from a model of pion electroproduction
on the nucleon which reproduces accurately the experimental data.
  The inclusive cross section accounts for 1N,2N,3N mechanisms of virtual
photon absorption and one pion production. Meson exchange currents associated
to the (\gamma^*,2\pi) reaction are also accounted for.
  We obtain good results for the (e,e') cross sections in the whole energy
range and for different nuclei. The response functions are also in good
agreement with the latest experimental analysis. On the other hand, the method
provides the separation of the contribution to the inclusive cross section from
different physical channels which is a necessary input to evaluate cross
sections like (e,e' N), (e,e' NN), (e,e' \pi) etc.


title: Correlations and the relativistic structure of the nucleon self-energy

abstract:
  A key point of Dirac Brueckner Hartree Fock calculations for nuclear matter
is to decompose the self energy of the nucleons into Lorentz scalar and vector
components. A new method is introduced for this decomposition. It is based on
the dependence of the single-particle energy on the small component in the
Dirac spinors used to calculate the matrix elements of the underlying NN
interaction. The resulting Dirac components of the self-energy depend on the
momentum of the nucleons. At densities around and below the nuclear matter
saturation density this momentum dependence is dominated by the non-locality of
the Brueckner G matrix. At higher densities these correlation effects are
suppressed and the momentum dependence due to the Fock exchange terms is
getting more important. Differences between symmetric nuclear matter and
neutron matter are discussed. Various versions of the Bonn potential are
considered.


title:
Effects of collective expansion on light cluster spectra in relativistic
  heavy ion collisions

abstract:
  We discuss the interplay between collective flow and density profiles,
describing light cluster production in heavy ion collisions at very high
energies. Calculations are performed within the coalescence model. We show how
collective flow can explain some qualitative features of the measured deuteron
spectra, provided a proper parametrization of the spatial dependence of the
single particle phase space distribution is chosen.


title:
Tetrahedral and Triangular Deformations of $Z=N$ Nuclei in Mass Region
  $A \sim 60-80$

abstract:
  We study static non-axial octupole deformations in proton-rich $Z=N$ nuclei,
$^{64}$Ge, $^{68}$Se, $^{72}$Kr, $^{76}$Sr, $^{80}$Zr and $^{84}$Mo, by using
the Skyrme Hartree-Fock plus BCS calculation with no restrictions on the
nuclear shape. The calculation predicts that the oblate ground state in
$^{68}$Se is extremely soft for the $Y_{33}$ triangular deformation, and that
in $^{80}$Zr the low-lying local minimum state coexisting with the prolate
ground state has the $Y_{32}$ tetrahedral deformation.


title: Bose-Einstein Correlations from Random Walk Models

abstract:
  We argue that strong final state rescattering among the secondary particles
created in relativistic heavy ion collisions is essential to understand the
measured Bose-Einstein correlations. The recently suggested ``random walk
models'' which contain only initial state scattering are unable to reproduce
the measured magnitude and K_\perp-dependence of R_\perp in Pb+Pb collisions
and the increase of R_l with increasing size of the collision system.


title: Relativistic Effects in the Electromagnetic Current at GeV Energies

abstract:
  We employ a recent approach to the non-relativistic reduction of the
electromagnetic current operator in calculations of electronuclear reactions.
In contrast to the traditional scheme, where approximations are made for the
transferred momentum, transferred energy and initial momentum of the struck
nucleon in obtaining an on-shell inspired form for the current, we treat the
problem exactly for the transferred energy and transferred momentum. We
calculate response functions for the reaction $^2H(e,e'p)n$ at CEBAF (TJNAF)
energies and find large relativistic corrections. We also show that in Plane
Wave Impulse Approximation, it is always possible to use the full operator, and
we present a comparison of such a limiting case with the results incorporating
relativistic effects to the first order in the initial momentum of the struck
nucleon.


title:
On the Evidence for Postacceleration Effects in Breakup Reactions with
  Halo Nuclei

abstract:
  We study the postacceleration of charged fragments in reactions with unstable
nuclear beams. For elastic breakup processes we show that the postaceleration
effect can be well understood in terms of closed analytical forms derived in a
quantum mechanical formulation. This gives theoretical support to the effect
experimentally observed in the breakup of Li-11 projectiles at intermediate
energies.


title: Shell Effects in Superdeformed Minima

abstract:
  Recent experimental observation of the direct links between superdeformed and
normal-deformed structures in the A~190 mass region offers a unique information
on the absolute nuclear binding energy in the 2:1 minima, and hence on the
magnitude of shell effects in the superdeformed well. In the present paper, the
self-consistent mean-field theory with density-dependent pairing interaction is
used to explain at the same time the two-particle separation energies in the
first and second wells, and the excitation energies of superdeformed states in
the A~190 and A~240 mass regions.


title:
Cooperative damping mechanism of the resonance in the nuclear
  photoabsorption

abstract:
  We propose a resonance damping mechanism to explain the disappearance of the
peaks around the position of the resonances higher than the $\Delta$ resonance
in the nuclear photoabsorption. This phenomenon is understood by taking into
account the cooperative effect of the collision broadening of $\Delta$ and
$N^{*}$, the pion distortion and the interference in the two-pion
photoproduction processes in the nuclear medium.


title:
A study of the phase transition in the usual statistical model for
  nuclear multifragmentation

abstract:
  We use a simplified model which is based on the same physics as inherent in
most statistical models for nuclear multifragmentation. The simplified model
allows exact calculations for thermodynamic properties of systems of large
number of particles. This enables us to study a phase transition in the model.
A first order phase transition can be tracked down. There are significant
differences between this phase transition and some other well-known cases.


title: Strong Coupling Improved Equilibration In High Energy Nuclear Collisions

abstract:
  In high energy nuclear collisions, most calculations on the early
equilibration of the parton plasma showed that the system does not come close
to full equilibrium, especially for the fermion components. However, since the
system is constantly evolving, the cooling effect due to expansion will lead to
a decrease of the average parton energies. So the interactions should be
enhanced by a corresponding increase of the running coupling. We show that this
leads to a faster and improved equilibration. This improvement is more
important for the fermions compensating partially for their weaker interactions
and slower equilibration.


title: Nuclear Response in Electron Scattering at High Momentum Transfer

abstract:
  The nuclear response functions for high energy electron scattering were
calculated in the wide region of excitation energy. The three typical regions
were studied: the quasi-elastic region, the $\Delta$-excitation region and the
intermediate region where the meson-exchange currents give significant
contribution. In the quasi-elastic and the $\Delta$ regions the response
functions were found for finite size nucleus with account of relativistic
kinematics. The contribution of the meson-exchange currents was calculated in
the relativistic Fermi-gas model. The results were compared with the electron
scattering data at high momentum transfer from $^{12}C$ and $^{16}O$.


title: Dynamics of a Simple Quantum System in a Complex Environment

abstract:
  We present a theory for the dynamical evolution of a quantum system coupled
to a complex many-body intrinsic system/environment. By modelling the intrinsic
many-body system with parametric random matrices, we study the types of
effective stochastic models which emerge from random matrix theory. Using the
Feynman-Vernon path integral formalism, we derive the influence functional and
obtain either analytical or numerical solutions for the time evolution of the
entire quantum system. We discuss thoroughly the structure of the solutions for
some representative cases and make connections to well known limiting results,
particularly to Brownian motion, Kramers classical limit and the
Caldeira-Leggett approach.

categories: nucl-th chao-dyn cond-mat.stat-mech nlin.CD


title: Non perturbative chiral approach to s-wave \bar{K}N interactions

abstract:
  The s-wave meson-nucleon interaction in the $S = -1$ sector is studied by
means of coupled-channel Lippmann Schwinger equations, using the lowest order
chiral Lagrangian and a cut off to regularize the loop integrals. The method
reproduces succesfully the $\Lambda (1405)$ resonance and the $K^- p \to K^- p,
\bar{K}^0 n, \pi^0 \Lambda, \pi^0 \Sigma, \pi^+ \Sigma^-, \pi^- \Sigma^+$ cross
sections at low energies. The inclusion of the $\eta \Lambda, \eta \Sigma^0$
channels in the coupled system is found very important and allows a solution in
terms of only the lowest order Lagrangian.


title: Heavy- to light-meson transition form factors

abstract:
  Semileptonic heavy -> heavy and heavy -> light meson transitions are studied
as a phenomenological application of a heavy-quark limit of Dyson-Schwinger
equations. Employing two parameters: E, the difference between the mass of the
heavy meson and the effective-mass of the heavy quark; and Lambda, the width of
the heavy-meson Bethe-Salpeter amplitude, we calculate f_+(t) for all decays on
their entire kinematically accessible t-domain. Our study favours f_B in the
range 0.135-0.17 GeV and with E=0.44 GeV and 1/Lambda = 0.14 fm we obtain
f_+^{B pi}(0) = 0.46. As a result of neglecting 1/m_c-corrections, we estimate
that our calculated values of \rho^2 = 0.87 and f_+^{DK}(0)=0.62 are too low by
approximately 15%. However, the bulk of these corrections should cancel in our
calculated values of Br(D -> \pi l nu)/Br(D -> K l nu)=0.13 and f_+^{D
pi}(0)/f_+^{DK}(0) = 1.16.


title:
The nucleon Drell-Hearn-Gerasimov sum rule within a relativistic
  constituent quark model

abstract:
  The Drell-Hearn-Gerasimov sum rule for the nucleon is investigated within a
relativistic constituent quark model formulated on the light-front. The
contribution of the N - Delta(1232) transition is explicitly evaluated using
different forms for the baryon wave functions and adopting a one-body
relativistic current for the constituent quarks. It is shown that the N -
Delta(1232) contribution to the sum rule is sharply sensitive to the
introduction of anomalous magnetic moments for the constituent quarks, at
variance with the findings of non-relativistic and relativized quark models.
The experimental value of the isovector-isovector part of the sum rule is
almost totally reproduced by the N - Delta(1232) contribution, when the values
of the quark anomalous magnetic moments are fixed by fitting the experimental
nucleon magnetic moments. Our results are almost independent of the adopted
form of the baryon wave functions and only slightly sensitive to the violation
of the angular condition caused by the use of a one-body current. The
calculated average slope of the generalized sum rule around the photon point
results to be only slightly negative at variance with recent predictions of
relativized quark models.


title: Neutron star properties with relativistic equations of state

abstract:
  We study the properties of neutron stars adopting relativistic equations of
state of neutron star matter, calculated in the framework of the relativistic
Brueckner-Hartree-Fock approximation for electrically charge neutral neutron
star matter in beta-equilibrium. For higher densities more baryons (hyperons
etc.) are included by means of the relativistic Hartree- or Hartree-Fock
approximation. The special features of the different approximations and
compositions are discussed in detail. Besides standard neutron star properties
special emphasis is put on the limiting periods of neutron stars, for which the
Kepler criterion and gravitation-reaction instabilities are considered.
Furthermore the cooling behaviour of neutron stars is investigated, too. For
comparison we give also the outcome for some nonrelativistic equations of
state.


title: Hard Probes in High-energy Heavy-ion Collisions

abstract:
  Hard QCD processes in ultrarelativistic heavy-ion collisions become
increasingly relevant and they can be used as probes of the dense matter formed
during the violent scatterings. We will discuss how one can use these hard
probes to study the properties of the dense matter and the associated
phenomenologies. In particular, we study the effect of jet quenching due to
medium-induced energy loss on inclusive particle $p_T$ distributions and
investigate how one can improve the measurement of parton energy loss in direct
photon events


title: Shell-model calculations for the three-nucleon system

abstract:
  We use Faddeev's decomposition to solve the shell-model problem for three
nucleons. The dependence on harmonic-oscillator excitations allowed in the
model space, up to $32 \hbar\Omega$ in the present calculations, and on the
harmonic-oscillator frequency is studied. Effective interactions derived from
Nijmegen II and Reid93 potentials are used in the calculations. The binding
energies obtained are close to those calculated by other methods. The structure
of the Faddeev equations is discussed and a simple formula for matrix elements
of the permutation operators in a harmonic-oscillator basis is given. The Pauli
principle is properly treated in the calculations.


title: A clue to the mechanism of $\Lambda K^+$ production in $pp$-reactions

abstract:
  We analyse the $p p \to p \Lambda K^+$ total cross section data which were
recently measured by the COSY-11 collaboration at an energy 2~MeV above the
reaction threshold. Our analysis suggests that the measurement of the invariant
mass spectrum for the $\Lambda K^+$ at energies around 100 MeV above the
threshold can provide a new constraint on the theoretical calculations for this
reaction. In particular, the measurement can give a clue as to whether the
reaction is dominated by resonance excitation or not. Thus, it should
contribute to further understanding of the strangeness production mechanism. We
show the invariant mass spectra for the $\Lambda K^+$ system in these optimal
kinematic conditions calculated by several approaches, and demonstrate that our
suggestion is experimentally feasible.


title: The role of tensor force in nuclear matter saturation

abstract:
  Using a relativistic Dirac-Brueckner analysis the pion contribution to the
ground state energy of nuclear matter is studied. Evidence is presented that
the role of the tensor force in the saturation mechanism is substantially
reduced compared to its dominant role in a usual non-relativistic treatment.
The reduction of the pion contribution in nuclear matter is due to many-body
effects present in a relativistic treatment. In particular, we show that the
damping of OPEP is actually due to the decrease of $M^*/M$ with increasing
density.


title:
Nuclear multifragmentation induced by electromagnetic fields of
  ultrarelativistic heavy ions

abstract:
  We study the disintegration of nuclei by strong electromagnetic fields
induced by ultrarelativistic heavy ions. The proposed multi-step model includes
1) the absorption of a virtual photon by a nucleus, 2) intranuclear cascades of
produced hadrons and 3) statistical decay of the excited residual nucleus. The
combined model describes well existing data on projectile fragmentation at
energy 200 GeV per nucleon. Electromagnetic multifragmentation of nuclei is
predicted to be an important reaction mechanism at RHIC and LHC energies.


title: Effect of $\rho N$ channel in the $\gamma N \to \pi \pi N$ reactions

abstract:
  A model for the two-pion photoproduction on the nucleon proposedearlier is
modified to simultaneously explain the total cross sections and the invariant
mass spectra. Using this model, we discuss the role of the $\rho $ meson in the
$\gamma N \to \pi \pi N$ reaction.


title:
Are we close to the QGP? - Hadrochemical vs. microscopic analysis of
  particle production in ultrarelativistic heavy ion collisions

abstract:
  Ratios of hadronic abundances are analyzed for pp and nucleus-nucleus
collisions at sqrt(s)=20 GeV using the microscopic transport model UrQMD.
Secondary interactions significantly change the primordial hadronic cocktail of
the system. A comparison to data shows a strong dependence on rapidity. Without
assuming thermal and chemical equilibrium, predicted hadron yields and ratios
agree with many of the data, the few observed discrepancies are discussed.


title:
Screening effects on the elastic nucleon-nucleon cross section in
  relativistic nuclear matter

abstract:
  We investigate the screening effects on the nucleon-nucleon elastic cross
section inside nuclear matter at zero and finite temperature. The N-N
interaction is described phenomenologically via meson exchanges ($\sigma$,
$\pi$ and $\omega$) in the framework of a relativistic lagrangian model. The
expressions for the in-medium meson propagators, which take into account the
effects of matter polarization and renormalized vacuum polarization, are used
in the calculation of the various meson contributions to the total cross
section in the one-boson exchange approximation. The final expressions allow a
satisfactory fit of the Coulomb substracted proton-proton cross section data in
vacuum. At finite density or temperature the cross section is reduced as
compared to the vacuum values and compatible with the existing experimental
constraints. At high density the $p$-$p$ differential cross section gets
increasingly forward and backward peaked. The $\sigma$-$\omega$ mixing plays a
key role in the understanding of the results.


title:
Improved $d$+$^4$He potentials by inversion, the tensor force and
  validity of the double folding model

abstract:
  Improved potential solutions are presented for the inverse scattering problem
for $d$+$^4$He data. The input for the inversions includes both the data of
recent phase shift analyses and phase shifts from RGM coupled-channel
calculations based on the NN Minnesota force. The combined calculations provide
a more reliable estimate of the odd-even splitting of the potentials than
previously found, suggesting a rather moderate role for this splitting in
deuteron-nucleus scattering generally. The approximate parity-independence of
the deuteron optical potentials is shown to arise from the nontrivial
interference between antisymmetrization and channel coupling to the deuteron
breakup channels. A further comparison of the empirical potentials established
here and the double folding potential derived from the M3Y effective NN force
(with the appropriate normalisation factor) reveals strong similarities. This
result supports the application of the double folding model, combined with a
small Majorana component, to the description even of such a loosely bound
projectile as the deuteron. In turn, support is given for the application of
iterative-perturbative inversion in combination with the double folding model
to study fine details of the nucleus-nucleus potential. A $d$-$^4$He tensor
potential is also derived to reproduce correctly the negative $^6$Li quadrupole
moment and the D-state asymptotic constant.


title: Double $\Lambda$ and the $\Lambda-\Lambda$ Interaction

abstract:
  The $\Lambda$-$\Lambda$ effective interaction, in the channel $L=S=0$, in the
nuclear medium is fitted to the available binding energies,
$B_{\Lambda\Lambda}$, of double $\Lambda$ hypernuclei:
$^{6}_{\Lambda\Lambda}$He, $^{10}_{\Lambda\Lambda}$Be and
$^{13}_{\Lambda\Lambda}$B. The mesonic decay of these hypernuclei is also
investigated. Finally, this effective interaction is used to predict the
binding energies and mesonic decays widths of heavier double $\Lambda$
hypernuclei.


title:
Nucleon Charge Symmetry Breaking and Parity Violating Electron-Proton
  Scattering

abstract:
  The consequences of the charge symmetry breaking effects of the mass
difference between the up and down quarks and electromagnetic effects for
searches for strangeness form factors in parity violating electron scattering
from the proton are investigated. The formalism necessary to identify and
compute the relevant observables is developed by separating the Hamiltonian
into charge symmetry conserving and breaking terms. Using a set of SU(6)
non-relativistic quark models, the effects of the charge symmetry breaking
Hamiltonian are considered for experimentally relevant alues of the momentum
transfer and found to be less than about 1 percent. The charge symmetry
breaking corrections to the Bjorken sum rule are also studied and shown to
vanish in first-order perturbation theory.


title: Towards exotic nuclei via binary reaction mechanism

abstract:
  Assuming a binary reaction mechanism, the yield of isotopes near the heaviest
$N=Z$ neutron-deficit nucleus $^{100}$Sn is studied with a microscopic
transport model. The large influence of nuclear shell structure and isotope
composition of the colliding nuclei on the production of exotic nuclei is
demonstrated. It is shown that the reaction $^{54}$Fe+$^{106}$Cd seems to be
most favourable for producing primary exotic Sn isotopes which may survive if
the excitation energy in the entrance reaction channel is less than about 100
MeV. In the case of large differences in the charge (mass) numbers between
entrance and exit channels the light fragment yield is essentially fed from the
decay of excited primary heavier fragments. The existence of optimal energies
for the production of some oxygen isotopes in the binary mechanism is
demonstrated for the $^{32}$S+$^{197}$Au reaction.


title:
Light Nuclei near Neutron and Proton Drip Lines in the Relativistic
  Mean-Field Theory

abstract:
  We have made a detailed study of the ground-state properties of nuclei in the
light mass region with atomic numbers Z=10-22 in the framework of the
relativistic mean-field (RMF) theory. The nonlinear $\sigma\omega$ model with
scalar self-interaction has been employed. The RMF calculations have been
performed in an axially deformed configuration using the force NL-SH. We have
considered nuclei about the stability line as well as those close to proton and
neutron drip lines. It is shown that the RMF results provide a good agreement
with the available empirical data. The RMF predictions also show a reasonably
good agreement with those of the mass models. It is observed that nuclei in
this mass region are found to possess strong deformations and exhibit shape
changes all along the isotopic chains. The phenomenon of the shape coexistence
is found to persist near the stability line as well as near the drip lines. It
is shown that the magic number N=28 is quenched strongly, thus enabling the
corresponding nuclei to assume strong deformations. Nuclei near the neutron and
proton drip lines in this region are also shown to be strongly deformed.


title: Collective flow in central Au-Au collisions at 150, 250 and 400 A MeV

abstract:
  Radial collective flow and thermalization are studied in gold on gold
collisions at 150, 250 and 400 A MeV bombarding energies with a
relativistically covariant formulation of a QMD code. We find that radial flow
and "thermal" energies calculated for all the charged fragments agree
reasonably with the experimental values. The experimental hardware filter at
small angles used in the FOPI experiments at higher energies selects mainly the
thermalized particles.


title:
Barrier and internal wave contributions to the quantum probability
  density and flux in light heavy-ion elastic scattering

abstract:
  We investigate the properties of the optical model wave function for light
heavy-ion systems where absorption is incomplete, such as $\alpha + ^{40}$Ca
and $\alpha + ^{16}$O around 30 MeV incident energy. Strong focusing effects
are predicted to occur well inside the nucleus, where the probability density
can reach values much higher than that of the incident wave. This focusing is
shown to be correlated with the presence at back angles of a strong enhancement
in the elastic cross section, the so-called ALAS (anomalous large angle
scattering) phenomenon; this is substantiated by calculations of the quantum
probability flux and of classical trajectories. To clarify this mechanism, we
decompose the scattering wave function and the associated probability flux into
their barrier and internal wave contributions within a fully quantal
calculation. Finally, a calculation of the divergence of the quantum flux shows
that when absorption is incomplete, the focal region gives a sizeable
contribution to nonelastic processes.


title: Relativistic deuteron structure function at large Q^2

abstract:
  The deuteron deep inelastic unpolarized structure function F_2^D is
calculated using the Wilson operator product expansion method. The long
distance behaviour, related to the deuteron bound state properties, is
evaluated using the Bethe-Salpeter equation with one particle on mass shell.
The calculation of the ratio F_2^D/F_2^N is compared with other convolution
models showing important deviations in the region of large x. The implications
in the evaluation of the neutron structure function from combined data on
deuterons and protons are discussed.


title:
The Equation of State of Nuclear Matter in Heavy Ion Collisions at
  CERN-SPS Energies from the Viewpoint of Relativistic Hydrodynamics

abstract:
  We present refits of single inclusive cross section data of mesons and
baryons for central 158 $AGeV$ Pb+Pb collisions measured by the NA44 and NA49
Collaborations. In the theoretical approach we use the relativistic
hydrodynamical code HYLANDER-C. We investigate several equations of state in
their capability to describe the measured single inclusive momentum
distributions. Based on the obtained fits we present results of the calculated
Bose-Einstein correlation functions of identical pion pairs and discuss their
features in comparison to measurements.


title: Moscow-type NN-potentials and three-nucleon bound states

abstract:
  A detailed description of Moscow-type (M-type) potential models for the NN
interaction is given. The microscopic foundation of these models, which appear
as a consequence of the composite quark structure of nucleons, is discussed.
M-type models are shown to arise naturally in a coupled channel approach when
compound or bag-like six-quark states, strongly coupled to the NN channel, are
eliminated from the complete multiquark wave function. The role of the
deep-lying bound states that appear in these models is elucidated. By
introducing additional conditions of orthogonality to these compound six-quark
states, a continuous series of almost on-shell equivalent nonlocal interaction
models, characterized by a strong reduction or full absence of a local
repulsive core (M-type models), is generated. The predictions of these
interaction models for 3N systems are analyzed in detail. It is shown that
M-type models give, under certain conditions, a stronger binding of the 3N
system than the original phase-equivalent model with nodeless wave functions.
An analysis of the 3N system with the new versions of the Moscow NN potential
describing also the higher even partial waves is presented. Large deviations
from conventional NN force models are found for the momentum distribution in
the high momentum region. In particular, the Coulomb displacement energy for
nuclei ^3He - ^3H displays a promising agreement with experiment when the ^3H
binding energy is extrapolated to the experimental value.


title: Strangelets and Strange Quark Matter

abstract:
  The properties of finite lumps of strange quark matter (strangelets) with
emphasis on the two scenarios of producing strange matter in relativistic heavy
ion collisions are summarized. As an outlook, the possibility of short-lived
strange composites and charmed matter are discussed for coming heavy ion
experiments.


title:
Approximate Treatment of Lepton Distortion in Charged-Current Neutrino
  Scattering from Nuclei

abstract:
  The partial-wave expansion used to treat the distortion of scattered
electrons by the nuclear Coulomb field is simpler and considerably less
time-consuming when applied to the production of muons and electrons by low and
intermediate-energy neutrinos. For angle-integrated cross sections, however, a
modification of the "effective-momentum-transfer" approximation seems to work
so well that for muons the full distorted-wave treatment is usually
unnecessary, even at kinetic energies as low as an MeV and in nuclei as heavy
as lead. The method does not work as well for electron production at low
energies, but there a Fermi function usually proves adequate. Scattering of
electron-neutrinos from muon decay on iodine and of atmospheric neutrinos on
iron are discussed in light of these results.


title: Nucleon-Nucleon Interactions and Observables

abstract:
  A class of nucleon-nucleon interactions which are exactly phase equivalent to
a given realistic nucleon-nucleon interaction are exhibited. These interaction
have the property that the RMS radius of the deuteron can be made arbitrarily
large without changing any of the scattering or bound-state observables. With
this construction it is possible to find realistic interactions that do not
obey the linear relation between the RMS radius and the triplet scattering
length observed by Klarsfeld et. al. The interpretation of these examples is
discussed.


title: Field theoretic study of light hypernuclei

abstract:
  A nonperturbative field theoretic calculation has been made for the $s$-shell
hypernuclei. Here we dress the $\Lambda$- and $\Sigma$- hypernuclei with
off-mass shell pion pairs. The analysis replaces the scalar isoscalar potential
by quantum coherent states. The binding energies of $^{4+n\Lambda}$He
$(n=0,1,2)$ agree quite well with the RMF result of Greiner. The experimental
binding energies of $^4$He and $^3$He are reasonably well reproduced in our
calculation. A satisfactory description of the relevant experimental $\Lambda$-
and $\Sigma$- separation energies has been obtained.


title: K0-Sigma+ Photoproduction with SAPHIR

abstract:
  Preliminary results of the analysis of the reaction p(gamma,K0)Sigma+ are
presented. We show the first measurement of the differential cross section and
much improved data for the total cross section than previous data. The data are
compared with model predictions from different isobar and quark models that
give a good description of p(gamma,K+)Lambda and p(gamma,K+)Sigma0 data in the
same energy range. Results of ChPT describe the data adequately at threshold
while isobar models that include hadronic form factors reproduce the data at
intermediate energies.


title:
$\pi^+$ Emission from Hypernuclei and the Weak $\Delta I=3/2$
  Transitions

abstract:
  Low energy $\pi^+$ emission in hypernuclear weak decays is studied in the
soft pion limit. It is found that the $\pi^+$ decay amplitude is dominated by
the $\Delta I=3/2$ part of nonmesonic weak decays according to the soft pion
theorem. The ratios, $R(\pi^+/soft \pi^-) $, for light hypernuclei are
estimated in the direct quark mechanism, which predicts violation of the
$\Delta I=1/2$ rule, and found to be about 1/3 for $^4_{\Lambda}He$.


title:
A Study of the Coulomb Dissociation of 8B and the 7Be(p, gamma)8B
  Reaction

abstract:
  We study the breakup reactions of 8B projectiles in high energy (50 and 250
MeV/u) collisions with heavy nuclear targets (208Pb). The intrinsic nuclear
wave functions are calculated using a simple model, as well as a simple optical
potential. We demonstrate that nuclear effects are negligible and evaluate the
contributions of various (E1, E2 and M1) multipolarities. A good agreement with
measured data is obtained with insignificant M1 contribution (at 50 MeV/u) and
very small E2 contribution.


title: Density Fluctuations in the Quark-Gluon Plasma

abstract:
  Using the kinetic theory we discuss how the particle and energy densities of
the quark-gluon plasma fluctuate in a space-time cell. The fluctuations in the
equilibrium plasma and in that one from the early stage of ultrarelativistic
heavy-ion collisions are estimated. Within the physically interesting values of
the parameters involved the fluctuations appear sizeable in both cases.


title: Delta excitation in K^+-nucleus collisions

abstract:
  We present calculations for \Delta excitation in the (K^+,K^+) reaction in
nuclei. The background from quasielastic K^+ scattering in the \Delta region is
also evaluated and shown to be quite small in some kinematical regions, so as
to allow for a clean identification of the \Delta excitation strength. Nuclear
effects tied to the \Delta renormalization in the nucleus are considered and
the reaction is shown to provide new elements to enrich our knowledge of the
\Delta properties in a nuclear medium.


title: Chiral Perturbation Theory and Nuclear Physics

abstract:
  Chiral symmetry serves as a guiding principle in low-energy hadron dynamics.
An effective lagrangian, which explicitly breaks chiral symmetry via a small
mass term, allows for a systematic method of calculating higher order
corrections to tree-level results. This is applied to radiative muon capture on
hydrogen, %to extract the weak pseudoscalar form factor, and to proton-proton
$\pi^0$ production near threshold. Both processes pose theoretical challenges
in light of recent experimental results.


title: The $\pi^+$--emission puzzle in $^4_\Lambda$He decay

abstract:
  We re-examine the puzzling $\pi^+$ emission from the weak decay of
$^4_\Lambda$He and propose an explanation in terms of a three-body decay of the
virtual $\Sigma^+$. Such a resolution of the $\pi^+$ decay puzzle is consistent
with the calculated $\Sigma^+$ probability in light $\Lambda$ hypernuclei as
well as the experimentally observed $\pi^+$ energy spectrum and $s$--wave
angular distribution.


title:
Chemical freezeout in relativistic A+A collisions: is it close to the
  QGP?

abstract:
  Preliminary experimental data for particle number ratios in the collisions of
Au+Au at the BNL AGS (11$A$ GeV/$c$) and Pb+Pb at the CERN SPS (160$A$ GeV/$c$)
are analyzed in a thermodynamically consistent hadron gas model with excluded
volume. Large values of temperature, T=140--185 MeV, and baryonic chemical
potential, $\mu_b=590$--270 MeV, close to the boundary of the quark-gluon
plasma phase are found from fitting the data. This seems to indicate that the
energy density at the chemical freezeout is tremendous which would be indeed
the case for the point-like hadrons. However, a self-consistent treatment of
the van der Waals excluded volume reveals much smaller energy densities which
are very far below a lowest limit estimate of the quark-gluon plasma energy
density.


title:
Existence and transitions properties of three-deuteron muonic molecule
  (3d 2e^- \mu^-)

abstract:
  We calculated the energy and the size of the three-deuteron muonic molecule
(3d 2e^- \mu^-) = D_3 \mu. It turns out that this system possesses two
equilibrium positions, one at distances typical for muonic molecules and a
second one at the usual molecular size. We show, moreover, that the fusion
probability of the three deuterons is considerably enhanced due to the
existence of a ^6Li^* threshold resonance. Our estimates indicate that this
probability is considerably higher than the decay rate of the competing Auger
transition.


title: Multiphonon Giant Resonances

abstract:
  A new class of giant resonances in nuclei is discussed, i.e., giant
resonances built on other giant resonances. These resonances are observed with
very large cross sections in relativistic heavy ion collisions. A great
experimental and theoretical effort is underway to understand the reaction
mechanism which leads to the excitation of these states in nuclei, as well as
the better microscopic understanding of their properties, e.g., strength,
energy centroids, widths, and anharmonicities.


title:
Information entropy as a measure of the quality of a nuclear density
  distribution

abstract:
  The information entropy of a nuclear density distribution is calculated for a
number of nuclei. Various phenomenological models for the density distribution
using different geometry are employed. Nuclear densities calculated within
various microscopic mean field approaches are also employed. It turns out that
the entropy increases on going from crude phenomenological models to more
sophisticated (microscopic) ones. It is concluded that the larger the
information entropy, the better the quality of the nuclear density
distribution. An alternative approach is also examined: the net information
content i.e. the sum of information entropies in position and momentum space
$S_{r}+S_{k}$. It is indicated that $S_{r}+S_{k}$ is a maximum, when the best
fit to experimental data of the density and momentum distributions is attained.


title: Radiative Energy-Loss of Heavy Quarks in a Quark-Gluon Plasma

abstract:
  We estimate the radiative energy-loss of heavy quarks, produced from the
initial fusion of partons, while propagating in a quark-gluon plasma which may
be formed in the wake of relativistic heavy ion collisions. We find that the
radiative energy-loss for heavy quarks is larger than the collisional
energy-loss for all energies. We point out the consequences on possible signals
of the quark-gluon plasma.


title: Two-Neutrino Double Beta Decay: Critical Analysis

abstract:
  We have performed a critical analysis of different approximation schemes for
the calculation of two-neutrino double beta decay (TNDBD) matrix elements. We
have shown that within the single-particle approximation of nuclear Hamiltonian
the TNDBD matrix element is equal to zero. The (renormalized) quasiboson
approximation scheme imply for TNDBD transition operator to be a constant, if
one requires the equivalence of initial and final (renormalized) QRPA
Hamiltonians. It means that TNDBD is a higher order process in the boson
expansion of the nuclear Hamiltonian. We have found that the mismatching of
both Hamiltonians is getting worse with increasing strength of particle-
particle interaction especially in the case of QRPA Hamiltonians. It is
supposed to be one of the reasons of the extreme sensitivity of studied matrix
element to the residual interaction appearing in explicit calculations
involving the intermediate nucleus. Further, the Operator Expansion Method
(OEM) has been reconsidered and new transition operators have been rederived in
a consistent way. The validity of the OEM approximation has been discussed in
respect to the other approximation schemes. The OEM combined with QRPA or RQRPA
ground state wave functions reflects sensitively the instabilities incorporated
in the considered ground states. Therefore, the predicting power of the OEM
should be studied with help of other ground state wave functions. e.g. shell
model ones.


title:
Vector Meson Photoproduction with an Effective Lagrangian in the Quark
  Model I: Formalism

abstract:
  A quark model approach to the photoproduction of vector mesons off nucleons
is proposed. Its starting point is an effective Lagrangian of the interaction
between the vector meson and the quarks inside the baryon. This paper develops
the formalism and highlights the dynamical roles of s-channel resonances. It is
demonstrated that the proposed approach is ideal to support searching for the
missing resonances in the vector meson photoproduction experiments proposed at
TJNAF.


title:
Excluded volume hadron gas model for particle number ratios in A+A
  collisions

abstract:
  We recapitulate a thermodynamically consistent excluded volume hadron gas
model and examine its differences with other ``thermal models'' used in the
literature. Preliminary experimental data for particle number ratios in the
collisions of Au+Au at the BNL AGS (11$A$ GeV/$c$) and Pb+Pb at the CERN SPS
(160$A$ GeV/$c$) are analyzed. For equal values of the hadron hard-core
parameters the excluded volume model gives essentially the ideal gas
predictions for the particle number ratios, which is similar to other thermal
models. We observe, however, the systematic excess of experimental pion
abundances compared to the ideal gas results. This effect can be explained in
our model by a smaller pion hard-core volume compared to those of other
hadrons. The absolute values for particle number and energy densities at the
chemical freezeout are predicted with a simultaneous fit to all these AGS and
SPS particle number ratios.


title:
Quantum fluctuation effects on hyperfragment formation from Xi^-
  absorption at rest on 12C

abstract:
  Formation mechanisms of single, twin, and double hypernuclei from Xi^-
absorption at rest on 12C are investigated with an refined microscopic
transport model, that incorporates the recently developed Quantal Langevin
treatment into Antisymmetrized Molecular Dynamics. The quantum fluctuations
suppress the formation probability of double hyperfragments to around 10%,
which is comparable to the experimental data, and the dynamical formation of
twin hyperfragment can be described qualitatively.


title: Coulomb Effects on Particle Spectra in Relativistic Nuclear Collisions

abstract:
  Coulomb effects on $\pi^\pm$ and $K^\pm$ spectra in relativistic nuclear
collisions are investigated. At collision energies around 1 GeV the ratio of
$\pi^-$ to $\pi^+$ is enhanced several times at low transverse momenta but less
at ultrarelativistic energies. We describe the ratios at SIS, AGS and SPS
energies with simple analytic models as well as more elaborate numerical models
incorporating the expansion dynamics. The Coulomb effect depends on the
properties of the source after the violent collision phase and provides
information on source sizes, freeze-out times, and expansion velocities.
Comparison with results from HBT analyses are made. Predictions for $\pi^\pm$
and $K^\pm$ at RHIC and LHC energies are given.


title: The quark condensate in relativistic nucleus-nucleus collisions

abstract:
  We compute the modification of the quark condensate $<\bar{q} q>$ in
relativistic nucleus-nucleus collisions and estimate the 4-volume, where the
quark condensate is small ($<\bar{q}q>/<\bar{q} q>_0\leq$ 0.1--0.3) using
hadron phase-space distributions obtained with the quark-gluon string model. As
a function of the beam energy the 4-volume rises sharply at a beam energy
$E_{lab}/A \simeq$ (2--5) GeV, remains roughly constant up to beam energies
$\simeq 20$ GeV and rises at higher energies. At low energies the reduction of
the condensate is mainly due to baryons, while at higher energies the rise of
the 4-volume is due to the abundant mesons produced. Based on our results we
expect that moderate beam energies on the order of 10 GeV per nucleon are
favourable for studying the restoration of chiral symmetry in a baryon-rich
environment in nucleus-nucleus collisions.


title:
Thermal Model Analysis of Particle Ratios at GSI Ni-Ni Experiments Using
  Exact Strangeness Conservation

abstract:
  The production of hadrons in Ni-Ni at the GSI is considered in a hadronic gas
model with chemical equilibrium. Special attention is given to the abundance of
strange particles which are treated using the exact conservation of
strangeness. It is found that all the data can be described using a temperature
T = 70 pm 10 MeV and a baryon chemical potential mu_B = 720 pm 20 MeV.


title: Quasielastic K+ scattering in nuclei

abstract:
  The quasielastic scattering kaon-nucleus experiment performed at BNL is
analyzed in a finite nucleus continuum random phase approximation framework,
treating the reaction mechanism in Glauber theory up to two-step inelastic
processes. A good description of the data is achieved, also providing a useful
constraint on the strength of the effective particle-hole interaction in the
scalar-isoscalar channel at intermediate momentum transfers.


title:
Off-Shell Structures of Nucleon-Nucleon t-matrices and their Influence
  on Nucleon-Nucleus Elastic Scattering Observables

abstract:
  The sensitivity of nucleon-nucleus elastic scattering observables to the
off-shell structure of nucleon-nucleon t-matrices, derived from realistic NN
potentials, is investigated within the context of a full-folding model based on
the impulse approximation. Our study uses recently developed NN potential
models, which describe a subset of the NN data base with a $\chi^2$ per datum
$\sim$1, which means that the NN t-matrices are essentially on-shell
equivalent. We calculate proton-nucleus elastic scattering observables for
$^{16}$O, $^{40}$Ca, and $^{208}$Pb between 100 and 200 MeV laboratory energy.
We find that the elastic scattering observables are insensitive to off-shell
differences of the employed NN t-matrices. A more detailed investigation of the
scattering equation and the optical potential as given in a factorized
approximation reveals that the elastic scattering observables do not sample the
NN t-matrices very far off-shell where they exhibit differences.


title:
Asymmetric semi-infinite nuclear matter: surface and curvature
  properties in relativistic and non-relativistic models

abstract:
  Surface and curvature properties of asymmetric nuclear matter are studied
beyond the proton drip. Using the semiclassical extended Thomas-Fermi method,
the calculations are performed in the non-relativistic and relativistic meson
field theories (Skyrme forces and non linear sigma-omega parametrizations).
First we discuss the bulk equilibrium between the nuclear and drip phases. Next
we analyze the asymmetric surface as a function of the bulk neutron excess. We
examine local quantities related to the density profiles and, for two
definitions of the bulk reference energy, the surface and curvature energy
coefficients. The calculation of the curvature energy is carefully treated. The
sensitivity of the nuclear surface to the relativistic effects is investigated.
Mass formulae useful for arbitray neutron excess are discussed, and their limit
at small asymmetries is compared with the liquid droplet model mass formula.


title: Lambda(1405) as a multiquark state

abstract:
  In the QCD sum rule approach we predict the $\Lambda$ (1405) mass by choosing
the $\pi^0\Sigma^0$ multiquark interpolating field. It is found that the mass
is about 1.419 GeV from $\Pi_1 (q^2)$ sum rule which is more reliable than
$\Pi_q (q^2)$ sum rule, where $\Pi_q (q^2)$ and $\Pi_1 (q^2)$ are two invariant
functions of the correlator $\Pi (q^2)$. We also present the sum rules for the
$K^+ p$ and the $\pi^+\Sigma^+$ multiquark states, and compare to those for the
$\pi^0\Sigma^0$ multiquark state. The mass of the $\Lambda$ (1600) can be also
reproduced in our approach.


title:
The $\Xi^- +d\to n+\Lambda+\Lambda$ reaction as a probe of the
  $\Lambda\Lambda$ interaction

abstract:
  Within the framework of the Faddeev equations we demonstrate that a
$\Lambda\Lambda-\Xi N$ interaction that gives a $\Lambda\Lambda$ scattering
length comparable to the $nn$ scattering length, and the binding energy of $^{\
  6}_{\Lambda\Lambda}$He as an $\alpha\Lambda\Lambda-\alpha\Xi N$ system,
produces a final state interaction peak in the neutron spectrum for the
reaction $\Xi^- d \to n\Lambda\Lambda$. This suggests that this reaction could
be used to constrain the $\Lambda\Lambda$ scattering length.


title: Mesonic and Binding Contributions to the Nuclear Drell-Yan Process

abstract:
  We have evaluated the Drell-Yan cross section in nuclei paying special
attention to the meson cloud contribution from pion and rho-meson, for which an
accurate calculation using the meson nuclear spectral functions is used.
Similarly, the nucleonic contribution is evaluated in terms of a relativistic
nucleon spectral function. Fair agreement with experiment is found for
different nuclei and the results show a sizeable contribution from the
renormalized meson cloud. In order to reproduce the experiment a novel element
is introduced, consisting of a gradual energy loss of the incoming proton in
its pass through the nucleus which produces a strong A dependence at x_1 large.


title: Photon Rates for Heavy-Ion Collisions from Hidden Local Symmetry

abstract:
  We study photon production from the hidden local symmetry approach that
includes pions, rho and a1 mesons and compute the corresponding photon emission
rates from a hadronic gas in thermal equilibrium. Together with experimental
radiative decay widths of the background, these rates are used in a
relativistic transport model to calculate single photon spectra in heavy-ion
collisions at SPS energies. We then employ this effective theory to test three
scenarios for the chiral phase transition in high-temperature nuclear matter
including decreasing vector meson masses. Although all calculations respect the
upper bound set by the WA80 Collaboration, we find the scenarios could be
distinguished with more detailed data.


title: Photons from Hadronic Matter at Finite Temperature

abstract:
  Temperature dependence of hadronic decay widths and masses are studied within
the framework of an effective Lagrangian approach. At finite temperature the
hadronic masses do not seem to follow a universal scaling law. Considering an
exhaustive set of hadronic reactions and vector meson decays we have estimated
the photon spectrum emitted from hot hadronic matter taking into account medium
effects through thermal loop corrections on the hadronic decay widths and
masses. An enhancement in photon emission rate is obtained when we use the
in-medium masses of vector mesons in our calculations. It is observed that the
effect of $\rho$ decay width on the photon spectra is negligible.


title:
An efficient projection algorithm and its application to the spurious
  center-of-mass motion problem

abstract:
  Based on the correspondence of projection to an eigenvalue problem via the
underlying group structure, we generalize the projection algorithm proposed by
Morrison et al. This algorithm is eligible for large-scale computations,
because we can avoid the accumulation of errors. As an example, we apply it to
the spurious c.m. motion in a multi-$\hbar\omega$ shell-model calculation. In
comparison with Lawson's method, the present method is exact and nevertheless
does not need longer CPU time. It is pointed out that the exact treatment of
the spurious c.m. motion is crucial to some physical quantities.


title: $\rho$-Meson Production and Decay in Proton-Nucleus Collisions

abstract:
  We analyze the production of $\rho$-mesons in $p + A$ reactions including
both the production by proton-nucleon as well as pion-nucleon collisions within
a coupled channel transport approach. The final state interactions of the
$\rho$-meson with nucleons are evaluated from a resonance model which allows to
extract elastic and inelastic cross sections. We include the latter final state
interactions, the $\rho$-meson decay into two pions as well as the final
pion-nucleon interactions within the transport approach. We find the invariant
mass distribution of pion pairs to be sensitive to the $\rho$-meson properties
in the nuclear medium. However, due to the strong final state interactions of
pions only light targets like $^{12}C$ might be suited to extract a
$\rho$-signal from the uncorrelated two pion background which carries
information about the in-medium properties of the $\rho$-meson.


title: Caloric curve in Au + Au collisions

abstract:
  Realistic caloric curves are obtained for $^{197}Au + ^{197}Au$ reaction with
incident energy ranging from 35 to 130 MeV/nucleon in the dynamic statistical
multifragmentation model. It is shown that for excitation energy 3 to 8
MeV/nucleon, the temperature remains constant in the range 5 to 6 MeV, which is
close to experiment. The mechanism of energy deposition through the
tripartition of colliding system envisaged in this model together with
inter-fragment nuclear interaction are found to play important role. A possible
signature of liquid-gas phase transition is seen in the specific heat
distribution calculated from these caloric curves, and the critical temperature
is found to be $\sim$ 6 to 6.5 MeV.


title:
Frozen motion model and dilepton production from 200A GeV S+W collisions
  at CERN SPS

abstract:
  We have analysed the invariant mass distribution of dileptons in S+W
collisions at 200A GeV as measured by the HELIOS-3 collaboration at CERN SPS.
Three scenarios were considered where the collision lead to formation of (i)
the quark-gluon plasma, (ii) the ideal hot hadron gas and (iii) the viscous hot
hadron gas. The space-time evolution was governed by the minimal extension of
the Bjorken hydrodynamics. All the three scenarios indicate excess dileptons in
the experiment.


title: Kaon and Hyperon Form Factors in Kaon Electroproduction on the Nucleon

abstract:
  The electromagnetic form factors of strange mesons and baryons are studied by
means of kaon electroproduction on the nucleon. The response functions that are
sensitive to the K0, Lambda, Sigma, and KK*\gamma transition form factors are
systematically explored. The effects of these form factors on several response
functions are discussed.


abstract:
  This is the summary of the working group on Hadron Polarizabilities and Form
Factors of the Chiral Dynamics Workshop in Mainz, September 1-5, 1997.


title:
Effect of colour singletness of quark-gluon plasma in quark-hadron phase
  transition

abstract:
  Consequences of the constraint of SU(3) colour singletness of quark-gluon
plasma are studied. This restriction increases the free energy barrier for the
formation of hadronic bubble in supercooled phase and influences significantly
the dynamics of the initial stage of quark-hadron phase transition. It also
introduces terms dependent on the volume occupied by the plasma in the energy
density and the pressure. These modifactions vanish in the limit of an infinite
volume. The last stage of the hadronization of the QGP likely to be formed in
relativistic heavy ion collisions is necessarily characterized by a decreasing
volume containing the quark matter, and thus these corrections become
important. The nucleation of plasma droplets at AGS energies is also seen to be
strongly affected by the requirement of colour singletness, and the choice of
prefactor.


title: Lipkin-Meshkov-Glick model at finite temperature

abstract:
  The Lipkin-Meshkov-Glick model is used to examine the validity of some
approximate methods in a many-body theory at finite temperatures. Namely, the
thermal random phase approximation (TRPA) and the thermal renormalized random
phase approximation (TRRPA) are studied. An average energy of the system, an
average quasispin projection and a particle number variance are calculated
within these approximation and exactly with the grand canonical ensemble
partition function. On the whole the results of TRRPA are found to be in better
agreement with the exact ones. The validity of the both approximation becomes
better with increasing temperature as well as particle number.


title: Muon number violating processes in nuclei

abstract:
  The flavour violating neutrinoless muon decays in the presence of nuclei, are
discussed. We focus on the theoretical aspects of $\mu^-(A,Z)\to e^-(A,Z)^*$
(muon-to-electron conversion), one of the most prominent flavour changing
reactions, emphasizing its connection with the physics beyond the standard
model. This process offers the most severe limits of the lepton flavour
violation. By using the nuclear transition matrix elements calculated with
several methods, and the recent experimental data of the branching ratio
$R_{\mu e^-}$, we determine limits for the flavour changing parameters entering
the elementary sector part of $R_{\mu e^-}$. These results are discussed in
view of the ongoing experiment at PSI and the designed at Brookhaven, which are
expected to push down by some orders of magnitude the experimental sensitivity
the next few years with the hope to see ``new physics''.


title: Strange Particles in Dense Matter and Kaon Condensates

abstract:
  We discuss the role of strangeness in dense matter and especially in neutron
stars. The early (in density) introduction of hyperons found in many
calculations is probably delayed by the decrease in vector mean field acting on
the neutron. The decrease results from both conventional many-body rescattering
effects and from the movement towards asymptotic freedom at high densities.
Subthreshold $K^-$-meson production by the KaoS collaboration at GSI shows that
the $K^-$-mass must be substantially lowered, by $\gtrsim$ 200 MeV at $\rho\sim
2\rho_0$. It is shown that explicit chiral symmetry breaking through the kaon
mass may be responsible for $\Sigma^-$-nucleon and $\Xi^-$-nucleon scalar
attraction being weaker than obtained by simple quark scaling. The normal mode
of the strangeness minus, charge $e^-$, excitation is constructed as a linear
combination of $K^-$-meson and $\Sigma^-$, neutron-hole state. Except for zero
momentum, where the terms are unmixed the "kaesobar" is a linear combination of
these two components.


title: Triton photodisintegration with realistic potentials

abstract:
  The photodisintegration of $^{3}$H is treated by means of coupled integral
equations using separable versions of the Paris and the Bonn potentials in
their kernel. The differential cross section for the inverse reaction is
obtained via detailed balance. For the latter process good agreement with the
data is found when including final-state interaction, meson exchange currents,
higher partial waves in the potential, and electric quadrupole contributions in
the electromagnetic interaction.


title: Photodisintegration of three- and four- nucleon systems

abstract:
  Three- and four-nucleon photodisintegration processes are quite efficiently
treated by means of effective two-body integral equations in momentum space. We
recall some aspects of their derivation, present previous and most recent
results obtained within this framework, and discuss general features, trends
and effects observed in these investigations: At low energies final-state
interaction plays an important role. Even more pronounced is the effect of
meson exchange currents. A considerable potential dependence shows up in the
low-energy peak region. The different peak heights are found to be closely
correlated with the corresponding binding energies. Above the peak region only
the difference between potentials with or without p-wave contributions remains
relevant. In the differential cross sections the electric quadrupole
contributions have to be taken into account. The remarkable agreement between
theory and experiment in $p$-$d$ radiative capture is achieved only when
incorporating this contribution, together with most of the above-mentioned
effects. In the final part of this report we briefly review also methods
developed, and results achieved in three- and four- nucleon
electrodisintegration. We, in particular, compare them with a recent access to
this problem, based on the construction of nucleon-nucleus potentials via
Marchenko inversion theory.


title: Triple collisions (e+p+Be7) in solar plasma

abstract:
  Several nuclear reactions involving the Be7 nucleus, not included into the
standard model of the pp-chain, are discussed. A qualitative analysis of their
possible influence on the fate of the Be7 in solar plasma and of their role in
the interpretation of the solar neutrino experiments is given. As an example,
the reaction rate of the nonradiative production of B8 in the triple collision
p + e^- + Be7 ---> B8 + e^- is estimated in the framework of the adiabatic
approximation. For the solar interior conditions the triple collision reaction
rate is approximately 10^{-4} of that for the binary process p + Be7 ---> B8 +
gamma .


title:
Can one learn anything from proton-proton bremsstrahlung? Comment on H.
  W. Fearing preprint nucl-th/9710061

abstract:
  Recently, Fearing (nucl-th/9710061) has argued that, as a matter of
principle, proton-proton bremsstrahlung can yield no more information about the
off-shell properties of the nucleon-nucleon interaction than can already be
deduced from the on-shell properties. In this note we challenge Fearing's
conclusion.


title:
Relativistic three-body bound states and the reduction from four to
  three dimensions

abstract:
  Beginning with an effective field theory based upon meson exchange, the
Bethe-Salpeter equation for the three-particle propagator (six-point function)
is obtained. Using the one-boson-exchange form of the kernel, this equation is
then analyzed using time-ordered perturbation theory, and a three-dimensional
equation for the propagator is developed. The propagator consists of a
pre-factor in which the relative energies are fixed by the initial state of the
particles, an intermediate part in which only global propagation of the
particles occurs, and a post-factor in which relative energies are fixed by the
final state of the particles. The pre- and post-factors are necessary in order
to account for the transition from states where particles are off their mass
shell to states described by the global propagator with all of the particle
energies on shell. The pole structure of the intermediate part of the
propagator is used to determine the equation for the three-body bound state: a
Schr{\"o}dinger-like relativistic equation with a single, global Green's
function. The role of the pre- and post-factors in the relativistic dynamics is
to incorporate the poles of the breakup channels in the initial and final
states. The derivation of this equation by integrating over the relative times
rather than via a constraint on relative momenta allows the inclusion of
retardation and dynamical boost corrections without introducing unphysical
singularities.


title: Photodisintegration of the triton with realistic potentials

abstract:
  The process $\gamma + t \to n + d$ is treated by means of three-body integral
equations employing in their kernel the W-Matrix representation of the
subsystem amplitudes. As compared to the plane wave (Born) approximation the
full solution of the integral equations, which takes into account the final
state interaction, shows at low energies a 24% enhancement. The calculations
are based on the semirealistic Malfliet-Tjon and the realistic Paris and Bonn B
potentials. For comparison with earlier calculations we also present results
for the Yamaguchi potential. In the low-energy region a remarkable potential
dependence is observed, which vanishes at higher energies.


title: Polarization observables in the reaction $NN \to NN \Phi$

abstract:
  We study the reaction $NN \to NN \Phi$ slightly above the threshold within an
extended one-boson exchange model which also accounts for $uud$ knock-out. It
is shown that polarization observables, like the beam-target asymmetry, are
sensible quantities for identifying a $s \bar s$ admixture in the nucleon wave
function on the few per cent level.


title:
Bremsstrahlung in intermediate-energy nucleon reactions within an
  effective one-boson exchange model

abstract:
  Within a covariant effective one-boson exchange model for the $T$ matrix of
$NN$ interactions we present detailed calculations of bremsstrahlung cross
sections for proton - proton and proton - neutron reactions at beam energies in
the 1 GeV region. Besides pure bremsstrahlung processes we consider photons
from $\Delta$ decays and contributions from the $\eta \to \gamma \gamma$
process. At beam energies above 700 MeV the $\Delta$ decay channel dominates
the spectra at large photon energies, where the interference between
non-resonance processes and the $\Delta$ decay channel becomes also important.
Low energy photons stem from pure bremsstrahlung processes. The available
experimental data at 730 MeV beam energy is well described. We extrapolate the
model down to 280 MeV, where more detailed experimental data exist, and find
agreement with angular distributions.


title: Estimates of dilepton spectra from open charm and bottom decays

abstract:
  The spectra of lepton pairs from correlated open charm and bottom decays in
ultrarelativistic heavy-ion collisions are calculated. Our approach includes
energy loss effects of the fast heavy quarks in deconfined matter which are
determined by temperature and density of the expanding parton medium. We find a
noticeable suppression of the initial transverse momentum spectrum of heavy
quarks due to the energy loss within the central rapidity covered by the PHENIX
detector system. As a result the dilepton yields from correlated decays of
heavy quarks are in the same order of magnitude as the Drell-Yan signal.


title: Medium dependence of the bag constant in the quark-meson coupling model

abstract:
  Possible variations of the quark-meson coupling (QMC) model are examined in
which the bag constant decreases in the nuclear medium. The reduction is
supposed to depend on either the mean scalar field or the effective mass of the
nucleon. It is shown that the electric and magnetic radii of the bound nucleon
are almost linearly correlated with the bag constant. Using the fact that the
size of the bound nucleon inside a nucleus is strongly constrained by
$y$-scaling data in quasielastic, electron-nucleus scattering, we set a limit
for the reduction allowed in the bag constant for these two models. The present
study implies that the bag constant can decrease up to 10--17 % at average
nuclear density, depending on the details of the model.


title:
Transitions between complex configurations in the excitation of the
  Double Giant Resonance

abstract:
  The transitions between complex configurations, to which the giant dipole
resonance (GDR) and the double giant dipole resonance (DGDR) doorway states are
coupled, are taken into account in second order perturbation theory for the
reaction amplitude. It is proved that only transitions between GDR and DGDR
doorway states play an essential role in the Coulomb excitation of the DGDR.


title:
Two photons decay of the glueball and scalar isoscalar mesons in a
  scaled NJL model

abstract:
  We use a modified version of the Nambu--Jona-Lasinio model which implements
the QCD trace anomaly to calculate the two photons decay width of the glueball
(f_0(1500)) and of the two scalar mesons (f_0(1370), f_{J=0}(1710)) to which it
is mixed. We investigate the effect of this mixing over the coupling constants
of the f_0 states to the quarks.


title:
Hadronic matter compressibility from event-by-event analysis of
  heavy-ion collisions

abstract:
  We propose a method to measure the hadronic matter compressibility by means
of the event-by-event analysis of heavy-ion collisions at high energies. The
method, which utilizes the thermodynamical relation between the compressibility
and the particle number fluctuations, requires a simultaneous measurement of
the particle source size, temperature and particle multiplicity.


title: $NNK$ and $\Lambda\Lambda K$ Amplitudes in Chiral Perturbation Theory

abstract:
  We explore the S-wave and P-wave amplitudes for $NNK$ and $\Lambda\Lambda K$
interactions using chiral perturbation theory to ${\cal O}(m_s\log m_s)$. In
contrast to the large corrections found in P-wave amplitudes in the nonleptonic
decay of octet baryons, the $NNK$ amplitudes receive only small corrections to
their tree-level values. The uncertainty in the $\Lambda\Lambda K$ amplitudes
is found to be large.


title:
Excitation energy of superdeformed bands in Relativistic Mean Field
  Theory

abstract:
  Constrained Relativistic Mean Field (RMF) calculations have been carried out
to estimate excitation energies relative to the ground state for superdeformed
bands in the mass regions A $\sim$ 190 and A $\sim$ 150. It is shown that RMF
theory is able to successfully reproduce the recently measured superdeformed
minima in Hg and Pb nuclei.


title: Nuclear physics input for solar models

abstract:
  We discuss microscopic cluster model descriptions of two solar nuclear
reactions, Be7(p,gamma)B8 and He3(He3,2p)He4. The low-energy reaction cross
section of Be7(p,gamma)B8, which determines the high-energy solar neutrino
flux, is constrained by Be7 and B8 observables. Our results show that a small
value of the zero-energy cross section is rather unlikely. In He3(He3,2p)He4 we
study the effects of a possible virtual state on the cross section. Although,
we have found no indication for such a state so far, its existence cannot be
ruled out yet. We calculate the He3(He3,2p)He4 and H3(H3,2n)He4 cross sections
in a continuum-discretized coupled channel approximation, and find a good
general agreement with the data.


title:
Relativistic Hartree-Bogoliubov description of ground-state properties
  of Ni and Sn isotopes

abstract:
  The Relativistic Hartree Bogoliubov (RHB) theory is applied in the
description of ground-state properties of Ni and Sn isotopes. The NL3 parameter
set is used for the effective mean-field Lagrangian, and pairing correlations
are described by the pairing part of the finite range Gogny interaction D1S.
Fully self-consistent RHB solutions are calculated for the Ni ($28\leq N\leq
50$) and Sn ($50\leq N\leq 82$) isotopes. Binding energies, neutron separation
energies, and proton and neutron $rms$ radii are compared with experimental
data. The model predicts a reduction of the spin-orbit potential with the
increase of the number of neutrons. The resulting energy splittings between
spin-orbit partners are discussed, as well as pairing properties calculated
with the finite range effective interaction in the $pp$ channel.


title: The ground state of medium-heavy nuclei with non central forces

abstract:
  We study microscopically the ground state properties of 16O and 40Ca nuclei
within correlated basis function theory. A truncated version of the realistic
Urbana v14 (U14) potential, without momentum dependent terms, is adopted with
state dependent correlations having spin, isospin and tensor components. Fermi
hypernetted chain integral equations and single operator chain approximation
are used to evaluate one- and two-body densities and ground state energy. The
results are in good agreement with the available variational MonteCarlo data,
providing a first substantial check for the accuracy of the cluster expansion
method with state dependent correlations. The finite nuclei treatment of non
central interactions and correlations has, at least, the same level of accuracy
as in infinite nuclear matter. The binding energy for the full U14+TNI
interaction is computed, addressing its small momentum dependent contributions
in local density approximation. The nuclei are underbound by about 1 MeV per
nucleon. Further energy lowering might be achieved by a more accurate
variational minimization.


title: $Q^2$--Dependence of the Gerasimov-Drell-Hearn Sum Rule

abstract:
  We test the Gerasimov-Drell-Hearn (GDH) sum rule numerically by calculating
the total photon absorption cross sections $\sigma_{1/2}$ and $\sigma_{3/2}$ on
the nucleon via photon excitation of baryon resonances in the constituent quark
model. A total of seventeen, low-lying, non-strange baryon resonances are
included in this calculation. The transverse and longitudinal interference
cross section, $\sigma_{1/2}^{TL}$, is found to play an important role in the
study of the $Q^2$ variation of the sum rule. The results show that the GDH sum
rule is saturated by these resonances at a confidence level of 94%. In
particular, the $P_{33}(1232)$ excitation largely saturates the sum rule at
$Q^2 = 0$, and dominates at small $Q^2$. The GDH integral has a strong
$Q^2$-dependence below $Q^2= 1.0 {GeV}^2$ and changes its sign around $Q^2= 0.3
{GeV}^2$. It becomes weakly $Q^2$-dependent for $Q^2 > 1.0 {GeV}^2$ because of
the quick decline of the resonance contributions. We point out that the $Q^2$
variation of the GDH sum rule is very important for understanding the nucleon
spin structure in the non-perturbative QCD region.


title: Off-shell effects in the electromagnetic production of strangeness

abstract:
  Previous approaches to the photo- and electro-production of strangeness off
the proton, based upon effective hadronic Lagrangians, are extended here to
incorporate the so called off-shell effects inherent to the fermions with spin
>= 3/2. A formalism for intermediate-state, spin 3/2, nucleonic and hyperonic
resonances is presented and applied to the processes $\gamma + p ---> K^{+} +
\Lambda$, for $E_{\gamma}^{lab}$ <= 2.5 GeV, $e + p ---> e' + K^+ + \Lambda$,
as well as the branching ratio for the crossed channel reaction $K^- + p --->
\gamma + \Lambda$, with stopped kaons. The sensitivity, from moderate to
significant, of various observables to such effects are discussed.


title: Translationally-invariant coupled-cluster method for finite systems

abstract:
  The translational invariant formulation of the coupled-cluster method is
presented here at the complete SUB(2) level for a system of nucleons treated as
bosons. The correlation amplitudes are solution of a non-linear coupled system
of equations. These equations have been solved for light and medium systems,
considering the central but still semi-realistic nucleon-nucleon S3
interaction.


title:
On the binding energy of double \Lambda hypernuclei in the relativistic
  mean field theory

abstract:
  We calculate the binding energy of two $\Lambda$ hyperons bound to a nuclear
core within the relativistic mean field theory. The starting point is a
two-body relativistic equation of the Breit type suggested by the RMFT, and
corrected for the two-particle interaction. We evaluate the 2 $\Lambda$
correlation energy and estimate the contribution of the $\sigma^*$ and $\Phi$
mesons, acting solely between hyperons, to the bond energy
  $\Delta{B_{\Lambda\Lambda}}$ of $^6_{\Lambda\Lambda}He$,
  $^{10}_{\Lambda\Lambda}Be$ and $^{13}_{\Lambda\Lambda}B$. Predictions of the
$\Delta{B_{\Lambda\Lambda}}$ A dependence are made for heavier
$\Lambda$-hypernuclei.


title:
Nuclear transparency in quasielastic A(e,e'p): intranuclear cascade
  versus eikonal approximation

abstract:
  The problem of nuclear propagation through the nuclear medium in quasielastic
A(e,e'p) reactions is discussed in the kinematic range 1<Q^2<7 (GeV/c)^2. The
coefficient of nuclear transparency is calculated for each Q^2 in the framework
of the intranuclear cascade model (INC) and of the eikonal approximation (EA).
The predictions of both models are in good agreement with each other and with
experimental data recently obtained at SLAC, BATES and TJNAF. The EA gives an
explanation of the Q^2 behaviour of the transparency coefficient as a kinematic
effect related to the superposition of contributions from each target shell.


title: Double giant resonances in deformed nuclei

abstract:
  We report on the first microscopic study of the properties of two-phonon
giant resonances in deformed nuclei. The cross sections of the excitation of
the giant dipole and the double giant dipole resonances in relativistic heavy
ion collisions are calculated. We predict that the double giant dipole
resonance has a one-bump structure with a centroid 0.8 MeV higher than twice
energy for the single giant dipole resonance in the reaction under
consideration. The width of the double resonance equals to 1.33 of that for the
single resonance.


title: Nucleon resonances in the constituent quark model with chiral symmetry

abstract:
  The mass spectra of nucleon resonances with spin 1/2, 3/2, and 5/2 are
systematically studied in the constituent quark model with meson-quark
coupling, which is inspired by the spontaneous breaking of chiral symmetry of
QCD.
  The meson-quark coupling gives rise not only to the one-meson-exchange
potential between quarks but also to the self-energy of baryon resonances due
to the existence of meson-baryon decay channels.
  The two contributions are consistently taken into account in the calculation.
  The gross properties of the nucleon resonance spectra are reproduced fairly
well although the predicted mass of N(1440) is too high.


title:
N-Nucleon Effective Generators of the Poincare Group Derived from a
  Field Theory

abstract:
  It is shown that the ten generators of the Poincare group acting in the Fock
space of nucleons and mesons and based on standard Lagrangians can be
blockdiagonalized by one and the same unitary transformation such that the
space of a fixed number of nucleons is separated from the rest of the Fock
space. The existence proof is carried through in a formal power series
expansion in the coupling constant to all orders. In this manner one arrives at
effective generators of the Poincare group which act in the two subspaces
separately.


title: In-medium kaon and antikaon properties in the quark-meson coupling model

abstract:
  The properties of the kaon, $K$, and antikaon, $\kbar$, in nuclear medium are
studied in the quark-meson coupling (QMC) model. Employing a constituent
quark-antiquark (MIT bag model) picture, their excitation energies in a nuclear
medium at zero momentum are calculated within mean field approximation. The
scalar, and the vector mesons are assumed to couple directly to the nonstrange
quarks and antiquarks in the $K$ and $\kbar$ mesons. It is demonstrated that
the $\rho$ meson induces different mean field potentials for each member of the
isodoublets, $K$ and $\kbar$, when they are embedded in asymmetric nuclear
matter. Furthermore, it is also shown that this $\rho$ meson potential is
repulsive for the $K^-$ meson in matter with a neutron excess, and renders
$K^-$ condensation less likely to occur.


title:
Violation of the $\Delta$I=1/2 rule in the nonmesonic weak decay of
  $\Lambda$ hypernuclei

abstract:
  Violations of the $\Delta$I=1/2 rule are investigated in the nonmesonic weak
hypernuclear decay using a weak $\Lambda$N$\to$NN transition potential based on
meson exchange. While the weak $\Delta$I=3/2 matrix elements of baryons with
pseudoscalar mesons are known to be very small, the same matrix elements of
baryons with vector mesons, evaluated in the factorization approximation, are
found to be significant. Within the uncertainties of the factorization
approximation we find that the total rate increases by at most 6% lying within
the error bars of the more recent experimental result. The neutron- to
proton-induced rate, on the other hand, can change by up to a factor of two,
while the asymmetry parameter is strongly affected as well.


title: Meson $m_T$-scaling in heavy-ion collisions at SIS energies

abstract:
  We perform systematical studies on transverse-mass spectra of $\pi^0$,
$\eta$, $\omega$, $\phi$, $K^+$ and $K^-$ mesons for C + C, Ni + Ni, Au + Au
collisions at SIS energies within the HSD transport approach. We find that the
$m_T$-spectra sensitively reflect the in-medium properties of the mesons. The
'bare mass' scenario leads to a general scaling behaviour for the meson
$m_T$-spectra when including a mass shift due to the associate strangeness
production threshold for kaons and antikaons whereas a 'dropping' mass scheme
violates this $m_T$-scaling. The relative slope parameters, however, provide
valuable information about the average meson potentials in the nuclear medium.


title:
Chiral nonperturvative approach to the isoscalar s-wave pion-pion
  interaction in a nuclear medium

abstract:
  The s-wave isoscalar amplitude for pion-pion scattering in a nuclear medium
is evaluated using a nonperturbative unitary coupled channels method and the
standard chiral Lagrangians. The method has proved successful to describe the
pion-pion properties in the scalar isoscalar channel up to 1.2 GeV giving rise
to poles in the t matrix for the f0(980) and the sigma. The extension of the
method to the nuclear medium implies not only the renormalization of the pions
in the medium, but also the introduction of interaction terms related to
contact terms in the pion-nucleon to pion-pion-nucleon interaction. Off shell
effects are also shown to be important leading to cancellations which reduce
the coupled channel integral equations to a set of algebraic equations. As the
density increases we find a reduction of strength below the $\sigma$ region and
a certain accumulation of strength at energies around pion threshold. Our
results, based on chiral Lagrangians, provide similar results to those obtained
with phenomenological models which impose minimal chiral constraints.


title:
Electromagnetic Probes of Dense Matter in Relativistic Heavy-Ion
  Collisions

abstract:
  Dilepton and photon production in heavy-ion collisions at SPS energies is
studied in the relativistic transport model that incorporates self-consistently
the change of hadron masses in dense matter. It is found that the dilepton
spectra in proton-nucleus reactions can be well described by the conventional
mechanisms of Dalitz decay, primary vector meson decay, decay of charmed
mesons, and the initial Drell-Yan processes. However, to provide a quantitative
explanation of the observed dilepton spectra in central heavy-ion collisions
requires contributions other than these direct decays and also various medium
effects. Introducing a decrease of vector meson masses in hot dense medium, we
find that the low-mass dilepton enhancement can be satisfactorily explained.
Furthermore, to explain the intermediate-mass dilepton enhancement in heavy-ion
collisions, secondary processes such as $\pi a_1\to l{\bar l}$ are found to be
very important. Finally, the single photon spectra in our calculations with
either free or in-medium meson masses do not exceed the upper limit measured by
the WA80 Collaboration.


title: Solar and Supernova Constraints on Cosmologically Interesting Neutrinos

abstract:
  The sun and core-collapse supernovae produce neutrino spectra that are
sensitive to the effects of masses and mixing. Current results from solar
neutrino experiments provide perhaps our best evidence for such new neutrino
physics, beyond the standard electroweak model. I discuss this evidence as well
as the limited possibilities for more conventional explanations. If the
resolution of the solar neutrino problem is $\nu_e \to \nu_\mu$ oscillations,
standard seesaw estimates of $m_{\nu_\tau}$ suggest a cosmologically
interesting third-generation neutrino. I discuss recent nucleosynthesis
arguments that lead to an important constraint on this possibility.


title: A Method to Study `Chemical' Fluctuations in Nucleus--Nucleus Collisions

abstract:
  A method to study event--by--event fluctuations of the `chemical' (particle
type) composition of the final state of high energy collisions is proposed.}


title: $\pi\pi$ scattering in the $\rho$-meson channel at finite temperature

abstract:
  We study $\pi\pi$ scattering in the I=1, $J^P=1^-$ channel at finite
temperature in the framework of the extended Nambu-Jona-Lasinio model that
explicitly includes vector and axial-vector degrees of freedom in addition to
the usual scalar and pseudoscalar sector. The S-matrix in the coupled channels
$q\bar q$ and $\pi \pi$ is constructed via $\rho$-exchange in the $s$-channel.
The self-energy of the $\rho$-meson contains both quark and pion loop
contributions. The analytic structure of the S-matrix for $T\geq 0$ is
investigated and the motion of the $\rho$-pole as a function of coupling
constant and temperature is followed in the complex $\sqrt{s}$-plane. For
numerical calculations, parameters are chosen in order that $m_\pi$, $f_\pi$
and the experimental $\pi\pi$ phase shifts $\delta_1^1$ at zero temperature are
reproduced, and then the behavior of the $\rho$-pole as well as the $\pi\pi$
cross section is investigated as a function of the temperature. We find that
the position of the $\rho$ mass stays practically constant for $0\leq T\leq
130$ MeV, and then moves down in energy by about 200 MeV for 130 MeV$\leq T\leq
230$ MeV.


title: Confronting particle emission scenarios with strangeness data

abstract:
  We show that a hadron gas model with continuous particle emission instead of
freeze out may solve some of the problems (high values of the freeze out
density and specific net charge) that one encounters in the latter case when
studying strange particle ratios such as those by WA85. This underlines the
necessity to understand better particle emission in hydrodynamics to be able to
analyze data. It also re-opens the possibility of a quark-hadron transition
occuring with phase equilibrium instead of explosively.


title: Can we see the hadron-quark transition happening in neutron stars?

abstract:
  In order to actually see the hadron-quark transition happening in a neutron
star, we point out and study two static conditions (the transition hadronic
density must be lower than the neutron star maximum hadronic density; the
neutron star mass at the transition hadronic density must be in the observed
range, of order 1.4 solar mass) and one dynamical condition (nucleation must
occur during the star lifetime). We find that the mini-colapse acompanying the
transition from metastable hadronic matter to quark matter may be relevant to
explain macro-glitches and gamma ray bursts, but that the mecanism increasing
the star density must be relatively fast, e.g. accretion but not slowing down.
This rules out a scenario for gamma ray bursts proposed recently.


title:
$\Xi^{-} d\to n\Lambda\Lambda$ and the $\Lambda\Lambda$ final state
  interaction

abstract:
  The reaction $\Xi^-d\to n\Lambda\Lambda$ is studied within the framework of
the Faddeev equations as a possible tool to gain insight into the final state
$\Lambda$--$\Lambda$ interaction. The neutron differential energy spectrum
gives a final state interaction that is sensitive to both the
$\Lambda$--$\Lambda$ amplitude at threshold, and the coupling between the
$\Lambda$--$\Lambda$ and $\Xi$--$N$ channels. The latter is a result of
interference between two mechanisms for the production of the final state,
which suggests that this reaction could give a measure of flavor SU(3)
violation in the two-baryon system.


title: Phaseshift equivalent NN potentials and the deuteron

abstract:
  Different modern phase shift equivalent NN potentials are tested by
evaluating the partial wave decomposition of the kinetic and potential energy
of the deuteron. Significant differences are found, which are traced back to
the matrix elements of the potentials at medium and large momenta. The
influence of the localisation of the one-pion-exchange contribution to these
potentials is analyzed in detail.


title:
Isospin Dependence of Proton and Neutron Radii within Relativistic Mean
  Field Theory

abstract:
  The binding energies, shapes and sizes of even-even beta-stable nuclei with A
>= 40 and a few chains of isotopes with Z=50, 56, 82, 94 protons and isotones
with N=50, 82, 126 neutrons are analyzed. The average isospin dependence of the
radii of protons and neutrons evaluated within the relativistic mean field
theory is studied. A simple, phenomenological formula for neutron radii is
proposed.


title:
Proton Polarization in the $p(\vec e,e'\vec p)\pi^0$ Reaction and the
  Measurement of Quadrupole Components in the N to $\Delta$ Transition

abstract:
  The recoil proton polarization in the $\pi^0$ production off the proton with
longitudinally polarized electron beam has been studied as a means to measure
quadrupole components in the N to $\Delta$ transition. On top of the $\Delta$
resonance a high sensitivity to a possible Coulomb quadrupole excitation is
found in parallel kinematics. The ratio of $S_{1+}/M_{1+}$ multipole amplitudes
can be determined from the ratio of the two in-scattering-plane recoil proton
polarization components. Avoiding the absolute measurement of the
polarizations, such a ratio allows small experimental uncertainties.
Furthermore, the electron helicity independent proton polarization component
enables the characterization of resonant and non-resonant pieces.


title: Charged current weak electroproduction of Delta resonance

abstract:
  We study the weak production of $\Delta$ (i.e. $e^{-} + p \to \Delta^{0}+
\nu_{e}$ and $e^{+} + p \to \Delta^{++} + \bar{\nu}_{e}$) in the intermediate
energy range corresponding to the Mainz and TJNAF electron accelerators. The
differential cross sections $\sigma(\theta)$ are found to be of the order of $
10^{-39}$ cm$^2$/sr, over a range of angles which increases with energy. The
possibility of observing these reactions with the high luminosities available
at these accelerators, and studying the weak N-$\Delta$ transition form factors
through these reactions is discussed. The production cross section of
N$^*(1440)$ in the kinematic region of $\Delta$ production is also estimated
and found to be small.


title: Testing the Core-Halo Model on Bose-Einstein Correlation Functions

abstract:
  Having first performed a Monte Carlo simulation to justify the analysis
technique to be used, we then analyze the Bose-Einstein correlation functions
from CERN experiment NA44 in the context of the core-halo model. Although
experimental resolution and error bar distribution prevents a direct
observation of the halo structure, the values for the core radius and the core
fraction of pions can be obtained in a straight-forward manner. These are found
to be independent of the structure of the correlation function at small
relative momenta of Q < 50 MeV. Hence, the omega meson decay products do not
distort the Gaussian shape of the Bose-Einstein correlation function in S + Pb
-> pi + pi + X reaction at CERN SPS. As we find that the "model-independent"
HBT radii yield results that are quantitatively as well as qualitatively
unreliable for systems with long-lived resonances, we present their corrected
form that applies for correlation functions with lambda(K) < 1.


title:
Relativistic Study of Medium Polarization Effects on Superfluidity in
  Nuclear Matter

abstract:
  Effects of the Fermi-sea polarization on the superfluidity in nuclear matter
are studied in a framework of quantum hadrodynamics. The particle-hole
polarization due to $\sigma$ and $\omega$ mesons enhances the peak value of the
pairing gap contrary to the previous non-relativistic studies.


title: Dilepton from Disoriented Chiral Condensates

abstract:
  Disoriented chiral condensates are manifested as long wavelength pionic
oscillations and their interaction with the thermal environment can be a
significant source of dileptons. We calculate the yield of such dilepton
production within the linear sigma model and illustrate the basic features of
the dilepton spectrum in a schematic model. We find that the dilepton yield
with invariant mass near and below $2m_{\pi}$ due to the soft pion modes can be
up to two orders of magnitude larger than the corresponding equilibrium yield.
We conclude with a discussion on how this enhancement can be detected by
present dilepton experiments.


title: Analysis of the superdefomed rotational bands

abstract:
  All available experimental data for the $\Delta I=2$ transition energies in
superdeformed bands are analyzed by using a new one-point formula. The
existence of deviations from the smooth behavior is confirmed in many bands.
However, we stress that one cannot necessarily speak about staggering patterns
as they are mostly irregular. Simulations of the experimental data suggest that
the irregularities may stem from the presence of irregular kinks in the
rotational spectra. This could be a clue but, at the moment, where such kinks
come from is an open question.


title:
Relativistic Mean Field Description of Nuclear Collective Rotation -The
  Superdeformed Rotational Bands in the A$\sim$60 Mass Region-

abstract:
  Relativistic Mean Field Theory is applied to the description of rotating
nuclei. Since the previous formulation of Munich group was based on a special
relativistic transformation property of the spinor fields, we reformulate in a
fully covariant manner using tetrad formalism. The numerical calculations are
performed for 3 zinc isotopes, including the newly discovered superdeformed
band in $^{62}$Zn which is the first experimental observation in this mass
region.


title:
Radiative processes of nucleon interactions and possible existence of
  exotic dibaryons

abstract:
  The cross section of the reaction $pp \to pp \gamma \gamma$ is estimated and
the exploration possibilities of this reaction to probe for a possible
excitation of subnuclear degrees of freedom in two-nucleon systems, in
particular, the production and decay of the NN-decoupled dibaryon resonances,
are briefly discussed.Some arguments for and implications of the intermediate
dibaryon resonance excitation are inferred from preliminary data on the
two-photon yield and energy distribution observed by the DIBAR2$\gamma$ -
Collaboration at the kinetic energy of the initial proton $T_{lab} \simeq 200
MeV$.