Skyrme Potential Research Articles

Neutrino scattering rates in the presence of hyperons from a Skyrme model in the RPA approximation

The contribution of Λ-hyperons to neutrino scattering rates is calculated in the random phase approximation in a model where the interaction is described by a Skyrme potential. Finite temperature and neutrino trapping are taken into account in view of applications to the deleptonization stage of protoneutron star cooling. The hyperons can remove the problem of ferromagnetic instability common to (nearly) all Skyrme parametrizations of the nucleon-nucleon interaction. As a consequence, there is not any longer a pole at the transition in the neutrino-baryon cross-section. However there still remains an enhancement in this region. In the absence of ferromagnetism the mean free path in npΛ matter is reduced compared to its value in np matter as a consequence of the presence of this additional degree of freedom. At high density the results are very sensitive to the choice of the Λ-Λ interaction.

NEUTRON MATTER PROPERTIES USING GENERALIZED SKYRME FORCE

The generalized Skyrme potential is used to calculate the properties of neutron matter in the form of the Thomas–Fermi model. The binding energy per particle, spin symmetry energy, free energy, pressure, entropy, sound velocity and magnetic susceptibility are calculated as a function of density ρ. The results are comparable with those obtained by Friedman and Pandharipande, who used the Urbana v14 potential plus an effective repulsive three-body force.

Equation of state of hot polarized nuclear matter using the generalized Skyrme interaction

We used the generalized Skyrme potential to study the equation of state of polarized nuclear matter in the frame of the Thomas-Fermi model. The critical temperature of the liquid-gas phase transition is found to be ${T}_{c}=16.2\mathrm{MeV}.$ This critical temperature was found to decease with the asymmetry, spin, and spin-isospin excess parameters. The isothermal compressibility of polarized nuclear matter was also studied. The volume compressibility ${K}_{v}$ was found to decrease with temperature. The symmetry compressibility ${K}_{x},$ the spin symmetry compressibility ${K}_{y},$ and the spin-isospin symmetry compressibility ${K}_{z}$ were found to have a little increasing behavior with temperature.

Sideward flow in Au + Au collisions at 400 A.MeV

Abstract We present new experimental data obtained with the FOPI detector at SIS, for the Au + Au heavy-ion collisions at 400 A MeV incident energy. The sideward flow, determined from a method without reaction-plane reconstruction, and the nuclear stopping are studied as a function of the centrality of the collisions. In order to study the nuclear in-medium effects, which act on the NN cross sections and potential and hence on experimental observables like the nuclear-matter flow and stopping, these results are compared with the predictions of two different QMD versions. The first one offers a fully microscopic calculation of the cross sections and potential in the G-matrix formalism and naturally includes the in-medium effects (this version is for the first time confronted with experiment). The second one uses a standard Skyrme potential plus a momentum-dependent term in order to mimic the in-medium effects.

Nuclear dynamics for heavy ion collisions with a momentum dependent potential

Abstract The Boltzmann-Nordheim-Vlasov equation has been solved by using a microscopic momentum dependent (MD) nuclear mean field. This potential has been calculated in the framework of the self consistent Brueckner theory up to the second order in the G -matrix. Comparison with the so called soft and stiff Equation of State (EOS) is presented, using the Skyrme force. The calculations have been performed for 40 Ca+ 40 Ca and 93 Nb+ 93 Nb reactions, from the balance energy up to E lab =800 A MeV. At variance with the MD phenomenological potentials, the results at higher energy show that our soft EOS with MD mean field gives predictions which do not differ very much from the soft EOS with Skyrme potential without momentum dependence. On the other hand, at lower energy the MD potential has a behaviour which is quite different from both soft and stiff EOS, especially as far as the balance energy is concerned.

Quantum molecular dynamics and particle production in heavy ion collisions

The production of photons, kaons, antikaons and antiprotons in heavy-ion collisions is calculated in the framework of “quantum” molecular dynamics (QMD). The Skyrme potentials, with parameters chosen to generate the soft and hard nuclear equations of state(EOS), are used in the propagation of nucleons within QMD. The sensitivity of the production of each type of particle to the EOS is discussed. The mechanisms of production processes are studied. The theoretical results are compared with the available experimental data.

Subthreshold K+ production in 1GeV/u 197Au + 197Au collisions

We calculate the K +-production cross section in 197Au+ 197Au collisions at 1 GeV/u in the framework of quantum molecular dynamics (QMD). The Skyrme potentials, with parameters chosen to generate the soft and hard nuclear equations of state, are used in the propagation of nucleons within QMD. Our calculations show that the kaons are produced from an earlier stage of the collisions and mainly through a two-step process. Theoretical predictions with the soft equation of state are in good agreement with the experimental data from SIS at GSI. The results for soft and hard equations of state differ by approximately a factor 2 to 3.

In-medium effects in the description of heavy-ion collisions with realistic NN interactions

The simulations of 40Ca + 40Ca and 93Nb + 93Nb collisions at E lab = 400 MeV/u have been performed within the quantum molecular dynamics approach using both the phenomenological Skyrme forces and the Brueckner G-matrix potential as the in-medium NN interaction. The influence of the density and momentum dependence of the interaction on the time evolution of heavy-ion collisions is studied in detail. We found that the momentum dependence of the in-medium interaction strongly affects the density and temperature of the nuclear matter formed during collisions. Most of the results obtained for different observables are shown to be more sensitive to the momentum dependence of the interaction than to the nuclear equation of state. The strong repulsive G-matrix potential acting between nucleons with large relative momenta in the low-density region leads to an appreciably larger transverse momentum transfer and a smaller number of NN collisions compared with those obtained using the Skyrme potentials. Results obtained with the medium-dependent G-matrix NN cross section and those obtained with the phenomenological NN cross section parametrized by Cugnon et al. for the collision term are also compared.

Intermediate-energy heavy-ion collisions with G-matrix potentials and cross sections

We present the first quantum molecular dynamics calculations of heavy-ion collisions in which the effective nucleon-nucleon potential and the nucleon-nucleon cross sections in a medium are consistently calculated in the Brueckner theory from the basic Reid soft-core potential. The strong momentum dependence of the Brueckner G-matrix yields a quite different time evolution of heavy-ion collisions as compared with that obtained via Skyrme potentials adjusted to nuclear matter properties and the optical potential. In the calculation of Nb+Nb collisions at 400 MeV/u, we find that the transverse momentum transfer is much larger than that obtained with the hard Skyrme potential, although the compressibility ( K = 182MeV) is even lower than that of the soft Skyrme potential ( K = 200MeV). This raises questions about the possibility of uniquely determining the parameters of the nuclear equation of state from heavy-ion collisions at intermediate energies. The momentum transfer has two physically quite different reasons: the strong momentum dependence of the G-matrix potential causes a strong transverse momentum very early in the time evolution of the reaction, i.e. before the system is compressed. Additional transverse momentum is transferred in the compression phase, similar to observations for Skyrme-like potentials. The momentum transfer in the second process is about that of the soft Skyrme potential, which is not unexpected because the compressibilities are similar and in both calculations about the same density is reached.

The Skyrme Potential and Elastic Nucleon Scattering from 12C

It is investigated whether the Skyrme potential is applicable for the microscopic coupled channels analysis of nucleon-12C scattering in the resonance energy region. After studying carefully the conformity between our microscopic treatment and the phenomenological model, we carried out the numerical analysis of the nucleon-12C system, replacing the phenomenological coupling potential form factor by the microscopic one in the phenomenological coupled channels equations. Satisfactory agreements were obtained between theory and experiment. It is concluded that the microscopic coupling potential form factor constructed from the Skyrme potential yields correct effects of the coupling between the target ground and excited states.

Fusion calculations with the Skyrme interactions

The effect on nuclear dynamics of using various parametrizations of the Skyrme potential is studied. In particular, fusion cross sections for the light system $^{16}\mathrm{O}$ + $^{24}\mathrm{Mg}$ are calculated for the interactions Skyrme II, Skyrme III, Skyrme IV, Skyrme V, and Skyrme VI. The interaction Skyrme III is shown to increase significantly the fusion cross section. An angular momentum window for fusion is observed to occur for ${E}_{\mathrm{c}.\mathrm{m}.}\ensuremath{\gtrsim}70$ MeV.NUCLEAR REACTIONS $^{16}\mathrm{O}$($^{24}\mathrm{Mg}$,$x$) in time-dependent Hartree-Fock approximation. Effect of nuclear interaction on fusion cross section.

Time-dependent Hartree-Fock calculations of fusion cross sections for the reactionsO16+O16andCa40+Ca40

We have calculated total fusion cross sections for the reactions /sup 16/O + /sup 16/O and /sup 40/Ca + /sup 40/Ca using time-dependent Hartree-Fock theory in the rotating frame approximation. The full Skyrme potential has been employed, and neutrons and protons have been treated separately in the calculations. The results show that the fusion cross sections for the /sup 40/Ca + /sup 40/Ca system at low bombarding energy are greatly enhanced by the elimination of the previously enforced neutron-proton symmetry. Approximate inclusion of the Coulomb exchange term does not affect the results in either of the light systems studied. The results are in semiquantitative agreement with experiment, and the sensitivity of the calculations to the effective interaction employed suggests that the discrepancy between theoretical and experimental results can be substantially reduced.