Direct Reactions with Exotic Nuclei, Nuclear Structure and Astrophysics

Intermediate energy Coulomb excitation and dissociation is a useful tool for nuclear structure and astrophysics studies. Low-lying strength in nuclei far from stability was discovered by this method. The effective range theory for low-lying strength in one-neutron halo nuclei is summarized and extended to two-neutron halo nuclei. This is of special interest in view of recent rather accurate experimental results on the low-lying electric dipole strength in $^{11}$Li. Another indirect approach to nuclear astrophysics is the Trojan horse method. It is pointed out that it is a suitable tool to investigate subthreshold resonances.Comment: 8 pages, 2 figures, Proceedings of the Erice School on 'Radioactive Beams, Nuclear Dynamics and Astrophysics' to be published in 'Prog. Part. Nucl. Phys.

Direct Reactions with Exotic Nuclei

We discuss recent work on Coulomb dissociation and an effective-range theory of low-lying electromagnetic strength of halo nuclei. We propose to study Coulomb dissociation of a halo nucleus bound by a zero-range potential as a homework problem. We study the transition from stripping to bound and unbound states and point out in this context that the Trojan-Horse method is a suitable tool to investigate subthreshold resonances.Comment: 9 pages, 1 figure, proceedings of Workshop on "Reaction Mechanisms for Rare Isotope Beams" Michigan State University March 9-12,200

Investigation of subthreshold resonances with the Trojan horse method

It is pointed out that the Trojan horse method is a suitable tool to investigate subthreshold resonances.Comment: references added, typo corrected;6 pages, 1 figure, to be published in the AIP Proceedings of Fusion06, International Conference on Reaction Mechanisms and Nuclear Structure at the Coulomb Barrier, March 19-23, 2006, San Servolo, Ital

E0 emission in alpha + ^12C fusion at astrophysical energies

We show that E0 emission in alpha + ^12C fusion at astrophysically interesting energies is negligible compared to E1 and E2 emission.Comment: submitted to Phys. Rev. C, Brief Report

Strangeness in the cores of neutron stars

The measurement of the mass 1.97 +/- 0.04 M_sun for PSR J1614-2230 provides a new constraint on the equation of state and composition of matter at high densities. In this contribution we investigate the possibility that the dense cores of neutron stars could contain strange quarks either in a confined state (hyperonic matter) or in a deconfined one (strange quark matter) while fulfilling a set of constraints including the new maximum mass constraint. We account for the possible appearance of hyperons within an extended version of the density-dependent relativistic mean-field model, including the phi-meson interaction channel. Deconfined quark matter is described by the color superconducting three-flavor NJL model.Comment: 6 pages, 2 figures, contribution to "Strangeness in Quark Matter 2011", Cracow, September 18-24, 201

Relativistic model for nuclear matter and atomic nuclei with momentum-dependent self-energies

The Lagrangian density of standard relativistic mean-field (RMF) models with density-dependent meson-nucleon coupling vertices is modified by introducing couplings of the meson fields to derivative nucleon densities. As a consequence, the nucleon self energies, that describe the effective in-medium interaction, become momentum dependent. In this approach it is possible to increase the effective (Landau) mass of the nucleons, that is related to the density of states at the Fermi energy, as compared to conventional relativistic models. At the same time the relativistic effective (Dirac) mass is kept small in order to obtain a realistic strength of the spin-orbit interaction. Additionally, the empirical Schroedinger-equivalent central optical potential from Dirac phenomenology is reasonably well described. A parametrization of the model is obtained by a fit to properties of doubly magic atomic nuclei. Results for symmetric nuclear matter, neutron matter and finite nuclei are discussed.Comment: 14 pages, 7 figures, 5 tables, extended introduction and conclusions, additional references, minor corrections, accepted for publication in Phys. Rev.

Effects of the liquid-gas phase transition and cluster formation on the symmetry energy

Various definitions of the symmetry energy are introduced for nuclei, dilute nuclear matter below saturation density and stellar matter, which is found in compact stars or core-collapse supernovae. The resulting differences are exemplified by calculations in a theoretical approach based on a generalized relativistic density functional for dense matter. It contains nucleonic clusters as explicit degrees of freedom with medium dependent properties that are derived for light clusters from a quantum statistical approach. With such a model the dissolution of clusters at high densities can be described. The effects of the liquid-gas phase transition in nuclear matter and of cluster formation in stellar matter on the density dependence of the symmetry energy are studied for different temperatures. It is observed that correlations and the formation of inhomogeneous matter at low densities and temperatures causes an increase of the symmetry energy as compared to calculations assuming a uniform uncorrelated spatial distribution of constituent baryons and leptons.Comment: 20 pages, 19 figures, version accepted for publication in EPJA special volume on Nuclear Symmetry Energ

Higher order effects in electromagnetic dissociation of neutron halo nuclei

We investigate higher order effects in electromagnetic dissociation of neutron halo nuclei using a simple and realistic zero range model for the neutron-core interaction. In the sudden (or Glauber) approximation all orders in the target-core interaction are taken into account. Small deviations from the sudden approximation are readily calculated. We obtain very simple analytical results for the next-to-leading order effects, which have a simple physical interpretation. For intermediate energy electromagnetic dissociation, higher order effects are generally small. We apply our model to Coulomb dissociation of $^{19}$C at 67 A MeV. The analytical results are compared to numerical results from the integration of the time-dependent Schroedinger equation. Good agreement is obtained. We conclude that higher order electromagnetic effects are well under control

Accessibility of color superconducting quark matter phases in heavy-ion collisions

We discuss a hybrid equation of state (EoS) that fulfills constraints for mass-radius relationships and cooling of compact stars. The quark matter EoS is obtained from a Polyakov-loop Nambu--Jona-Lasinio (PNJL) model with color superconductivity, and the hadronic one from a relativistic mean-field (RMF) model with density-dependent couplings (DD-RMF). For the construction of the phase transition regions we employ here for simplicity a Maxwell construction. We present the phase diagram for symmetric matter which exhibits two remarkable features: (1) a "nose"-like structure of the hadronic-to-quark matter phase border with an increase of the critical density at temperatures below T ~ 150 MeV and (2) a high critical temperature for the border of the two-flavor color superconducting (2SC) phase, T_c > 160 MeV. We show the trajectories of heavy-ion collisions in the plane of excitation energy vs. baryon density calculated using the UrQMD code and conjecture that for incident energies of 4 ... 8 A GeV as provided, e.g., by the Nuclotron-M at JINR Dubna or by lowest energies at the future heavy-ion collision experiments CBM@FAIR and NICA@JINR, the color superconducting quark matter phase becomes accessible.Comment: 5 pages, 1 figure, Poster presented at the XXVI. Max Born Symposium "Three Days of Strong Interactions", Wroclaw (Poland), July 9-11, 200