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 Schrödinger 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.     

Pauli blocking in degenerate plasmas and the separable potential approach

The Mott effect describes the dissolution of bound states in a dense partially ionized plasma. It occurs when the ionization potential depression, owing to effects of correlation and degeneracy, compensates the binding energy of the bound state. At high densities and moderate temperatures, the Pauli blocking becomes important and influences significantly the degree of ionization in the region of degenerate plasmas. A quantum statistical approach is used where the total density is decomposed in an uncorrelated, “free” part and correlations, as a consequence of the cluster decomposition of the self‐energy. The contribution of correlations to the total density is given by bound states and continuum correlations. Exact solutions for a separable potential are compared to perturbation theory and numerical solutions of the in‐medium Schrödinger equation. The in‐medium scattering phase shifts are evaluated, and the role of continuum correlations is discussed. The Pauli blocking of bound states and the density of states are considered for warm dense matter conditions.     

Pauli blocking and Fermi motion effects in ion-ion collisions

A geometrical model for Pauli blocking and Fermi motion effects in ion-ion collisions is presented. The results, given as effective nucleon-nucleon total cross sections, incicate that the Pauli blocking reduces the nucleon-nucleon cross section in the ion-ion environment by a larger amount than previously estimated.     

Pauli blocking effect on Efimov states near a Feshbach resonance

In this Letter we study the effect of Pauli blocking on Efimov states in a quantum Fermi gas and illustrate that the universal Efimov potential is altered at large distances. We obtain the universal spectrum flow of Efimov trimers when the Fermi density is varied and further consider the effect of scattering of trimers by the Fermi sea. We argue that the universal flow is robust against fluctuating particle-hole pairs that result in an infrared catastrophe in impurity problems.     

The Coulomb integrals and the diffraction model of transfer reactions

The resonating group interaction of three clusters, in the single channel no-distortion approximation, is split into a leading part and a residual part. In norm kernel eigenstate representation, the leading part exhibits a peculiar, fish bone like symmetry. An off-shell transformation, which leads to an energy-independent interaction, also reduces the strength of the three-body Pauli potential. The smallness of this potential is related to the possibility of interpreting cluster relative motion wave functions as probability density amplitudes. Neglecting all residual interactions and introducing, instead, fitting parameters into the two-cluster direct interactions leads to a three-cluster optical model. In this model the on-shell behaviour of two-cluster interactions is determined by experimental data, while their off-shell behaviour, as well as the three-cluster Pauli potential, are determined by the Pauli principle.     

Nucleon-nucleon correlations with quark degrees of freedom

A dynamical equation of two nucleons in a nucleus is formulated in the nonrelativistic quark model including Pauli blocking due to the other nucleons. This equation is solved with a model wave function containing the possiblity of six-quark bags with different radii. It is shown that the Pauli blocking effect is emphasized by the non-nucleonic degrees of freedom represented by six-quark bags. The modification of the quark momentum distribution for correlated nucleons is calculated and probabilities of non-NN components in nuclei are estimated.     

Particle-hole state densities with energy constraints and exact Pauli exclusion effect

A formula is derived for the density of particle-hole states in the equidistant spacing model.The effect of the Pauli exclusion principle is exactly taken into acount.The pairing effect as well as two energy constraints are involved.The formula is suited for calculating.Comparisons of the results imply that the Pauli effect and the pairing effect play an important role in particle-hole state density.     

Experimental determination of in-medium cluster binding energies and Mott points in nuclear matter

In-medium binding energies and Mott points for d, t, 3He and α clusters in low-density nuclear matter have been determined at specific combinations of temperature and density in low-density nuclear matter produced in collisions of 47A MeV 40Ar and 64Zn projectiles with 112Sn and 124Sn target nuclei. The experimentally derived values of the in-medium modified binding energies are in good agreement with recent theoretical predictions based upon the implementation of Pauli blocking effects in a quantum statistical approach.     

Improvements on the imaginary part of a non-empirical model potential for electron scattering (30 to 10000 eV energies)

The non-empirical model proposed by Staszewska et al. in 1983 for the imaginary part of electron scattering optical potential is revised. Electron indistinguishability in Pauli blocking conditions and an screening correction are proposed. Results for He, Ne and Ar favourably compare with previous model and experimental values, for inelastic processes.     

Neutrino nucleus cross sections for low energy neutrinos at SNS facilities

We calculate the neutrino nucleus cross sections for charged lepton production relevant for the experiments proposed with the stopped muon neutrinos using neutron spallation source facility. The calculations are done in local density approximation taking into account Pauli blocking, Fermi motion effects and renormalization of weak transition strengths in the nuclear medium. The effect of Coulomb distortion of the lepton produced in charge current reactions is taken into account by using the Fermi function as well as in a model where an effective momentum has been used for the lepton moving in the local Coulomb field of the final nucleus. The numerical results for the neutrino nucleus total cross sections averaged over Michel spectrum are presented for various nuclei.     

Nuclear level density with fixed exciton number

An expression for the nuclear level density has been obtained for fixed number of particlesp and holesh taking into account the energy dependence of the single-particle state density for a gas model of noninteracting particles. The applicability of the equidistant spacing model (g=const.) is analyzed for the casesp?h andp? h?1. The possibility of factorization of the angular momentum dependence is studied provided g≠const. A semi-classical expression for the dependence of the single-particle density on angular momentum projection has been obtained without specifying the nuclear potential. Them-dependence ofg(?, m) is shown to be close to a Gaussian for the infinite square well potential. A simple expression which takes into account the effect of the Pauli exclusion principle is proposed for the angular momentum dispersion of the level density distribution.     

Collisions in zero temperature Fermi gases

We examine the collisional behavior of two-component Fermi gases released at zero temperature from a harmonic trap. Using a phase-space formalism to calculate the collision rate during expansion, we find that Pauli blocking plays only a minor role for momentum changing collisions. As a result, for a large scattering cross section, Pauli blocking will not prevent the gas from entering the collisionally hydrodynamic regime. In contrast to the bosonic case, hydrodynamic expansion at very low temperatures is therefore not evidence for fermionic superfluidity.     

Effective nuclear interaction: Dirac versus conventional approach

The effective interaction in nuclear matter (G-matrix) is calculated, in the relativistic (Dirac-Brueckner-Hartree-Fock) as well as in the conventional Brueckner-Hartree-Fock approach. Starting point is a nucleon-nucleon potential which, in addition to single-meson exchange, contains delta-isobar box diagrams with ππ- and πϱ-exchange, leading to Pauli blocking and dispersive effects. The implications for nuclear matter binding and Landau parameters are investigated.     

Particle-hole state densities for statistical multi-step compound reactions

An analytical relation is derived for the density of particle-hole bound states applying the equidistant-spacing approximation and the Darwin-Fowler statistical method. The Pauli exclusion principle as well as the finite depth of the potential well are taken into account. The set of densities needed for calculations of multi-step compound reactions is completed by deriving the densities of accessible final states for escape and damping.     

Coupled channel study of kaonic 12C

A coupled channel formalism is used to study the role of the Λ(1405) for kaonic ¹²C in a non-static way. Medium corrections are calculated in a microscopic fashion, closely related to a Brueckner type of “independent pair approximation”. Nucleon and kaon binding effects (the latter in a rudimentary self-consistent way) and the Pauli blocking effect are examined and some of the widely used approximations (Fermi gas and local density, closure approximation) are put to trial. Fair agreement with experiment can be obtained without a free parameter, but it is shown to depend sensitively on the input elementary (sub-threshold) scattering amplitude.     

A simple model for short-range correlations in nuclear matter

It is shown that Pauli blocking and short-range correlation effects, which strongly renormalize the bare nucleon-nucleon interaction in the medium, can be summarized in a correlation operator which has an extremely simple structure. The use of such a simple correlation operator leads to a form of Brueckner's reaction-matrix interaction which is very convenient for applications. The effective interaction introduced by the Jülich-Stony Brook group and extensively used in the study of the spin-isospin excitation modes in nuclei is derived from a meson exchange potential.     

Description of nucleon-nucleus scattering in the Dirac-Brueckner method

Elastic scattering of protons from nuclei is studied based on the Dirac-Brueckner approach. Effective N-N interactions in the nuclear medium are obtained by solving the relativistic Brueckner-Bethe-Goldstone equation in infinite nuclear matter. Relativistic optical potentials for p-⁴⁰Ca scattering at 200 MeV are calculated in the improved local density approximation. It is found that medium effects other than Pauli blocking reduce the strengths of scalar and vector potentials very much. Differential cross section and spin observables are calculated and compared with experimental data.     

Pauli blocking potential applied to heavy-ion fusion reactions

In this study, the Pauli blocking potential between two colliding nuclei in the density overlapping region is applied to describe the heavy nuclei fusion process. Inspired by the Pauli blocking effect in the \begin{document}$ \alpha $\end{document}-decay of heavy nuclei, the Pauli blocking potential of single nucleon from the surrounding matter is obtained. In fusion reactions with strong density overlap, the Pauli blocking potential between the projectile and target can be constructed using a single folding model. By considering this potential, the double folding model with a new parameter set is employed to analyze the fusion processes of 95 systems. A wider Coulomb barrier and shallower potential pocket are formed in the inner part of the potential between the two colliding nuclei, compared to that calculated using the Akyüz-Winther potential. The fusion hindrance phenomena at deep sub-barrier energies are described well for fusion systems \begin{document}$ ^{16} $\end{document}O + \begin{document}$ ^{208} $\end{document}Pb and \begin{document}$ ^{58} $\end{document}Ni + \begin{document}$ ^{58} $\end{document}Ni.     

Quantum kinetic equation for nonequilibrium dense systems

Using the density matrix method in the form developed by Zubarev, equations of motion for nonequilibrium quantum systems with continuous short range interactions are derived which describe kinetic and hydrodynamic processes in a consistent way. The T-matrix as well as the two-particle density matrix determining the nonequilibrium collision integral are obtained in the ladder approximation including the Hartree-Fock corrections and the Pauli blocking for intermediate states. It is shown that in this approximation the total energy is conserved. The developed approach to the kinetic theory of dense quantum systems is able to reproduce the virial corrections consistent with the generalized Beth-Uhlenbeck approximation in equilibrium. The contribution of many-particle correlations to the drift term in the quantum kinetic equation for dense systems is discussed.     

Charm Hadrons in Dense Matter

The properties of the D and D _s charmed mesons in normal nuclear matter density are studied within a coupled channel approach using a t-channel vector-meson exchange mechanism as driving force. The in-medium scattering amplitudes are obtained by solving the Lippmann?CSchwinger equation including Pauli blocking effects and medium self-energies in a self-consistent way.