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The dependence of the transmission coefficient on the deformation, the collective rotation and excitation energy of the compound nucleus emitting light particles is introduced in the framework of Wei{\ss}kopf's evaporation theory. The competition between fission and particle evaporation is treated by a~Langevin equation for the fission variable coupled to the emission process. Detailed calculations are presented on the decay of different Gd and Yb isotopes at an excitation energy of about 250~MeV. These calculations demonstrate the importance of the effects of nuclear deformation and of the initial spin distribution on the evaporation.
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arxiv:nucl-th/9602040
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We study the strong couplings of the nucleon and delta resonances in a collective model. In the ensuing algebraic treatment we derive closed expressions for decay widths which are used to analyze the experimental data for strong decays into the pion and eta channels.
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arxiv:nucl-th/9603015
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The generating functional of heavy baryon chiral perturbation theory at order O(Q^2) in the mean field approximation (with a pseudoscalar source coupling which is consistent with the PCAC-Ward identities on the current quark level) has been exploited to derive Migdal's in--medium pion propagator. It is shown that the prediction for the density dependence of the quark condensate obtained on the composite hadron level by embedding PCAC within the framework of Migdal's approach to finite Fermi systems is identical to that resulting from QCD.
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arxiv:nucl-th/9603017
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We revisit sidewise dispersion relations as a method to relate the nucleon off-shell form factor to observable quantities, namely the meson-nucleon scattering phase shifts. It is shown how for meson-nucleon scattering a redefinition of the intermediate fields leaves the scattering amplitude invariant, but changes the behavior of the off-shell form factor as expressed through dispersion relations, thus showing representation dependence. We also employ a coupled-channel unitary model to test the validity of approximations concerning the influence of inelastic channels in the sidewise dispersion relation method.
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arxiv:nucl-th/9603031
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Starting from full quantum field theory, various mean field approaches are derived systematically. With a full consideration of external source dependence, the stationary phase approximation of an action gives a nuclear mean field theory which includes quantum correlation effects (such as particle-hole or ladder diagram) in a simpler way than the Brueckner-Hartree-Fock approach. Implementing further approximation, the result can be reduced to Hartree-Fock or Hartree approximation. The role of the source dependence in a mean field theory is examined.
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arxiv:nucl-th/9604007
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Within the framework of Classical Molecular Dynamics, we study the collision Au + Au at an incident energy of 35 MeV/nucleon. It is found that the system shows a critical behaviour at peripheral impact parameters, revealed through the analysis of conditional moments of charge distributions, Campi Scatter Plot, and the occurrence of large fluctuations in the region of the Campi plot where this critical behaviour is expected. When applying the experimental filters of the MULTICS-MINIBALL apparatus, it is found that criticality signals can be hidden due to the inefficiency of the experimental apparatus. The signals are then recovered by identifying semi-peripheral and peripheral collisions looking to the velocity distribution of the largest fragment, then by selecting the most complete events.
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arxiv:nucl-th/9604029
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We re-examine the matter radii of diffuse halo nuclei, as deduced from reaction cross section measurements at high energy. Careful consideration is given to the intrinsic few-body structure of these projectiles and the adiabatic nature of the projectile-target interaction. Using $^{11}$Li, $^{11}$Be and $^{8}$B as examples we show that data require significantly larger matter radii than previously reported. The revised value for $^{11}$Li of 3.55 fm is consistent with three-body models with significant $1s$-intruder state components, which reproduce experimental $^{9}$Li momentum distributions following $^{11}$Li breakup, but were hitherto thought to be at variance with cross section data.
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arxiv:nucl-th/9604033
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The dynamics of a hadronizing quark matter drop is investigated with a hybrid-like model, which takes into account equilibrium as well as non-equilibrium features of the process. We study the the particle rates from the hadronizing plasma, which have to be put in relation to the whole time evolution of the system. The impact of finite-size effects on the distillation process is considered. $H^0$-Dibaryon yields are estimated. Microscopic calculations of hypercluster formation at AGS and SPS are presented.
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arxiv:nucl-th/9606027
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We discuss the elementary physics of the final state Coulomb interactions in Hanbury-Brown Twiss interferometry, showing -- with explicit comparison to E877 data for $\pi^+\pi^-$ and $\pi^\pm p$ -- that the Coulomb corrections in the pair correlation function can be well understood in terms of simple classical physics. We connect the classical picture with descriptions in terms of Coulomb wave functions, and investigate the influence of the ``central'' Coulomb potential on the pair correlation function.
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arxiv:nucl-th/9606055
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We study the reconstruction of the source function in space-time directly from the measured HBT correlation function using the Maximum Entropy Principle. We find that the problem is ill-defined without at least one additional theoretical constraint as input. Using the requirement of a finite source lifetime for the latter we find a new Gaussian parametrization of the source function directly in terms of the measured HBT radius parameters and its lifetime, where the latter is a free parameter which is not directly measurable by HBT. We discuss the implications of our results for the remaining freedom in building source models consistent with a given set of measured HBT radius parameters.
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arxiv:nucl-th/9607037
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We study the production of $K^+, \rho, \omega$ and $\phi$ mesons in $p + ^{12}C$ reactions on the basis of empirical spectral functions. The high momentum, high removal energy part of the spectral function is found to be negligible in all cases close to the absolute threshold. Furthermore, the two-step process ($pN \rightarrow \pi N N; \pi N \rightarrow N + K^+, \rho, \omega, \phi$) dominates the cross section at threshold energies in line with earlier calculations based on the folding model.
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arxiv:nucl-th/9607047
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We review briefly the fundamental equations of a semi-microscopic core-particle coupling method that makes no reference to an intrinsic system of coordinates. We then demonstrate how an intrinsic system can be introduced in the strong coupling limit so as to yield a completely equivalent formulation. It is emphasized that the conventional core-particle coupling calculation introduces a further approximation that avoids what has hitherto been the most time-consuming feature of the full theory, and that this approximation can be introduced either in the intrinsic system, the usual case, or in the laboratory system, our preference. A new algorithm is described for the full theory that largely removes the difference in complexity between the two types of calculation. Comparison of the full and approximate theories for some representative cases provides a basis for the assessment of the accuracy of the traditional approach. We find that for well-deformed nuclei, e.g. 157Gd and 157Tb, the core-coupling method and the full theory give similar results.
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arxiv:nucl-th/9608011
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Momentum distributions of particles from fast three-body halo fragmentation reactions with polarized beams and outgoing fragments are analyzed by use of the sudden approximation. The final state interaction between the two non-disturbed particles is considered. We first give a general and detailed description of the method. We introduce observable quantities that emphasize the two-body correlations in the initial three-body structure as well as in the final two-body system. Using neutron removal from 11Li as an example we investigate the dependence of the polarization observables on the properties of the low-lying resonances and virtual states of the 10Li subsystem. These observables are very sensitive to the l > 0-waves in the wave functions, and they provide detailed information on the resonance structure of the neutron-core subsystem.
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arxiv:nucl-th/9608030
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We summarize the current theoretical and experimental status of the spectral changes of vector mesons ($\rho$, $\omega$, $\phi$) at finite baryon density. Various approaches including QCD sum rules, effective theory of hadrons and bag models show decreasing of the vector meson masses in nuclear matter. Possibility to detect the mass shift through lepton pairs in $\gamma-A$, $p-A$ and $A-A$ reactions are also discussed.
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arxiv:nucl-th/9608037
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Using a self-consistent, Hartree description for both infinite nuclear matter and finite nuclei based on a relativistic quark model (the quark-meson coupling model), we investigate the variation of the masses of the non-strange vector mesons, the hyperons and the nucleon in infinite nuclear matter and in finite nuclei.
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arxiv:nucl-th/9608060
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Within the framework of a relativistic transport model (ART) for heavy-ion collisions at AGS energies, we examine the effects of kaon dispersion relation on the transverse flow of kaons and their transverse momentum and azimuthal angle distributions. We find that the transverse flow is the most sensitive observable for studying the kaon dispersion relation in dense medium.
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arxiv:nucl-th/9609019
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I discuss two-particle intensity interferometry as a method to extract from measured 1- and 2-particle momentum spectra information on the space-time geometry and dynamics of the particle emitting source. Particular attention is given to the rapid expansion and short lifetime of the sources created in relativistic heavy-ion collisions. Model-independent expressions for the HBT size parameters in terms of the space-time variances of the source are derived, and a new parametrization of the correlation function is suggested which allows to separate the transverse, longitudinal and temporal extension of the source and to measure its transverse and longitudinal expansion velocity. The effects of resonance decays are also discussed.
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arxiv:nucl-th/9609029
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We investigate the influence of medium corrections to the pion dispersion relation on the pion dynamics in intermediate energy heavy ion collisions. To do so a pion potential is extracted from the in-medium dispersion relation and used in QMD calculations and thus we take care of both, real and imaginary part of the pion optical potential. The potentials are determined from different sources, i.e. from the $\Delta$--hole model and from phenomenological approaches. Depending on the strength of the potential a reduction of the anti-correlation of pion and nucleon flow in non-central collisions is observed as well as an enhancement of the high energetic yield in transverse pion spectra. A comparison to experiments, in particular to $p_t$-spectra for the reaction Ca+Ca at 1 GeV/nucleon and the pion in-plane flow in Ne+Pb collisions at 800 MeV/nucleon, generally favours a weak potential.
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arxiv:nucl-th/9610027
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Dilepton production in proton- and nucleus-induced reactions is studied in relativistic transport model using initial conditions determined by the string dynamics from RQMD. It is found that both the CERES and HELIOS-3 data for dilepton spectra in proton-nucleus reactions can be well described by the `conventional' mechanism of Dalitz decay and direct vector meson decay. However, to provide a quantitative explanation of the observed dilepton spectra in central S+Au and S+W collisions requires contributions other than these direct decays. Introducing a decrease of vector meson masses in hot and dense medium, we find that these heavy-ion data can also be satisfactorily explained. This agrees with our earlier conclusions based on a fire cylinder model. We also give predictions for Pb+Au collisions at 160 GeV/nucleon using current CERES mass resolution and acceptance.
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arxiv:nucl-th/9611037
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We investigate the chemical equilibration of the parton distributions in collisions of two heavy nuclei. We use initial conditions obtained from a self-screened parton cascade calculation and, for comparison, from the HIJING model. We consider a one-dimensional, as well as a three-dimensional expansion of the parton plasma and find that the onset of the transverse expansion impedes the chemical equilibration. At energies of 100 GeV/nucleon, the results for one-dimensional and three-dimensional expansion are quite similar except at large values of the transverse radius. At energies of several TeV/nucleon, the plasma initially approaches chemical equilibrium, but then is driven away from it, when the transverse velocity gradients develop. We find that the total parton multiplicity density remains essentially unaffected by the flow, but the individual concentrations of quarks, antiquarks, and gluons are sensitive to the transverse flow. The consequences of the flow are also discernible in the transverse momenta of the partons and in the lepton pair spectra, where the flow causes a violation of the so-called $M_T$ scaling.
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arxiv:nucl-th/9611041
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We propose a simple and systematic method to quantize the cranking model and to calculate the matrix elements of intrinsic operators entering the generalized intensity relations. An example of the application is given to show the Coriolis coupling effects for B(E3) values of the 3- octupole states in Gd isotopes.
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arxiv:nucl-th/9612003
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Self consistency in the analysis of transmission measurements for K^+ on several nuclei in the momentum range of 500-700 MeV/c is achieved with a "t_{eff}(rho)rho" potential and new results are derived for total cross sections. The imaginary part of the t_{eff} amplitude is found to increase linearly with the average nuclear density in excess of a threshold value. This phenomenological density dependence of the K^+ nucleus optical potential also gives rise to good agreement with recent measurements of differential cross sections for elastic scattering of 715 MeV/c K^+ by Li^6 and C.
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arxiv:nucl-th/9612008
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We propose a three-potential formalism for the three-body Coulomb scattering problem. The corresponding integral equations are mathematically well-behaved and can succesfully be solved by the Coulomb-Sturmian separable expansion method. The results show perfect agreements with existing low-energy $n-d$ and $p-d$ scattering calculations.
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arxiv:nucl-th/9701027
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Nonperturbative polaron variational methods are applied, within the so-called particle or worldline representation of relativistic field theory, to study scattering in the context of the scalar Wick - Cutkosky model. Important features of the variational calculation are that it is a controlled approximation scheme valid for arbitrary coupling strengths, the Green functions have all the cuts and poles expected for the exact result at any order in perturbation theory and that the variational parameters are simultaneously sensitive to the infrared as well as the ultraviolet behaviour of the theory. We generalize the previously used quadratic trial action by allowing more freedom for off-shell propagation without a change in the on-shell variational equations and evaluate the scattering amplitude at first order in the variational scheme. Particular attention is paid to the $s$-channel scattering near threshold because here non-perturbative effects can be large. We check the unitarity of a our numerical calculation and find it greatly improved compared to perturbation theory and to the zeroth order variational results.
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arxiv:nucl-th/9701036
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At zero-density, meson-nucleon vertex corrections to vacuum polarization are studied in the $\sigma-\omega$ model with the cutoff. It is shown that the properties of the vertex corrections to vacuum polarization are somewhat different from those described by the ordinary renormalization procedures when the cutoff is small (< 5 GeV). The low-energy effective Lagrangian is constructed in the framework of the renormalization group method. The weak tensor and derivative couplings of meson-nucleon interactions may be needed in the low-energy effective theory of mesons and nucleons.
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arxiv:nucl-th/9702001
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A wavepacket model for a system of free pions, which takes into account the full permutation symmetry of the wavefunction and which is suitable for any phase space parametrization is developed. The properties of the resulting mixed ensembles and the two-particle correlation function are discussed. A physical interpretation of the chaoticity lambda as localizat of the pions in the source is presented. Two techniques to generate test-particles, which satisfy the probability densities of the wavepacket state, are studied: 1. A Monte Carlo procedure in momentum space based on the standard Metropolis technique. 2. A molecular dynamic procedure using Bohm's quantum theory of motion. In order to reduce the numerical complexity, the separation of the wavefunction into momentum space clusters is discussed. In this context th influence of an unauthorized factorization of the state, i. e. the omissio of interference terms, is investigated. It is shown that the correlation radius remains almost uneffected, but the chaoticity parameter decreases substantially. A similar effect is observed in systems with high multiplic where the omission of higher order corrections in the analysis of two-part correlations causes a reduction of the chaoticity and the radius. The approximative treatment of the Coulomb interaction between pions and source is investigated. The results suggest that Coulomb effects on the co radii are not symmetric for pion pairs of different charges. For negative the radius, integrated over the whole momentum spectrum, increases substan while for positive pions the radius remains almost unchanged.
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arxiv:nucl-th/9702005
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For a $Q \cdot Q$ interaction the energy weighted sum rule for isovector orbital magnetic dipole transitions is proportional to the difference $\sum B(E2, isoscalar) - \sum B(E2, isovector)$, not just to $\sum B(E2, physical)$. This fact is important in ensuring that one gets the correct limit as one goes to nuclei, some of which are far from stability, for which one shell (neutron or proton) is closed. In $0p$ shell calculations for the even-even Be isotopes it is shown that the Fermion SU(3) model and Boson SU(3) model give different results for the energy weighted scissors mode strengths.
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arxiv:nucl-th/9702017
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The contribution of the $\Delta$(1232) isobar to the electromagnetic current of the two-nucleon system and its role in ($\gamma$,NN) processes is investigated. The difference between the genuine $\Delta$-excitation current and that part of the current connected to the deexcitation of a preformed $\Delta$ in the target nucleus is stressed. The latter cannot lead to a resonant behaviour of matrix elements for energies in the $\Delta$ region. The reaction $^{16}O(\gamma,pp)^{14}C$, where the $\Delta$ contribution is dominant at intermediate energies, is considered. The large variations found in the cross sections for different treatments stress the need for a proper treatment of the $\Delta$ current for a clear understanding of the reaction mechanism of two-nucleon emission processes.
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arxiv:nucl-th/9702031
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Asymmetric nuclear matter is treated in the formalism of Dirac-Brueckner approach with Bonn one-boson-exchange nucleon-nucleon interaction. We extract the symmetry energy coefficient at the saturation to be about 31 MeV, which is in good agreement with empirical value of $30\pm 4$ MeV. The symmetry energy is found to increase almost linearly with the density, which differs considerably from the results of non-relativistic approaches. This finding also supports the linear parameterization of Prakash, Ainsworth and Lattimer. We find, furthermore, that the higher-order dependence of the nuclear equation of state on the asymmetry parameter is unimportant up to densities relevant for neutron stars. The resulting equation of state of neutron-rich matter is used to calculate the maximum mass of neutron star, and we find it to be about 2.1$M_\odot$. Possible mechanisms for the softening of the equation of state are also discussed.
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arxiv:nucl-th/9703034
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We address the dynamics of damped collective modes in terms of first and second moments. The modes are introduced in a self-consistent fashion with the help of a suitable application of linear response theory. Quantum effects in the fluctuations are governed by diffusion coefficients D_{\mu\nu}. The latter are obtained through a fluctuation dissipation theorem generalized to allow for a treatment of unstable modes. Numerical evaluations of the D_{\mu\nu} are presented. We discuss briefly how this picture may be used to describe global motion within a locally harmonic approximation. Relations to other methods are discussed, like "dissipative tunneling", RPA at finite temperature and generalizations of the "Static Path Approximation".
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arxiv:nucl-th/9703056
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Nuclear-polarizability corrections that go beyond unretarded-dipole approximation are calculated analytically for hydrogenic (atomic) S-states. These retardation corrections are evaluated numerically for deuterium and contribute -0.68 kHz, for a total polarization correction of 18.58(7) kHz. Our results are in agreement with one previous numerical calculation, and the retardation corrections completely account for the difference between two previous calculations. The uncertainty in the deuterium polarizability correction is substantially reduced. At the level of 0.01 kHz for deuterium, only three primary nuclear observables contribute: the electric polarizability, $\alpha_E$, the paramagnetic susceptibility, $\beta_M$, and the third Zemach moment, $< r^3 >_{(2)}$. Cartesian multipole decomposition of the virtual Compton amplitude and its concomitant gauge sum rules are used in the analysis.
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arxiv:nucl-th/9704032
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We report quantum Monte Carlo calculations of ground and low-lying excited states for nuclei with A \leq 7 using a realistic Hamiltonian containing the Argonne v18 two-nucleon and Urbana IX three-nucleon potentials. A detailed description of the Green's function Monte Carlo algorithm for systems with state-dependent potentials is given and a number of tests of its convergence and accuracy are performed. We find that the Hamiltonian being used results in ground states of both 6Li and 7Li that are stable against breakup into subclusters, but somewhat underbound compared to experiment. We also have results for 6He, 7He, and their isobaric analogs. The known excitation spectra of all these nuclei are reproduced reasonably well and we predict a number of excited states in 6He and 7He. We also present spin-polarized one-body and several different two-body density distributions. These are the first microscopic calculations that directly produce nuclear shell structure from realistic interactions that fit NN scattering data.
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arxiv:nucl-th/9705009
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We investigate thermodynamic properties and instability conditions in intermediate energy heavy ion reactions. We define locally thermodynamic variables, i.e. density, pressure and temperature, directly from the phase space distribution of a relativistic transport calculation. In particular, temperatures are determined by a fit to two covariant hot Fermi distributions thus taking into account possible anisotropic momentum configurations. We define instability independent from the nuclear matter spinodal by the criterion that the effective compressibility becomes negative. The method is applied to a semi-central Au on Au reaction at 600 MeV/nucleon. We investigate in particular the center of the participant and the spectator matter. In the latter we find a clear indication of instability with conditions of density and temperature that are consistent with experimental determinations.
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arxiv:nucl-th/9705023
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Nuclear-size corrections of order $(Z \alpha)^5$ and $(Z \alpha)^6$ to the S-state levels of hydrogenic atoms are considered. These nuclear-elastic contributions are somewhat smaller than the polarizability (nuclear-inelastic) corrections for deuterium, but are of comparable or larger size for the hydrogen case. For deuterium the (attractive) nonrelativistic $(Z \alpha)^5$ correction to the 2S-1S transition is 0.49 kHz, while the (repulsive) relativistic $(Z \alpha)^6$ contribution is -3.40 kHz. For the proton the corresponding corrections are 0.03 kHz and -0.61 kHz, respectively. The $(Z \alpha)^5$ contribution largely cancels the Coulomb-retardation part of the nuclear-polarization correction.
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arxiv:nucl-th/9705036
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A finite-dimensional matrix model for the nucleon-nucleon cross section operator is used to calculate the dispersive correction to nucleon-nucleus total cross sections, and the leading terms in its expansion in the number of inelastic transitions in the high-energy limit where the longitudnal momentum transfers can be ignored.
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arxiv:nucl-th/9705038
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An unified approach to the pseudo scalar meson ($\pi, \eta$, and $K$) photoproduction off nucleons are presented. It begins with the low energy QCD Lagrangian, and the resonances in the s- and u- channels are treated in the framework of the quark model The duality hypothesis is imposed to limit the number of the t-channel exchanges. The CGLN amplitudes for each reaction are evaluated, which include both proton and neutron targets. The important role by the S-wave resonances in the second resonance region is discussed, it is particularly important for the $K, \eta$ and $\eta^\prime$ photoproductions.
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arxiv:nucl-th/9706010
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A relativistic light front treatment of nuclei is developed by performing light front quantization for a chiral Lagrangian. The energy momentum tensor and the appropriate Hamiltonian are obtained. Three illustrations of the formalism are made. (1) Pion-nucleon scattering at tree level is shown to reproduce soft pion theorems. (2) The one boson exchange treatment of nucleon-nucleon scattering is developed and shown (by comparison with previous results of the equal time formulation) to lead to a reasonable description of nucleon-nucleon phase shifts. (3) The mean field approximation is applied to infinite nuclear matter, and the plus momentum distributions of that system are studied. The mesons are found to carry a significant fraction of the plus momentum, but are inaccessible to experiments.
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arxiv:nucl-th/9706028
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The rho-meson eletromagnetic form factors are calculated, both in covariant and light-front framework with constituintes quarks. The effect of the breakdown rotational symmetry for the one-body current operador in the null-plane is investigate by comparing calculations within ligth-front and covariant approaches.
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arxiv:nucl-th/9706032
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Thermal models are very useful in the understanding of particle production in general and especially in the case of strangeness. We summarize the assumptions which go into a thermal model calculation and which differ in the application of various groups. We compare the different results to each other. Using our own calculation we discuss the validity of the thermal model and the amount of strangeness equilibration at CERN-SPS energies. Finally the implications of the thermal analysis on the reaction dynamics are discussed.
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arxiv:nucl-th/9707020
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I discuss strangeness production in nucleus-nucleus reactions at ultrarelativistic energies (up to 200 AGeV). In these reactions matter may be created with densities and temperatures in the transition region between quark-gluon plasma (QGP) and hadron gas. Strange anti-baryon enhancement at 200 AGeV and probably even more so at 10 AGeV signals importance of interactions beyond hadron gas dynamics. The systematics of strangeness production indicates that energy and baryon density are key variables while the size of the production volume plays no visible role. Analysis of strangeness appears useful to explore thermalization, flow and the post-equilibrium stage in ultrarelativistic nucleus-nucleus collisions.
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arxiv:nucl-th/9707021
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The Toda criterion of the Gaussian curvature is applied to calculate analytically the transition energy from regular to chaotic motion in a schematic model describing the interaction between collective dipole and quadrupole modes in atomic nuclei.
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arxiv:nucl-th/9707024
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If textbook Lorentz invariance is actually a property of the equations describing a sector of the excitations of vacuum above some critical distance scale, several sectors of matter with different critical speeds in vacuum can coexist and an absolute rest frame (the vacuum rest frame) may exist without contradicting the apparent Lorentz invariance felt by "ordinary" particles (particles with critical speed in vacuum equal to $c$, the speed of light). Sectorial Lorentz invariance, reflected by the fact that all particles of a given dynamical sector have the same critical speed in vacuum, will then be an expression of a fundamental sectorial symmetry (e.g. preonic grand unification or extended supersymmetry) protecting a parameter of the equations of motion. Furthermore, the sectorial Lorentz symmetry may be only a low-energy limit, in the same way as the relation $\omega $ (frequency) = $c_s$ (speed of sound) $k$ (wave vector) holds for low-energy phonons in a crystal. In this context, phenomena such as the absence of Greisen-Zatsepin-Kuzmin cutoff for protons and nuclei and the stability of unstable particles (e.g. neutron, several nuclei...) at very high energy are basic properties of a wide class of noncausal models where local Lorentz invariance is broken introducing a fundamental length. Observable phenomena are expected at very short wavelength scales, even if Lorentz symmetry violation remains invisible to standard low-energy tests. We present a detailed discussion of the implications of Lorentz symmetry violation for very high-energy nuclear physics.
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arxiv:nucl-th/9708028
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The short range repulsion between nucleons is treated by a unitary correlation operator which shifts the nucleons away from each other whenever their uncorrelated positions are within the replusive core. By formulating the correlation as a transformation of the relative distance between particle pairs, general analytic expressions for the correlated wave functions and correlated operators are given. The decomposition of correlated operators into irreducible n-body operators is discussed. The one- and two-body-irreducible parts are worked out explicitly and the contribution of three-body correlations is estimated to check convergence. Ground state energies of nuclei up to mass number A=48 are calculated with a spin-isospin-dependent potential and single Slater determinants as uncorrelated states. They show that the deduced energy- and mass-number-independent correlated two-body Hamiltonian reproduces all "exact" many-body calculations surprisingly well.
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arxiv:nucl-th/9709038
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In a finite temperature Thomas-Fermi framework, we calculate density distributions of hot nuclei enclosed in a freeze-out volume of few times the normal nuclear volume and then construct the caloric curve, with and without inclusion of radial collective flow. In both cases, the calculated specific heats $C_v$ show a peaked structure signalling a liquid-gas phase transition. Without flow, the caloric curve indicates a continuous phase transition whereas with inclusion of flow, the transition is very sharp. In the latter case, the nucleus undergoes a shape change to a bubble from a diffuse sphere at the transition temperature.
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arxiv:nucl-th/9710018
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In terms of the exaxt angular momentum projection, properties of the three dimensional cranked HFB (3d-CHFB) states are analyzed quantitatively in the context of the relation between the signature of an intrinsic symmetry and the parity of angular momentum, (-1)^I. We found that the tilted states have favorable features to describe states involved with high-K quantum number and/or odd total angular momentum. This implies that 3d-CHFB can describe properly the backbending phenomena like a "t-band and g-band" crossing, which is suggested in N=106 isotopes.
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arxiv:nucl-th/9710028
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Large amplitude collective motion is investigated for a model pairing Hamiltonian containing an avoided level crossing. A classical theory of collective motion for the adiabatic limit is applied utilising either a time-dependent mean-field theory or a direct parametrisation of the time-dependent Schr\"odinger equation. A modified local harmonic equation is formulated to take account of the Nambu-Goldstone mode. It turns out that in some cases the system selects a diabatic path. Requantizing the collective Hamiltonian, a reasonable agreement with an exact calculation for the low-lying levels are obtained for both weak and strong pairing force. This improves on results of the conventional Born-Oppenheimer approximation.
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arxiv:nucl-th/9710037
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A Fortran program for the calculation of the ground state properties of axially deformed even-even nuclei in the relativistic framework is presented. In this relativistic mean field (RMF) approach a set of coupled differential equations namely the Dirac equation with potential terms for the nucleons and the Glein-Gordon type equations with sources for the meson and the electromagnetic fields are to be solved self-consistently. The well tested basis expansion method is used for this purpose. Accordingly a set of harmonic oscillator basis generated by an axially deformed potential are used in the expansion. The solution gives the nucleon spinors, the fields and level occupancies, which are used in the calculation of the ground state properties.
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arxiv:nucl-th/9710052
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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.
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arxiv:nucl-th/9711035
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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.
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arxiv:nucl-th/9711041
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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.
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arxiv:nucl-th/9712033
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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.
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arxiv:nucl-th/9712058
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Allowed $\beta^+$ branches of very proton-rich $fp$ shell $Tz=-2$ nuclei at the proton drip-line are calculated in the full fp valence space. The $\beta^+$ decay half-lives calculated with the standard quenching factor ($g^{eff}_{A}/g_{A}$)=0.74 are in good agreement with existing experimental data. Detailed branching Gamow-Teller strength are predicted but comparison with experiment is still difficult since, in most cases, spectroscopic information is not yet available.
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arxiv:nucl-th/9712065
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We comment on calculations of the width of the d' resonance within framework of quark shell models.
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arxiv:nucl-th/9712079
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Examples are given of the usefulness of electrons in interaction with nuclei for probing fundamental interactions and structure
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arxiv:nucl-th/9801021
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Possibility of observing the Mott momentum in the distribution of the deuterons produced in the process $p + n \to d + \gamma$, in the first stage of a nuclear reaction is presented. The correlation of a hard photon with a deuteron allows to select those deuterons produced at the beginning of a reaction.
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arxiv:nucl-th/9801032
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We present a very brief description of the Hartree-Fock method in nuclear structure physics, discuss the numerical methods used to solve the self-consistent equations, and analyze the precision and convergence properties of solutions. As an application we present results pertaining to quadrupole moments and single-particle quadrupole polarizations in superdeformed nuclei with A~60.
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arxiv:nucl-th/9801056
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Compton scattering data are sensitive to the existence of low-mass resonances reported by Tatischeff et al. We show that such states, with their reported properties, are excluded by previous Compton scattering experiments.
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arxiv:nucl-th/9801057
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The charge-current density and two-photon operators consistent with a single-particle semi-relativistic Hamiltonian are derived within a suitable functional derivative formalism which preserves gauge invariance. An application to electron scattering is presented and results are compared with a fully relativistic case and the non-relativistic cases corrected through fourth order in M^{-1}.
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arxiv:nucl-th/9801066
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By introducing electromagnetic formfactors in the spacelike region we extend an effective, gauge invariant Lagrangian model considering Born terms, baryon resonances up to 1.7 GeV and vector meson contributions (Rho, Omega) to calculate electroproduction of Pi-mesons. This model forms the basis for predictions of pion induced dilepton production on the nucleon. Therefore, the implemented formfactors are constructed in such a way that their analytic continuation into the timelike region is possible. It is shown that the seagull term and the N*(1520) resonance play a dominant role in the dilepton production.
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arxiv:nucl-th/9802010
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The sensitivity of the Sudbury Neutrino Observatory (SNO) to measure the shape of the recoil electron spectrum in the charged-current reaction of $^{8}$B solar neutrinos interacting with deuterium can be improved if the results of a $^{8}$Li beta-decay calibration experiment are included in the test. We calculate an improvement in sensitivity, under certain idealistic assumptions, of about a factor of 2, sufficient to resolve different neutrino-oscillation solutions to the solar-neutrino problem. We further examine the role of recoil and radiative corrections on both the $^{8}$B neutrino spectrum and the $^{8}$Li electron spectrum and conclude that the influence of these effects on the ratio of the two spectra as measured by SNO is very small.
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arxiv:nucl-th/9802078
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Pion dissociation in a medium of hot quark matter is studied. The decay width of pion is found to be large but finite at temperatures much higher than the so called critical temperature of chiral or deconfinement transition. Consequently, pions should coexist with quarks and gluons at such high temperatures. The result is in agreement with the lattice calculations. The implication of the above result in the study of Quark-Gluon plasma is discussed.
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arxiv:nucl-th/9803004
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Recent calculations of charge symmetry violation(CSV) in the valence quark distributions of the nucleon have revealed that the dominant symmetry breaking contribution comes from the mass associated with the spectator quark system.Assuming that the change in the spectator mass can be treated perturbatively, we derive a model independent expression for the shift in the parton distributions of the nucleon. This result is used to derive a relation between the charge and flavor asymmetric contributions to the valence quark distributions in the proton, and to calculate CSV contributions to the nucleon sea. The CSV contribution to the Gottfried sum rule is also estimated, and found to be small.
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arxiv:nucl-th/9803017
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The photodisintegration of the 7Li nucleus through the n6Li channel is considered on the basis of a potential two-cluster model. Intercluster-interaction potentials involve forbidden states and reproduce the phase shifts of low-energy elastic scattering that are obtained by the resonating-group method. The proposed model is shown to describe the total cross section for photodisintegration in the energy range under consideration.
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arxiv:nucl-th/9803023
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We analyse the SM97 partial wave amplitudes for nucleon--nucleon (NN) scattering to 2.5 GeV, in which resonance and meson production effects are evident for energies above pion production threshold. Our analyses are based upon boson exchange or quantum inversion potentials with which the sub-threshold data are fit perfectly. Above 300 MeV they are extrapolations, to which complex short ranged Gaussian potentials are added in the spirit of the optical models of nuclear physics and of diffraction models of high energy physics. The data to 2.5 GeV are all well fit. The energy dependences of these Gaussians are very smooth save for precise effects caused by the known $\Delta$ and N$^\star$ resonances. With this approach, we confirm that the geometrical implications of the profile function found from diffraction scattering are pertinent in the regime 300 MeV to 2.5 GeV and that the overwhelming part of meson production comes from the QCD sector of the nucleons when they have a separation of their centres of 1 to 1.2 fm. This analysis shows that the elastic NN scattering data above 300 MeV can be understood with a local potential operator as well as has the data below 300 MeV.
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arxiv:nucl-th/9803031
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Photodisintegration and radiative capture in the N2H, N3H, N3He, 2H2H, 2H3He, 2H4He, 3He3H, 4He3H, and 4He3He channels are studied on the basis of the corresponding two-cluster potential models. The astrophysical S factors at low energies are calculated. It is shown that various electromagnetic characteristics of light nuclei, including the Coulomb form factors at momenta of up to 4 F-1 can be studied using a single set of intercluster interactions containing forbidden states and consistent with the phase shifts of the cluster low-energy elastic scattering. The calculated inelastic form factors have a second maximum at 3-4 F-1, although it is lower than the experimental one. The orbital states are classified for the lightest cluster systems, and the phase shifts and intercluster potentials are separated on the basis of Young orbital schemes. It is first part of the review. Other parts will be published later.
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arxiv:nucl-th/9803039
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The work deals with one of the topics of collective motion. In the frame of Nuclear Fluid Dynamics, a model which portrays the nuclear matter as a quantum elastic body, the torus-like motions and their associated energies are computed using the thirteen moment approximation. The spin-dependent collective excitations, with toroidal electromagnetic structure, are studied by means of the Generalized Goldhaber-Teller model, with emphasize on the 1$^{-}$ spin-flip mode and its excitation in spherical nuclei by inelastic electron scattering. We discuss the importance of toroidal contributions in the inclusive electron scattering $(e, e')$ and exclusive coincidence electron scattering $(e, e'\gamma)$. In order to extract the toroidal multipole, we use the backscattering angles in the first mentioned reaction, and the separation of the longitudinal/transverse interference in the second case. The introduction of a quantity which accounts for the deviations from the Siegert theorem, shows the importance of toroidal quadrupole transitions at high-momentum transfer.
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arxiv:nucl-th/9803051
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We study elastic N$\alpha $ scattering and produce a quantitative correlation between the range of the effective potential and the energy of the system. This allows the identification of the waves and energies for which the scattering may be said to be peripheral. We then show that the corresponding phase shifts are sensitive to the tail of the NN potential, which is due to the exchange of two pions. However, the present uncertainties in the experimental phase shifts prevent the use of N$\alpha $ scattering to discriminate the existing models for the NN interaction.
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arxiv:nucl-th/9804063
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Few days ago V.D. Efros submitted a preprint to nucl-th containing criticisms of our recent research activity on bound and scattering states of A=3, 4 nucleons. As a consequence, we are forced to examine the essence of the controversy and of the comments contained in that preprint. These are the motivations of the present paper.
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arxiv:nucl-th/9804073
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The average transverse energy of nucleons and intermediate mass fragments observed in the heavy ion reaction Xe(50A MeV)+Sn shows the same linear increase as a function of their mass as observed in heavy ion collisions up to the highest ene rgies available today and fits well into the systematics. At higher energies this observation has been interpreted as a sign of a strong radial flow in an otherwise thermalized system. Investigating the reaction with Quantum Molecular dynamics simulations we find in between 50A MeV and 200A MeV a change in the reaction mechanism. At 50A MeV the apparent radial flow is merely caused by an in-plane flow and Coulomb repulsion. The average transverse fragment energy does not change in the course of the reaction and is equal to the initial fragment energy due to the Fermi motion. At 200A MeV, there are two kinds of fragments: those formed from spectator matte r and those from the center of the reaction. There the transverse energy is caused by the pr essure from the compressed nuclear matter. In both cases we observe a binary event stru cture, even in central collisions. This demonstrates as well the non thermal character of the reaction. The actual process which leads to multifragmentation is rather complex and is discussed in detail.
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arxiv:nucl-th/9805010
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We explore how nuclear modifications to the free nucleon structure functions (also known as shadowing) affect heavy quark production in collisions at different impact parameters. We assume that the nuclear modifications arise from a density dependent effect such as gluon recombination and are thus proportional to the local density. We calculate the dependence of charm and bottom quark production on impact parameter and show that density dependent modifications can lead to significant reductions in the heavy quark production cross sections in central relative to peripheral interactions.
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arxiv:nucl-th/9805027
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A systematic comparison of different isotopic temperatures with the thermodynamical temperature of a multifragment system is made on the basis of the Statistical Multifragmentation Model. It is demonstrated that isotopic temperatures are strongly affected by the secondary decays of hot primary fragments and the population of particle-stable excited states in final fragments. The He-Li temperatures, measured recently by the ALADIN group, are reproduced fairly well both as a function of excitation energy and bound charge. Our analysis confirms the anomaly in the nuclear caloric curve.
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arxiv:nucl-th/9805034
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A new criterion is developed which provides a check as to whether a chosen set of polarization observables is complete with respect to the determination of all independent $T$-matrix elements of a reaction of the type $a+b\to c+d+...$. As an illustrative example, this criterion is applied to the longitudinal observables of deuteron electrodisintegration.
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arxiv:nucl-th/9806017
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The properties of $\pi, \eta, K^+$ and $K^-$ mesons are studied in nuclear reactions from SIS to SPS energies within the covariant transport approach HSD in comparison to the experimental data. Whereas the pion, $\eta$ and kaon abundancies and spectra indicate little or vanishing selfe-nergies for these mesons in the medium, antikaons (as well as antiprotons) are found to experience strong attractive potentials in nucleus-nucleus collisions at SIS energies. However, even when including these potentials the $K^+$ and $K^-$ spectra at AGS energies are noticeably underestimated showing an experimental excess of strangeness that points towards a nonhadronic phase in these reactions. On the other hand the $K^+, K^-$ production at SPS energies is well described by the hadronic approach without incorporating any parton degrees of freedom.
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arxiv:nucl-th/9806051
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A Dyson-Schwinger-based model of pomeron exchange is employed to calculate diffractive rho-, phi- and J/psi-meson electroproduction cross sections. It is shown that the magnitude of the current-quark mass m_f of the quark and antiquark inside the produced vector meson determines the onset of the asymptotic-q^2 power-law behavior of the cross section, and how correlated quark-exchanges are included to provide a complete picture of the diffractive electroproduction of light vector mesons applicable over all energies and photon momenta q^2.
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arxiv:nucl-th/9806065
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The effects of the residual proton-neutron interactions on bandcrossing features are studied by means of shell model calculations for nucleons in a high-j intruder orbital. The presence of an odd-nucleon shifts the frequency of the alignment of two nucleons of the other kind along the axis of rotation. It is shown that the anomalous delayed crossing observed in nuclei with aligning neutrons and protons occupying the same intruder subshell can be partly attributed to these residual interactions.
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arxiv:nucl-th/9806094
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The formation of correlations due to collisions in an interacting nucleonic system is investigated shortly after a disturbance. Results from one-time kinetic equations are compared with the Kadanoff and Baym two-time equation with collisions included in second order Born approximation. A reasonable agreement is found for a proposed approximation of the memory effects by a finite duration of collisions. The formation of correlations and the build up time is calculated analytically for the high temperature and the low temperature limit. This translates into a time dependent increase of the effective temperature on time scales which interfere with standard fire ball scenarios of heavy ion collisions. The consequences of the formation of correlations on the two- particle interferometry are investigated and it is found that standard extracted lifetimes should be corrected downwards.
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arxiv:nucl-th/9807046
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We investigate a description of shape-mixing and shape-transitions using collective coordinates. To that end we apply a theory of adiabatic large-amplitude motion to a simplified nuclear shell-model, where the approximate results can be contrasted with exact diagonalisations. We find excellent agreement for different regimes, and contrast the results with those from a more standard calculation using a quadrupole constraint. We show that the method employed in this work selects diabatic (crossing) potential energy curves where these are appropriate, and discuss the implications for a microscopic study of shape coexistence.
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arxiv:nucl-th/9807078
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We investigate the reactions p n -> d omega and p n -> d phi close to threshold and at higher energies. Near threshold we calculate the S-wave amplitudes within the framework of the two-step model which is described by a triangle graph with pi-mesons in the intermediate state and find a ratio of the S-wave amplitudes squared of R =|A(phi)|^2/|A(omega)|^2 = (4-8) x 10^{-3}. Any significant enhancement of the experimental value of R(phi/omega) over this prediction can be interpreted as a possible contribution of the intrinsic s - anti s component in the nucleon-wave function. We present arguments that there is a strong resonance effect in the omega N channel close to threshold. At higher energies we calculate the differential cross sections of the reactions p n -> d omega, p n -> d phi and the ratio of the phi/omega yields within the framework of the quark-gluon string model. An irregular behavior of the phi/omega-ratio is found at s <= 12 GeV^2 due to the interference of the t- and u-channel contributions.
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arxiv:nucl-th/9808050
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We examine saturation properties of a quark-based picture of nuclear matter. Soliton matter consisting of nonlocal confining solitons is used to model nuclear matter. Each composite nucleon is described by a non-topological soliton as given by the Global Color Model. We apply techniques and concepts from the discription of crystal lattices. In particular, the Wigner-Seitz approximation is used to calculate the properties of the soliton lattice at the mean-field level. We focus on infinite nuclear matter at around standard nuclear matter density with the simplest one-parameter assumption for the gluon propagator. the saturation density and incompressibility are calculated as functions of the single parameter of the model
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arxiv:nucl-th/9808067
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Octet hyperon charge radii are calculated in a chiral constituent quark model including electromagnetic exchange currents between quarks. In impulse approximation one observes a decrease of the hyperon charge radii with increasing strangeness. This effect is reduced by exchange currents. Due to exchange currents, the charge radius of the negatively charged hyperons are close to the proton charge radius.
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arxiv:nucl-th/9809015
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Attention is drawn to the role played by the size of the system in the thermodynamic analysis of particle yields in relativistic heavy ion collisions at SIS energies. This manifests itself in the non-linear dependence of K+ and K- yields in $AA$ collisions at 1 -- 2 A.GeV on the number of participants. It is shown that this dependence can be quantitatively well described in terms of a thermal model with a canonical strangeness conservation. The measured particle multiplicity ratios (pi+/p, pi-/pi+, d/p, K+/pi+ and K+/K- but not eta/pi0) in central Au-Au and Ni-Ni collisions at 0.8 -- 2.0 A.GeV are also explained in the context of a thermal model with a common freeze-out temperature and chemical potential. Including the concept of collective flow a consistent picture of particle energy distributions is derived with the flow velocity being strongly impact-parameter dependent.
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arxiv:nucl-th/9809027
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The giant collective modes in asymmetric nuclear matter are investigated within a dynamic relaxation time approximation. We derive a coupled dispersion relation and show that two sources of coupling appear: (i) a coupling of isoscalar and isovector modes due to different mean-fields acting and (ii) an explicit new coupling in asymmetric matter due to collisional interaction. We show that the latter one is responsible for a new mode arising besides isovector and isoscalar modes.
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arxiv:nucl-th/9809035
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We investigate the nonrelativistic reduction of the Bethe-Salpeter amplitude for the deuteron electrodisintegration near threshold energies. To this end, two assumptions have been used in the calculations: 1) the static approximation and 2) the one iteration approximation. Within these assumptions it is possible to recover the nonrelativistic result including a systematic extension to relativistic corrections. We find that the so-called pair current term can be constructed from the $P$-wave contribution of the deuteron Bethe-Salpeter amplitude. The form factor that enters into the calculation of the pair current is constrained by the manifestly gauge independent matrix elements.
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arxiv:nucl-th/9809037
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Realistic solutions of the spinor-spinor Bethe-Salpeter equation for the deuteron with realistic interaction kernel including the exchange of pi, sigma, omega, rho, eta and delta mesons, are used to systematically investigate relativistic effects in inclusive quasi-elastic electron-deuteron scattering within the relativistic impulse approximation. Relativistic y-scaling is considered by generalising the non relativistic scaling function to the relativistic case, and it is shown that y-scaling does occur in the usual relativistic scaling variable resulting from the energy conservation in the instant form of dynamics. The present approach of y-scaling is fully covariant, with the deuteron being described by eight components, viz. the 3S_1^{++}, 3S_1^{--}, 3D_1^{++}, 3D_1^{--}, 3P_1^{+-}, 3P_1^{-+}, 1P_1^{+-}, 1P_1^{-+} waves. It is demonstrated that if the negative relative energy states 1P_1, 3P_1 are disregarded, the concept of covariant momentum distributions N(p_0,p), with p_0=M_D/2-\sqrt{p^2+m^2}, can be introduced, and that calculations of lectro-disintegration cross section in terms of these distributions agree within few percents with the exact calculations which include the 1P_1, 3P_1 states, provided the nucleon three momentum |p|\<= 1 GeV/c; in this momentum range, the asymptotic relativistic scaling function is shown to coincide with the longitudinal covariant momentum distribution.
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arxiv:nucl-th/9809040
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Signature effects observed in rotational bands are a consequence of an inherent D2-symmetry. This symmetry is naturally broken by the mean field cranking approximation when a tilted (non-principal) axis orientation of the nuclear spin becomes stable. The possible tunneling forth and back between the two symmetry-related minima in the double-humped potential-energy surface appears as a typical bifurcation of the rotational band. We describe this many-body process in which all nucleons participate by diagonalizing the nuclear Hamiltonian within a selected set of tilted and non-tilted cranking quasiparticle states. This microscopic approach is able to restore the broken D2 symmetry and reproduce the quantum fluctuations between symmetry- related HFB states which emerge as splitting of the band energies and in parallel staggering in intraband M1 transitions.
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arxiv:nucl-th/9809045
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We have made a needed correction to our earlier paper (nucl-th/9511002), which contains a sign error. With this correction, the weak parity-violating pion-nucleon coupling is about 3 x 10^(-7).
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arxiv:nucl-th/9809064
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We have calculated the Gamow-Teller strength distributions for the ground states and first excited states in 55Co and 56Ni. These calculations have been performed by shell model diagonalization in the pf shell using the KB3 interaction. The Gamow-Teller distributions are used to calculate the electron capture rates for typical presupernova conditions. Our 55Co rate is noticeably smaller than the presently adopted rate as it is dominated by weak low-lying transitions rather than the strong Gamow-Teller (GT) resonance which is located at a higher excitation energy in the daughter than usually parametrized. Although our 56Ni rate agrees with the presently adopted rate, we do not confirm the conventional parametrization of the GT centroid. Our results support general trends suggested on the basis of shell model Monte Carlo calculations.
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arxiv:nucl-th/9809081
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The value of the $V_{ud}$ matrix element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix can be derived from nuclear superallowed beta decays, neutron decay, and pion beta decay. We survey current world data for all three. Today, the most precise value of $V_{ud}$ comes from the nuclear decays; however, the precision is limited not by experimental error but by the estimated uncertainty in theoretical corrections. The neutron data are approximately a factor of four poorer in precision but this could change dramatically in the near future as planned experiments come to fruition. The nuclear result (and the most recent of the neutron decay results) differ at the 98% confidence level from the unitarity condition for the CKM matrix. We examine the reliability of the small calculated corrections that have been applied to the data, and assess the likelihood of even higher quality nuclear data becoming available to confirm or deny the discrepancy. Some of the required experiments depend upon the availability of intense radioactive beams. Others are possible today.
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arxiv:nucl-th/9809087
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The s-wave meson-nucleon interaction in the S=-1 sector is studied by means of a coupled-channel Lippmann Schwinger equation, using the lowest order chiral Lagrangian and a cut off to regularize the loop integrals. The position and width of the Lambda(1405) resonance and the K^- p scattering cross sections at low energies are well reproduced. 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. The model is applied to calculate the in-medium K^- self-energy to which we add a small p-wave piece resulting from the coupling to hyperon particle-nucleon hole excitations. The K^- feels an attraction of about -100 MeV at normal nuclear density. The Lambda(1405) resonance shifts to energies above the $K^-p$ threshold and ends up dissolving as density increases. It remains to be seen how these effects persist when the dressing of the Kbar and the pi mesons is incorporated self-consistently in the calculation.
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arxiv:nucl-th/9810014
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The light cone QCD sum rules are derived for $\omega NN$ vector and tensor couplings simultaneously. The vacuum gluon field contribution is taken into account. Our results are $g_\omega =(18\pm 8), \kappa_\omega=(0.8\pm 0.4)$.
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arxiv:nucl-th/9810031
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Thermal models are commonly used to interpret heavy-ion data on particle yields and spectra and to extract the conditions of chemical and thermal freeze-out in heavy-ion collisions. I discuss the usefulness and limitations of such thermal model analyses and review the experimental and theoretical evidence for thermalization in nuclear collisions. The crucial role of correlating strangeness production data with single particle spectra and two-particle correlation measurements is pointed out. A consistent dynamical picture for the heavy-ion data from the CERN SPS involves an initial prehadronic stage with deconfined color and with an appreciable isotropic pressure component. This requires an early onset of thermalization.
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arxiv:nucl-th/9810056
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We reexamine the production of J/Psi and other charmonium states for a variety of target-projectile choices at the SPS, in particular for the interesting comparison between S+U at 200 GeV/c and Pb+Pb at 158 GeV/c as observed in the experiments NA38 and NA50 respectively. The result is a description of the NA38 and NA50 data in terms of a conventional, quasi-hadronic picture. The apparently anomalous suppression found in the most massive Pb+Pb system arises in the present simulation from three sources: destruction in the initial nucleon-nucleon cascade phase, use of coupled channels to exploit the larger breakup in the less bound Chi and Psi' states, and comover interaction in the final low energy phase.
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arxiv:nucl-th/9810064
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We discuss the relation between the two nucleon Bethe-Salpeter amplitude and the light front wave functions. Both approaches provide a covariant description for the deuteron bound state and the two nucleon scattering state. A comparison is done for the spin-orbit functions as well explicit integrals are given on the basis of the Nakanishi integral representation method.
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arxiv:nucl-th/9811022
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We discuss renormalization of the non-relativistic three-body problem with short-range forces. The problem is non-perturbative at momenta of the order of the inverse of the two-body scattering length. An infinite number of graphs must be summed, which leads to a cutoff dependence that does not appear in any order in perturbation theory. We argue that this cutoff dependence can be absorbed in one local three-body force counterterm and compute the running of the three-body force with the cutoff. This allows a calculation of the scattering of a particle and the two-particle bound state if the corresponding scattering length is used as input. We also obtain a model-independent relation between binding energy of a shallow three-body bound state and this scattering length. We comment on the power counting that organizes higher-order corrections and on relevance of this result for the effective field theory program in nuclear and molecular physics.
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arxiv:nucl-th/9811046
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The physics of nuclear reactions in stellar plasma is reviewed with special emphasis on the importance of the velocity distribution of ions. Then the properties (density and temperature) of the weak-coupled solar plasma are analysed, showing that the ion velocities should deviate from the Maxwellian distribution and could be better described by a weakly-nonexstensive (|q-1|<0.02) Tsallis' distribution. We discuss concrete physical frameworks for calculating this deviation: the introduction of higher-order corrections to the diffusion and friction coefficients in the Fokker-Plank equation, the influence of the electric-microfield stochastic distribution on the particle dynamics, a velocity correlation function with long-time memory arising from the coupling of the collective and individual degrees of freedom. Finally, we study the effects of such deviations on stellar nuclear rates, on the solar neutrino fluxes, and on the pp neutrino energy spectrum, and analyse the consequences for the solar neutrino problem.
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arxiv:nucl-th/9811081
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A linked cluster expansion for the distorted one-body mixed density matrix is obtained within the Glauber multiple scattering theory with correlated wave functions. The nuclear transparency for 16O is calculated using realistic central and non-central correlations. The convergence of the expansion is investigated in the case of 4He for which the transparency and the distorted momentum distributions are calculated to all order in the correlations using a variational wave function obtained from realistic NN interactions. The important role played by non central correlations is illustrated.
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arxiv:nucl-th/9811102
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Brueckner-Hartree-Fock calculations are performed for nuclear matter with an exact treatment of the Pauli exclusion operator in the Bethe-Goldstone equation. The differences in the calculated binding energy, compared to the angle-average approximation, which is commonly used, are non-negligible. These difference exhibits a specific density dependence, which shifts the calculated saturation point towards smaller densities. This effect is observed for various versions of modern models for the NN interaction.
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arxiv:nucl-th/9812011
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We study phase transitions of small two dimensional Lennard Jones drops via microcanonical molecular dynamics in a broad energy range. We found that the caloric curve can be extended to high energies to comprehend high evaporation rates and highly non-equilibrium phenomena such as multifragmentation. Multifragmentation appears as a constant temperature region in the caloric curve like the solid-liquid phase transition.
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arxiv:nucl-th/9812015
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The constraints imposed by chiral symmetry on hadron correlation functions in nuclear medium are discussed. It is shown that these constraints imply some structure of the in-medium hadron correlators, lead to the cancellation of the order $\rho m_\pi$ term in the in-medium nucleon correlator and result in the effect of mixing of the chiral partners correlators, reflecting the phenomena of partial restoration of chiral symmetry. The different scenarios of such restorations are briefly discussed.
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arxiv:nucl-th/9812017
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A distinct isotopic effect in phi photoproduction at 2-5 GeV region is identified by examining the production amplitudes due to Pomeron-exchange and meson-exchange mechanisms. This effect is mainly caused by the pi-eta interference constrained by SU(3) symmetry and the isotopic structure of the gamma NN coupling in the direct phi-radiation amplitude. It can be tested experimentally by measuring differences in the polarization observables between the gamma-p and gamma-n reactions.
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arxiv:nucl-th/9812074
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