Quartetting Wave Function Approach to 20^{20}Ne: Shell Model and Local Density Approximation

We investigate $\alpha$-like correlations in $^{20}$Ne. A quartet of nucleons (different spin/isospin) is moving in a mean field produced by the $^{16}$O core nucleus. Improving the Thomas-Fermi model (local density approach), a shell model is considered for the core nucleus. The effective potential of the $\alpha$-like quartet and the wave function for the center-of-mass (c.o.m.) motion are calculated and compared with other approaches.Comment: 10 pages, 7 figures. arXiv admin note: substantial text overlap with arXiv:1707.0451

Correlations and Clustering in Dilute Matter

Nuclear systems are treated within a quantum statistical approach. Correlations and cluster formation are relevant for the properties of warm dense matter, but the description is challenging and different approximations are discussed. The equation of state, the composition, Bose condensation of bound fermions, the disappearance of bound states at increasing density because of Pauli blocking are of relevance for different applications in astrophysics, heavy ion collisions, and nuclear structure.Comment: 22 pages, 7 figures, contribution to the special-topics volume on nuclear correlations and cluster physics, edited by W. U. Schr\"ode

Following multi-dimensional Type Ia supernova explosion models to homologous expansion

The last years have witnessed a rapid development of three-dimensional models of Type Ia supernova explosions. Consequently, the next step is to evaluate these models under variation of the initial parameters and to compare them with observations. To calculate synthetic lightcurves and spectra from numerical models, it is mandatory to follow the evolution up to homologous expansion. We report on methods to achieve this in our current implementation of multi-dimensional Type Ia supernova explosion models. The novel scheme is thoroughly tested in two dimensions and a simple example of a three-dimensional simulation is presented. We discuss to what degree the assumption of homologous expansion is justified in these models.Comment: 15 pages, 16 figures, resolution of some figures reduced to meet astro-ph file size restriction, submitted to A&

Double-detonation supernovae of sub-Chandrasekhar mass white dwarfs

In the "double-detonation sub-Chandrasekhar" model for type Ia supernovae, a carbon-oxygen (C + O) white dwarf accumulates sufficient amounts of helium such that a detonation ignites in that layer before the Chandrasekhar mass is reached. This detonation is thought to trigger a secondary detonation in the C + O core. By means of one- and two-dimensional hydrodynamic simulations, we investigate the robustness of this explosion mechanism for generic 1-M_sun models and analyze its observable predictions. Also a resolution dependence in numerical simulations is analyzed. The propagation of thermonuclear detonation fronts, both in helium and in the carbon-oxygen mixture, is computed by means of both a level-set function and a simplified description for nuclear reactions. The decision whether a secondary detonation is triggered in the white dwarf's core or not is made based on criteria given in the literature. In a parameter study involving different initial flame geometries for He-shell masses of 0.2 and 0.1 M_sun, we find that a secondary detonation ignition is a very robust process. Converging shock waves originating from the detonation in the He shell generate the conditions for a detonation near the center of the white dwarf in most of the cases considered. Finally, we follow the complete evolution of three selected models with 0.2 M_sun of He through the C/O-detonation phase and obtain nickel-masses of about 0.40 to 0.45 M_sun. Although we have not done a complete scan of the possible parameter space, our results show that sub-Chandrasekhar models are not good candidates for normal or sub-luminous type Ia supernovae. The chemical composition of the ejecta features significant amounts of nickel in the outer layers at high expansion velocities, which is inconsistent with near-maximum spectra. (abbreviated)Comment: 11 pages, 10 figures, PDFLaTeX, accepted for publication in A&

Light clusters in nuclear matter: Excluded volume versus quantum many-body approaches

The formation of clusters in nuclear matter is investigated, which occurs e.g. in low energy heavy ion collisions or core-collapse supernovae. In astrophysical applications, the excluded volume concept is commonly used for the description of light clusters. Here we compare a phenomenological excluded volume approach to two quantum many-body models, the quantum statistical model and the generalized relativistic mean field model. All three models contain bound states of nuclei with mass number A <= 4. It is explored to which extent the complex medium effects can be mimicked by the simpler excluded volume model, regarding the chemical composition and thermodynamic variables. Furthermore, the role of heavy nuclei and excited states is investigated by use of the excluded volume model. At temperatures of a few MeV the excluded volume model gives a poor description of the medium effects on the light clusters, but there the composition is actually dominated by heavy nuclei. At larger temperatures there is a rather good agreement, whereas some smaller differences and model dependencies remain.Comment: 12 pages, 6 figures, published version, minor change

Deuteron formation in nuclear matter

We investigate deuteron formation in nuclear matter at finite temperatures within a systematic quantum statistical approach. We consider formation through three-body collisions relevant already at rather moderate densities because of the strong correlations. The three-body in-medium reaction rates driven by the break-up cross section are calculated using exact three-body equations (Alt-Grassberger-Sandhas type) that have been suitably modified to consistently include the energy shift and the Pauli blocking. Important quantities are the lifetime of deuteron fluctuations and the chemical relaxation time. We find that the respective times differ substantially while using in-medium or isolated cross sections. We expect implications for the description of heavy ion collisions in particular for the formation of light charged particles at low to intermediate energies.Comment: 19 pages, 5 figure