Off-shell effects on particle production

We investigate the observable effects of off-shell propagation of nucleons in heavy-ion collisions at SIS energies. Within a semi-classical BUU transport model we find a strong enhancement of subthreshold particle production when off-shell nucleons are propagated.Comment: 11 pages, 3 figure

Spectral Function of Quarks in Quark Matter

We investigate the spectral function of light quarks in infinite quark matter using a simple, albeit self-consistent model. The interactions between the quarks are described by the SU(2) Nambu--Jona-Lasinio model. Currently mean field effects are neglected and all calculations are performed in the chirally restored phase at zero temperature. Relations between correlation functions and collision rates are used to calculate the spectral function in an iterative process.Comment: final version, published in PRC; 15 pages, RevTeX

Transport Theoretical Approach to the Nucleon Spectral Function in Nuclear Matter

The nucleon spectral function in infinite nuclear matter is calculated in a quantum transport theoretical approach. Exploiting the known relation between collision rates and correlation functions the spectral function is derived self-consistently. By re-inserting the spectral functions into the collision integrals the description of hard processes from the high-momentum components of wave functions and interactions is improved iteratively until convergence is achieved. The momentum and energy distributions and the nuclear matter occupation probabilities are in very good agreement with the results obtained from many-body theory.Comment: minor changes in the text, additional curves in fig.

Baryon flow at SIS energies

We calculate the baryon flow $$ in the energy range from .25 to $\le 2.5 AGeV$ in a relativistic transport model for $Ni+Ni$ and $Au+Au$ collisions employing various models for the baryon self energies. We find that to describe the flow data of the FOPI Collaboration the strength of the vector potential has to be reduced at high relative momentum or at high density such that the Schr\"odinger- equivalent potential at normal nuclear density decreases above 1 GeV relative kinetic energy and approaches zero above 2 GeV.Comment: 20 pages, LATEX, 7 PostScript figure

Towards a fully self-consistent spectral function of the nucleon in nuclear matter

We present a calculation of nuclear matter which goes beyond the usual quasi-particle approximation in that it includes part of the off-shell dependence of the self-energy in the self-consistent solution of the single-particle spectrum. The spectral function is separated in contributions for energies above and below the chemical potential. For holes we approximate the spectral function for energies below the chemical potential by a $\delta$-function at the quasi-particle peak and retain the standard form for energies above the chemical potential. For particles a similar procedure is followed. The approximated spectral function is consistently used at all levels of the calculation. Results for a model calculation are presented, the main conclusion is that although several observables are affected by the inclusion of the continuum contributions the physical consistency of the model does not improve with the improved self-consistency of the solution method. This in contrast to expectations based on the crucial role of self-consistency in the proofs of conservation laws.Comment: 26 pages Revtex with 4 figures, submitted to Phys. Rev.

Space-time versus particle-hole symmetry in quantum Enskog equations

The non-local scattering-in and -out integrals of the Enskog equation have reversed displacements of colliding particles reflecting that the -in and -out processes are conjugated by the space and time inversions. Generalisations of the Enskog equation to Fermi liquid systems are hindered by a request of the particle-hole symmetry which contradicts the reversed displacements. We resolve this problem with the help of the optical theorem. It is found that space-time and particle-hole symmetry can only be fulfilled simultaneously for the Bruckner-type of internal Pauli-blocking while the Feynman-Galitskii form allows only for particle-hole symmetry but not for space-time symmetry due to a stimulated emission of Bosons

Quasiparticle transport equation with collision delay. II. Microscopic Theory

For a system of non-interacting electrons scattered by neutral impurities, we derive a modified Boltzmann equation that includes quasiparticle and virial corrections. We start from quasiclassical transport equation for non-equilibrium Green's functions and apply limit of small scattering rates. Resulting transport equation for quasiparticles has gradient corrections to scattering integrals. These gradient corrections are rearranged into a form characteristic for virial corrections

In-medium relativistic kinetic theory and nucleon-meson systems

Within the $\sigma-\omega$ model of coupled nucleon-meson systems, a generalized relativistic Lenard--Balescu--equation is presented resulting from a relativistic random phase approximation (RRPA). This provides a systematic derivation of relativistic transport equations in the frame of nonequilibrium Green's function technique including medium effects as well as flucuation effects. It contains all possible processes due to one meson exchange and special attention is kept to the off--shell character of the particles. As a new feature of many particle effects, processes are possible which can be interpreted as particle creation and annihilation due to in-medium one meson exchange. In-medium cross sections are obtained from the generalized derivation of collision integrals, which possess complete crossing symmetries.Comment: See nucl-th/9310032 for revised version which the authors incompetently resubmitted rather than correctly replacing thi

On the Lorentz structure of the symmetry energy

We investigate in detail the density dependence of the symmetry energy in a relativistic description by decomposing the iso-vector mean field into contributions with different Lorentz covariant properties. We find important effects of the iso-vector, scalar channel (i.e. $\delta$-meson like) on the high density behavior of the symmetry energy. Applications to static properties of finite nuclei and to dynamic situations of heavy ion collisions are explored and related to each other. The nuclear structure studies show only moderate effects originating from the virtual $\delta$ meson. At variance, in heavy ion collisions one finds important contributions on the reaction dynamics arising from the different Lorentz structure of the high density symmetry energy when a scalar iso-vector $\delta$ field is introduced. Particularly interesting is the related neutron/proton effective mass splitting for nucleon transport effects and for resonance and particle production around the threshold. We show that the $\delta$-like channel turns out to be essential for the production of pions, when comparing with experimental data, in particular for high momentum selections.Comment: 30 pages, 12 figures (.eps

Quantum Tunneling in the Wigner Representation

Time dependence for barrier penetration is considered in the phase space. An asymptotic phase-space propagator for nonrelativistic scattering on a one - dimensional barrier is constructed. The propagator has a form universal for various initial state preparations and local potential barriers. It is manifestly causal and includes time-lag effects and quantum spreading. Specific features of quantum dynamics which disappear in the standard semi-classical approximation are revealed. The propagator may be applied to calculation of the final momentum and coordinate distributions, for particles transmitted through or reflected from the potential barrier, as well as for elucidating the tunneling time problem.Comment: 18 pages, LATEX, no figure