The quark-meson coupling model for Λ, Σ and Ξ hypernuclei

The quark-meson coupling (QMC) model, which has been successfully used to describe the properties of both infinite nuclear matter and finite nuclei, is applied to a systematic study of Λ, Σ and Ξ hypernuclei. Assumptions made in the present study are, (i) the (self-consistent) exchanged scalar, and vector, mesons couple only to the u and d quarks, and (ii) an SU(6) valence quark model for the bound nucleons and hyperon. The model automatically leads to a very weak spin-orbit interaction for the Λ in a hypernucleus. Effects of the Pauli blocking at the quark level, particularly in the open, coupled, ΣN-ΛN chanel (strong conversion), is also taken into account in a phenomenological way.     

Three-dimensional structure of low-density nuclear matter

We numerically explore the pasta structures and properties of low-density nuclear matter without any assumption on the geometry. We observe conventional pasta structures, while a mixture of the pasta structures appears as a metastable state at some transient densities. We also discuss the lattice structure of droplets.     

Strangeness production in proton—proton and proton—nucleus collisions

We discuss the investigation of the strange meson production in proton-proton (pp) and proton-nucleus (pA) reactions within an effective Lagrangian model. The kaon production proceeds mainly via excitations ofN*(1650),N*(1710), andN* (1720) resonant intermediate nucleonic states, in the collision of two initial state nucleons. Therefore, the strangeness production is expected to provide information about the resonances lying at higher excitation energies. For beam energies very close to the kaon production threshold the hyperon-proton final state interaction effects are quite important. Thus, these studies provide a check on the models of hyperon-nucleon interactions. The inmedium production of kaons shows strong sensitivity to the self-energies of the intermediate mesons     

Low mass dilepton production at ultrarelativistic energies

Dilepton production in pp and Au+Au nucleus–nucleus collisions at as well as in In+In and Pb+Au at is studied within the microscopic HSD transport approach. A comparison to the data from the PHENIX Collaboration at RHIC shows that standard in-medium effects of the ρ,ω vector mesons—compatible with the NA60 data for In+In at and the CERES data for Pb+Au at —do not explain the large enhancement observed in the invariant mass regime from 0.2 to 0.5 GeV in Au+Au collisions at relative to pp collisions.     

Geometrical order-of-magnitude estimates for spatial curvature in realistic models of the Universe

The thoughts expressed in this article are based on remarks made by Jürgen Ehlers at the Albert-Einstein-Institut, Golm, Germany in July 2007. The main objective of this article is to demonstrate, in terms of plausible order-of-magnitude estimates for geometrical scalars, the relevance of spatial curvature in realistic models of the Universe that describe the dynamics of structure formation since the epoch of matter–radiation decoupling. We introduce these estimates with a commentary on the use of a quasi-Newtonian metric form in this context. In memoriam: Jürgen Ehlers (1929–2008).     

Nuclear magnetic moment: Relativistic mean field description

Valence nucleon effective mass, which is almost constant, is proposed within the relativistic mean field theories of finite nuclei (closed shell ± one nucleon). It acquires a slight spin-orbit splitting due to relativistic effects. The relativistic Dirac magnetic moment is rewritten analytically in terms of angular momentum-Pauli spin coupled states and the effective mass. Introducing the nucleon effective charge, the iso-scalar and iso-vector corrections to the magnetic moment operator are extracted from the overall one parameter fit of the measured and the calculated values. The calculated values of magnetic moments are in overall fair agreement with the experiment as well as with the other detailed microscopic calculations.     

Structure of light hypernuclei

The structure of light hypernuclei with strangeness S=−1 and −2 is investigated with the microscopic cluster model and the Gaussian expansion method (GEM). We emphasize that the cluster picture as well as the mean-field picture is invaluable to understand the structure of Λ hypernuclei, Σ hypernuclei and double Λ hypernuclei. A variety of aspects of Λ hypernuclei is demonstrated through a systematic study of p-shell hypernuclei (,, , , , , ) and sd-shell ones (, ): for example, the appearance of genuine hypernuclear states with new spatial symmetry which cannot be seen in ordinary nuclei, the glue-like role of the Λ particle which shrinks the size of nuclear core and thus reduces the B(E2) value, and the halo and skin structures in and etc. The typical light hypernucleus is thoroughly investigated, including its production, structure and decay. Precise three-body and four-body calculations of , and using GEM provide important information on the spin structure of the underlying ΛN interaction, by comparing with recent experimental data from γ-ray hypernuclear spectroscopy. The Λ–Σ coupling effect is studied in and . The binding mechanism of is discussed together with the possible existence of , emphasizing the fact that the study of is useful for extracting information on the ΣN interaction differing from that from . A systematic study of double-Λ hypernuclei, constrained by the NAGARA data () within a four-body cluster model indicates that the recently observed Demachi–Yanagi event can be interpreted as the 2⁺ state of . The effect of hyperon mixing in and is investigated using one-boson-exchange potentials and quark-cluster-model interactions for the S=−2 sector. A close relation between nuclear deep hole states and hypernuclei is discussed, emphasizing the selection rule for fragmentation of the s-hole in light nuclei, which is promising for understanding the production mechanism of double-Λ and twin-Λ hypernuclei via Ξ-atomic capture.     

Production of light nuclei,hypernuclei and their antiparticles in relativistic nuclear collisions

We present, using the statistical model, an analysis of the production of light nuclei, hypernuclei and their antiparticles in central collisions of heavy nuclei. Based on these studies we provide predictions for the production yields of multiply-strange light nuclei.     

Nonlinear diffusion and particle production in relativistic systems

The short parton production phase in high-energy heavy-ion collisions is treated analytically as a nonlinear diffusion process. The initial buildup of the rapidity density distributions of produced charged hadrons within τ_p0.25 fm/c occurs in three sources during the colored partonic phase. In a two-step approach, the subsequent diffusion in pseudorapidity space during the interaction time of τ_int7–10 fm/c (mean duration of the collision) is essentially linear as expressed in the Relativistic Diffusion Model (RDM) which yields excellent agreement with the data at RHIC energies, and allows for predictions at LHC energies. Results for d+Au are discussed in detail.     

A relativistic mean-field study of magic numbers in light nuclei from neutron to proton drip-lines

In an axially deformed relativistic mean-field calculation of single-particle energy spectra ofN = 8 (Li-Mg) andN = 14,16 (C-Mg) isotonic chain and the one- and two-neutron separation energies of various isotopes of Li-Mg, new magic numbers are found to exist atN = 6 andN = 16 and/orN = 14, which are in addition to theN = 8 andN = 20 magic numbers. In neutron-rich nuclei, the shell gap atN = 6 is larger than atN = 8 and a large gap is observed forN = 16 or 14 for the neutron-rich andN = 14 for proton-rich nuclei. Large shell gaps are also found to exist atN = 14 and 16 orN = 16 alone for nuclei near theβ-stability line. The above results are independent of the parameter sets TM2, NL3 and NL-SH used here. Similarly, new large shell gaps are predicted atZ = 616 and/or 14 for protons.     

Strange hadron production in heavy ion collisions from SPS to RHIC

Strange particles have been a very important observable in the search for a deconfined state of strongly interacting matter, the quark–gluon plasma (QGP), which is expected to be formed in ultra-relativistic heavy ion collisions. We review the main experimental observations made at the Super Proton Synchrotron (SPS) at CERN, Geneva, and at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL). The large amount of recently collected data allows for a comprehensive study of strangeness production as a function of energy and system size. We review results on yields, transverse mass and rapidity spectra, as well as elliptic flow. The measurements are interpreted in the context of various theoretical concepts and their implications are discussed. Of particular interest is the question whether strange particles are in any way sensitive to a partonic phase. Finally, a compilation of experimental data is provided.     

On the mean field theory bound on the magnetization

The mean field bound on magnetization is proved for a class of one-component ferromagnetic systems and forD components systems with arbitraryD.     

Exotic nuclei – a challenge for nuclear mean field models

We present a brief overview of the interplay between exotic nuclei and the development of nuclear mean field models. This is exemplified with four test cases addressing the topics of shape coexistence, isotope shifts, long isotopic chains, and superheavy elements. This revised version was published online in August 2006 with corrections to the Cover Date.     

Hadron production and phase changes in relativistic heavy-ion collisions

We study soft hadron production in relativistic heavy-ion collisions in a wide range of reaction energy, 4.8 GeV < < 200 GeV, and make predictions about yields of particles using the statistical hadronization model. In fits to experimental data, we obtain both the statistical parameters as well as physical properties of the hadron source. We identify the properties of the fireball at the critical energy threshold, 6.26 GeV < < 7.61 GeV, marking for higher energies the hadronization of an entropy-rich phase. In terms of the chemical composition, one sees a phase which at low energy is chemically under-saturated, and which turns into a chemically over-saturated state persisting up to the maximum accessible energy. Assuming that there is no change in physical mechanisms in the energy range 15 > ≥200 GeV, we use continuity of particle yields and statistical parameters to predict the hadron production at = 62.4 GeV, and obtain total yields of hadrons at = 130 GeV. We consider, in depth, the pattern we uncover within the hadronization condition, and discuss possible mechanisms associated with the identified rapid change in system properties at . We propose that the chemically over-saturated 2 + 1 flavor hadron matter system undergoes a 1st-order phase transition.     

Recent physics at COSY — a review

The COSY accelerator in Jülich is presented together with its internal and external detectors. The physics program performed recently is discussed with emphasis on strangeness physics and precision experiments     

Nonextensive nuclear liquid–gas phase transition

We study an effective relativistic mean-field model of nuclear matter with arbitrary proton fraction at finite temperature in the framework of nonextensive statistical mechanics, characterized by power-law quantum distributions. We investigate the presence of thermodynamic instability in a warm and asymmetric nuclear medium and study the consequent nuclear liquid–gas phase transition by requiring the Gibbs conditions on the global conservation of baryon number and electric charge fraction. We show that nonextensive statistical effects play a crucial role in the equation of state and in the formation of mixed phase also for small deviations from the standard Boltzmann–Gibbs statistics.     

Neutron halos in hypernuclei

Properties of single- Λ and double- Λ hypernuclei for even-N Ca isotopes ranging from the proton dripline to the neutron dripline are studied using the relativistic continuum Hartree-Bogoliubov theory with a zero-range pairing interaction. Compared with ordinary nuclei, the addition of one or two Λ-hyperons lowers the Fermi level. The predicted neutron dripline nuclei are, respectively, ⁷⁵ _ΛCa and ⁷⁶ _2ΛCa, as the additional attractive force provided by the Λ-N interaction shifts nuclei from outside to inside the dripline. Therefore, the last bound hypernuclei have two more neutrons than the corresponding ordinary nuclei. Based on the analysis of two-neutron separation energies, neutron single-particle energy levels, the contribution of continuum and nucleon density distribution, giant halo phenomena due to the pairing correlation, and the contribution from the continuum are suggested to exist in Ca hypernuclei similar to those that appear in ordinary Ca isotopes. Received: 21 October 2002 / Accepted: 11 January 2003 / Published online: 8 April 2003