Rudi Malfliet

QUANTUM TRANSPORT-THEORY OF NUCLEAR-MATTER

Quantum kinetic equations are derived using the Keldysh Greens function formalism to describe non-equilibrium processes in nuclear matter and nucleus-nucleus collisions. A general transport equation is proposed which includes energy spreading effects. We discuss a number of specific kinetic equations which are the non-equilibrium versions of well-known many-body theories for equilibrated nuclear matter. Special emphasis is put on Brueckner-type approaches and the problem of complying with conservation laws. Finally we consider the relativistic extension of the formalism.

Semi-classical approximations to heavy ion scattering based on the Feynman path-integral method

Abstract A semi-classical theory, derived from the Feynman path-integral formalism by applying the saddle point method, is formulated for elastic and inelastic heavy ion reactions. This theory is a natural extension of earlier semi-classical methods in the sense that classical, real, trajectories are extended to complex ones by an analytic continuation of Hamiltons equations. It describes properly the role played by the complex interaction and the resulting absorptive, refractive and diffractive phenomena. The connection with the WKB-approximation is discussed. A comparison between the results of three types of calculation is made: exact (quantum mechanical), semi-classical and the earlier semi-classical approach based on real trajectories. This shows the quantitative power of the semi-classical method presented here, not only for the elastic and inelastic cross sections but it also reproduces the quantum mechanical phase shifts, reflection coefficients and excitation coefficients in quite some detail, contrary to the earlier semi-classical calculations.

A relativistic quantum kinetic equation for nucleus-nucleus collisions

A relativistic quantum kinetic equation is derived corresponding to the non-equilibrium extension of the Dirac-Brueckner approach for nuclear matter. The equation is of the VUU-type with a self-consistent mean field and collision term.

Two-body collisions and mean-field theory: The Brueckner-Boltzmann equation

Abstract Starting from the BBGKY hierarchy of density matrices, a quantum mechanical Boltzmann equation, including a mean field, is derived. Both the mean field, which is of the well-known Brueckner-Hartree-Fock form, as well as the collision term are expressed in terms of the self-consistent Brueckner G-matrix. The relation with the generalized Boltzmann equation of Kadanoff and Baym is discussed. It is shown that the usual quantum mechanical theories like TDHF and Uehling-Uhlenbeck appear as limiting cases.

ANALYTICAL TREATMENT OF HIGH-ENERGY NUCLEUS NUCLEUS COLLISIONS

Abstract We review an analytical study of high-energy nucleus-nucleus collisions based on Boltzmanns kinetic theory of gases. In the first part of the paper, we do not take effects of the nuclear mean field into account. This turns out to be appropriate for particle inclusive production, as the good agreement of the theory with a large variety of inclusive experimental data demonstrates. As soon as physical observables extracted from measurements on an event per event basis are considered, the nuclear potential plays a decisive role. To account for this fact, we extend the theory by including the nuclear mean field in the Boltzmann equation. The results obtained are in qualitative agreement with experimental exclusive observables such as the sideward kinetic energy flow angle and the average transverse momentum, despite the absence of strong compression of nuclear matter in the theory presented.

The single-particle interaction in nuclear matter via the relativistic Dirac-Brueckner approach

Within the relativistic Dirac-Brueckner approach and starting from a one-boson-exchange interaction, the nucleon selfenergy is calculated above the nuclear-matter Fermi sea. The effects of Pauli blocking and energy dispersion are studied. At low energy we see a dominance of the Pauli blocking whereas at nucleon energies up to 250 MeV the dispersive effect still has a very large influence on the single-particle interaction. From the selfenergy a Schrodinger optical potential is deduced, for which the DB results nicely agree with empirical values. The density dependence of this optical potential compares well with earlier calculations.

Trinucleon bound state properties and form factors with the B.K.R. potential

The triton binding energy, S′ - and D-state probabilities are determined using the B.K.R. potential. Neglecting mesonic corrections, the charge and magnetic form factors are computed for 3H and 3He. They show a diffraction minimum at q2 = 14.4 fm−2.

Self-consistent inclusion of pion polarisation in the relativistic Dirac-Brueckner approach to nuclear matter

We investigate the influence of pion polarisation effects in the Dirac-Brueckner approach. The pion polarisation is included preserving the self-consistency of the DB approach. Results for single-particle properties, equation of state, and total effective cross sections in symmetric nuclear matter are presented. Also, we calculated the pion condensation threshold.

Compressibility of nuclei in relativistic mean field theory

Abstract Using the relativistic Hartree approximation in the σ-ω model we study the isoscalar giant monopole resonance. It is shown that the ISGMR of lighter nuclei has non-negligible anharmonic terms. The compressibility of nuclear matter is determined using a leptodermous expansion.

Towards a relativistic self-consistent nucleon spectral function in the nuclear medium

Abstract An iterative procedure is developed for solving the Schwinger-Dyson equation for the coupled nucleon and pion propagators for the case when vertex corrections are neglected. The presence of ghost poles in the dressed propagators is avoided by using explicitly only the imaginary part of the propagators, eliminating the real part through a dispersion relation.