Publications (26)87.76 Total impact
 [Show abstract] [Hide abstract] ABSTRACT: The Microscopic Otical Model Potential is evaluated within a relativistic scheme which provides a natural and consistent relation between the spinorbit part and the central part of the potential. The DiracBruecknerHartreeFock (DBHF) approach provides such a microscopic relativistic scheme, which is based on a realistic nucleonnucleon interaction and reproduce the saturation properties of symmetric nuclear matter without any adjustable parameter. Its solution using the projection technique within the subtracted Tmatrix (STM) representation provides a reliable extension to asymmetric nuclear matter, which is important to describe the features of the isospin asymmetric nuclei. Therefore, the present work aims to perform a global analysis of the isospindependent nucleonnucleus MOP based on the DBHF calculation in symmetric and asymmetric nuclear matter. The DBHF is used to evaluate the relativistic structure of the nucleon selfenergies in nuclear matter at various densities and asymmetries. The Schr\"odinger equivalent potentials of finite nuclei are derived from these Dirac components by a local density approximation (LDA). The nucleonnucleus scattering calculations are carried out for a broad spectrum $n$ and $p$ scattering experiments below 200 MeV with targets ranging from $^{12}$C to $^{208}$Pb.
 [Show abstract] [Hide abstract] ABSTRACT: We present a simultaneous calculation of heavy single$\Lambda$ hypernuclei and compact stars containing hypernuclear core within a relativistic density functional theory based on a Lagrangian which includes the hyperon octet and lightest isoscalarisovector mesons which couple to baryons with densitydependent couplings. The corresponding density functional allows for SU(6) symmetry breaking and mixing in the isoscalar sector, whereby the departures in the $\sigma$$\Lambda$ and $\sigma$$\Sigma$ couplings away from their values implied by the SU(3) symmetric model are used to adjust the theory to the laboratory and astronomical data. We fix $\sigma$$\Lambda$ coupling using the data on the single$\Lambda$ hypernuclei and derive an upper bound on the $\sigma$$\Sigma$ from the requirement that the lower bound on the maximum mass of a compact star is $2 M_{\odot}$.
 [Show abstract] [Hide abstract] ABSTRACT: The structure of finite nuclei is investigated by employing an interaction model which is based on the lowmomentum interaction $V_{lowk}$. It is supplemented by a densitydependent contact interaction fitted to reproduce the saturation properties of infinite nuclear matter within the HartreeFock approach. The calculations of finite nuclei are performed in a basis of plane waves discretized in a cartesian box of appropriate size. As a first example the structure of Ne isotopes is considered ranging from $^{18}$Ne to the neutron drip line. Rather good agreement is obtained for the bulk properties of these nuclei without any free parameter. The basis is also appropriate to describe other deformed nuclei and the transition from discrete nuclei to homogeneous matter which is supposed to occur in the crust of neutron stars.
 [Show abstract] [Hide abstract] ABSTRACT: A density dependent relativistic meanfield model is determined to reproduce the components of the nucleon selfenergy at low densities. This model is used to investigate spinodal instabilities in isospin asymmetric nuclear matter at finite temperatures. The inhomogeneous density distributions in the spinodal region are investigated through calculations in a cubic WignerSeitz cell. Compared to results obtained in phenomenological calculations the spinodal region is large, i.e. the spinodal region at zero temperature can reach densities above 0.12 fm$^{3}$. The predicted spinodal region is concentrated around isospin symmetric nuclear matter and the critical temperature is considerably lower than in the previous microscopic based investigation within a nonrelativistic BruecknerHartreeFock approach.
 [Show abstract] [Hide abstract] ABSTRACT: The relativistic optical model potential (OMP) for nucleonnucleus scattering is investigated in the framework of DiracBruecknerHartreeFock (DBHF) approach using the BonnB OneBoson Exchange potential for the bare nucleonnucleon interaction. Both real and imaginary parts of isospindependent nucleon selfenergies in nuclear medium are derived from the DBHF approach based on the projection techniques within the subtracted T matrix representation. The Dirac potentials as well as the corresponding Schrodinger equivalent potentials are evaluated. An improved local density approximation is employed in this analysis, where a range parameter is included to account for a finiterange correction of the nucleonnucleon interaction. As an example the total cross sections, differential elastic scattering cross sections, analyzing powers for n, p + 27Al at incident energy 100 keV < E < 250 MeV are calculated. The results derived from this microscopic approach of the OMP are compared to the experimental data, as well as the results obtained with a phenomenological OMP. A good agreement between the theoretical results and the measurements can be achieved for all incident energies using a constant value for the range parameter.
 [Show abstract] [Hide abstract] ABSTRACT: A set of relativistic mean field models is constructed including the Hartree and HartreeFock approximation accounting for the exchange of isoscalar and isovector mesons as well as the pion. Density dependent coupling functions are determined to reproduce the components of the nucleon selfenergy at the Fermi surface, obtained within the DiracBruecknerHartreeFock (DBHF) approach using a realistic nucleonnucleon interaction. It is investigated, to which extend the various mean field models can reproduce the DBHF results for the momentum dependence of the selfenergies and the total energy of infinite matter. The mean field models are also used to evaluate the bulk properties of spherical closedshell nuclei. We find that the HartreeFock model allowing for the exchange of $\sigma,\,\omega,\,\rho,\,\delta$ mesons and pions, yield the best reproduction of the DBHF results in infinite matter and also provides a good description of the properties of finite nuclei without any adjustment of parameters.
 [Show abstract] [Hide abstract] ABSTRACT: The offshell behavior of the nucleon selfenergy in isospinasymmetric nuclear matter is investigated within the framework of the relativistic DiracBruecknerHartreeFock approach based on projection techniques. The dependence of the Dirac components of the selfenergy on momentum as well as energy is evaluated for symmetric as well as asymmetric nuclear matter. Special attention is paid to the various contributions to the momentum dependence of the real and imaginary part of the optical potential. The consequences to the different definitions of the effective nucleon mass and particle spectral functions are discussed.
 [Show abstract] [Hide abstract] ABSTRACT: The status of relativistic nuclear manybody calculations of nuclear systems to be built up in terms of protons and neutrons is reviewed. In detail, relativistic effects on several aspects of nuclear matter such as the effective mass, saturation mechanism, and the symmetry energy are considered. This review will especially focus on isospin asymmetric issues, since these aspects are of high interest in astrophysical and nuclear structure studies. Furthermore, from the experimental side these aspects are experiencing an additional boost from a new generation of radioactive beam facilities, e.g. the future GSI facility FAIR in Germany or SPIRAL2 at GANIL/France. Finally, the prospects of studying finite nuclei in microscopic calculations which are based on realistic $NN$ interactions by including relativistic effects in calculations of low momentum interactions are discussed.
 [Show abstract] [Hide abstract] ABSTRACT: The lowmomentum interaction $V_{\text{lowk}}$ derived from realistic models of the nucleonnucleon interaction is presented in a separable form. This separable force is supported by a contact interaction in order to achieve the saturation properties of symmetric nuclear matter. Bulk properties of nuclear matter and finite nuclei are investigated for the separable form of $V_{\text{lowk}}$ and two different parameterizations of the contact term. The accuracy of the separable force in HartreeFock calculations with respect to the original interaction $V_{\text{lowk}}$ is discussed. For a cutoff parameter $\Lambda$ of 2 fm$^{1}$ a representation by a rank 2 separable force yields a sufficient accuracy, while higher ranks are required for larger cutoff parameters. The resulting separable force is parameterized in a simple way to allow for an easy application in other nuclear structure calculations. Comment: 11 pages, 7 figures
 [Show abstract] [Hide abstract] ABSTRACT: Closed shellnuclei are described employing an interaction model which is based on the lowmomentum interaction Vlowk. This effective twobody interaction which is determined to reproduce the nucleonnucleon (NN) scattering data at energies below the pion threshold is supplemented by a densitydependent contact interaction fitted to reproduce the saturation properties of infinite nuclear matter within the HartreeFock approach. It is demonstrated that corresponding calculations for closed shell nuclei using this interaction model reproduce the bulk properties of these nuclei in a basis of plane waves discretized in a spherical box of appropriate size. This plane wave basis is very appropriate to describe weakly bound nuclei close to the neutron drip line and the transition from discrete nuclei to homogeneous matter which is supposed to occur, e.g., in the crust of neutron stars.
 [Show abstract] [Hide abstract] ABSTRACT: Relativistic effects are investigated in nuclear matter calculations employing renormalized lowmomentum nucleonnucleon ($NN$) interactions. It is demonstrated that the relativistic effects cure a problem of nonrelativistic lowmomentum interactions, which fail to reproduce saturation of nuclear matter. Including relativistic effects, one already obtains saturation in a HartreeFock calculation. BruecknerHartreeFock calculations lead to a further improvement of the saturation properties. The results are rather insensitive to the realistic $NN$ interaction on which they are based. Comment: 4 pages, 3 figures

Article: Properties of asymmetric nuclear matter in different approaches, Physical Review C79, 024308 (2009).
[Show abstract] [Hide abstract] ABSTRACT: Properties of asymmetric nuclear matter are derived from various manybody approaches. This includes phenomenological ones like the Skyrme HartreeFock and relativistic mean field approaches, which are adjusted to fit properties of nuclei, as well as more microscopic attempts like the BruecknerHartreeFock approximation, a selfconsistent Greens function method and the socalled Vlowk approach, which are based on realistic nucleon nucleon interactions which reproduce the nucleonnucleon phase shifts. These microscopic approaches are supplemented by a densitydependent contact interaction to achieve the empirical saturation property of symmetric nuclear matter. The predictions of all these approaches are discussed for nuclear matter at high densities in βequilibrium. Special attention is paid to behavior of the isovector component of the effective mass in neutron rich matter.  [Show abstract] [Hide abstract] ABSTRACT: Properties of asymmetric nuclear matter are derived from various manybody approaches. This includes phenomenological ones like the Skyrme HartreeFock and relativistic mean field approaches, which are adjusted to fit properties of nuclei, as well as more microscopic attempts like the BruecknerHartreeFock approximation, a selfconsistent Greens function method and the socalled $V_{lowk}$ approach, which are based on realistic nucleonnucleon interactions which reproduce the nucleonnucleon phase shifts. These microscopic approaches are supplemented by a densitydependent contact interaction to achieve the empirical saturation property of symmetric nuclear matter. The predictions of all these approaches are discussed for nuclear matter at high densities in $\beta$equilibrium. Special attention is paid to behavior of the isovector component of the effective mass in neutronrich matter.

Article: Isospin Dependence of Nuclear Matter
[Show abstract] [Hide abstract] ABSTRACT: Exploring the isospin dependence of the nuclear matter is one of the main challenges of modern nuclear physics. The ab initio calculations are the proper tool for these investigations. Results of the DiracBruecknerHartreeFock calculations for asymmetric nuclear matter, which are based on improved approximation schemes, are presented. Furthermore, the application to finite nuclei is discussed.  [Show abstract] [Hide abstract] ABSTRACT: Properties of inhomogeneous nuclear matter are evaluated within a relativistic mean field approximation using density dependent coupling constants. A parameterization for these coupling constants is presented, which reproduces the properties of the nucleon selfenergy obtained in Dirac Brueckner Hartree Fock calculations of asymmetric nuclear matter but also provides a good description for bulk properties of finite nuclei. The inhomogeneous infinite matter is described in terms of cubic WignerSeitz cells, which allows for a microscopic description of the structures in the socalled ``pastaphase'' of nuclear configurations and provides a smooth transition to the limit of homogeneous matter. The effects of pairing properties and finite temperature are considered. A comparison is made to corresponding results employing the phenomenological Skyrme HartreeFock approach and the consequences for the ThomasFermi approximation are discussed.
 [Show abstract] [Hide abstract] ABSTRACT: We present DiracBruecknerHartreeFock calculations for isospin asymmetric nuclear matter which are based on improved approximations schemes. The potential matrix elements have been adapted for isospin asymmetric nuclear matter in order to account for the protonneutron mass splitting in a more consistent way. The proton properties are particularly sensitive to this adaption and its consequences, whereas the neutron properties remains almost unaffected in neutron rich matter. Although at present full Brueckner calculations are still too complex to apply to finite nuclei, these relativistic Brueckner results can be used as a guidance to construct a density dependent relativistic mean field theory, which can be applied to finite nuclei. It is found that an accurate reproduction of the DiracBruecknerHartreeFock equation of state requires a renormalization of these coupling functions. Comment: 34 pages, 9 figures, submitted to Eur. Phys. J. A
 [Show abstract] [Hide abstract] ABSTRACT: A new scheme for testing nuclear matter equations of state (EoSs) at high densities using constraints from neutron star (NS) phenomenology and a flow data analysis of heavyion collisions is suggested. An acceptable EoS shall not allow the direct Urca process to occur in NSs with masses below 1.5M⊙, and also shall not contradict flow and kaon production data of heavyion collisions. Compact star constraints include the mass measurements of 2.1±0.2M⊙ (1σ level) for PSR J0751+1807 and of 2.0±0.1M⊙ from the innermost stable circular orbit for 4U 1636–536, the baryon mass—gravitational mass relationships from Pulsar B in J0737–3039 and the massradius relationships from quasiperiodic brightness oscillations in 4U 0614+09 and from the thermal emission of RX J1856–3754. This scheme is applied to a set of relativistic EoSs which are constrained otherwise from nuclear matter saturation properties. We demonstrate on the given examples that the test scheme due to the quality of the newly emerging astrophysical data leads to useful selection criteria for the highdensity behavior of nuclear EoSs.

Article: Momentum, Density, and Isospin dependence of the Symmetric and Asymmetric Nuclear Matter Properties
[Show abstract] [Hide abstract] ABSTRACT: Properties of symmetric and asymmetric nuclear matter have been investigated in the relativistic DiracBruecknerHartreeFock approach based on projection techniques using the Bonn A potential. The momentum, density, and isospin dependence of the optical potentials and nucleon effective masses are studied. It turns out that the isovector optical potential depends sensitively on density and momentum, but is almost insensitive to the isospin asymmetry. Furthermore, the Dirac mass $m^*_D$ and the nonrelativistic mass $m^*_{NR}$ which parametrizes the energy dependence of the single particle spectrum, are both determined from relativistic DiracBruecknerHartreeFock calculations. The nonrelativistic mass shows a characteristic peak structure at momenta slightly above the Fermi momentum $\kf$. The relativistic Dirac mass shows a protonneutron mass splitting of $m^*_{D,n} <m^*_{D,p}$ in isospin asymmetric nuclear matter. However, the nonrelativistic mass has a reversed mass splitting $m^*_{NR,n} >m^*_{NR,p}$ which is in agreement with the results from nonrelativistic calculations. Comment: 25 pages, 12 figures, to appear in Physical Review C  [Show abstract] [Hide abstract] ABSTRACT: Relativistic and nonrelativistic modern nucleonnucleon potentials are mapped on a relativistic operator basis using projection techniques. This allows to compare the various potentials at the level of covariant amplitudes were a remarkable agreement is found. In nuclear matter large scalar and vector mean fields of several hundred MeV magnitude are generated at tree level. This is found to be a model independent feature of the nucleonnucleon interaction. Comment: 5 pages, 2 figures, results for V_lowk added, to appear in PRC
 [Show abstract] [Hide abstract] ABSTRACT: The momentum and isospin dependence of the inmedium nucleon mass are studied. Two definitions of the effective mass, i.e., the Dirac mass m*D and the nonrelativistic mass m*NR which parametrizes the energy spectrum, are compared. Both masses are determined from relativistic DiracBruecknerHartreeFock calculations. The nonrelativistic mass shows a distinct peak around the Fermi momentum. The protonneutron mass splitting in isospin asymmetric matter is m*D,n<m*D,p and opposite for the nonrelativistic mass, i.e., m*NR,n>m*NR,p, which is consistent with nonrelativistic approaches.
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886  Citations  
87.76  Total Impact Points  
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Institutions

20052014

University of Tuebingen
 Institute of Physical and Theoretical Chemistry
Tübingen, BadenWürttemberg, Germany
