Showing papers on "Nuclear matter published in 2006"

Neutron Star Observations: Prognosis for Equation of State Constraints

Abstract: We investigate how current and proposed observations of neutron stars can lead to an understanding of the state of their interiors and the key unknowns: the typical neutron star radius and the neutron star maximum mass. A theoretical analysis of neutron star structure, including general relativistic limits to mass, compactness, and spin rates is made. We consider observations made not only with photons, ranging from radio waves to X-rays, but also those involving neutrinos and gravity waves. We detail how precision determinations of structural properties would lead to significant restrictions on the poorly understood equation of state near and beyond the equilibrium density of nuclear matter.

Constraints on the high-density nuclear equation of state from the phenomenology of compact stars and heavy-ion collisions

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 heavy-ion 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 heavy-ion collisions. Compact star constraints include the mass

Deducing the nuclear-matter incompressibility coefficient from data on isoscalar compression modes

Abstract: Accurate assessment of the value of the incompressibility coefficient, K, of symmetric nuclear matter, which is directly related to the curvature of the equation of state (EOS), is needed to extend our knowledge of the EOS in the vicinity of the saturation point. We review the current status of K as determined from experimental data on isoscalar giant monopole and dipole resonances (compression modes) in nuclei, by employing the microscopic theory based on the random-phase approximation (RPA).

The Skyrme Interaction in finite nuclei and nuclear matter

Abstract: Self-consistent mean-field models are a powerful tool in the investigation of nuclear structure and low-energy dynamics. They are based on effective energy-density functionals, often formulated in terms of effective density-dependent nucleon-nucleon interactions. The free parameters of the functional are adjusted to empirical data. A proper choice of these parameters requires a comprehensive set of constraints covering experimental data on finite nuclei, concerning static as well as dynamical properties, empirical characteristics of nuclear matter, and observational information on nucleosynthesis, neutron stars and supernovae. This work aims at a comprehensive survey of the performance of one of the most successful non-relativistic self-consistent method, the Skyrme-Hartree-Fock model (SHF), with respect to these constraints. A full description of the Skyrme functional is given and its relation to other effective interactions is discussed. The validity of the application of SHF far from stability and in dense environments beyond the nuclear saturation density is critically assessed. The use of SHF in models extended beyond the mean field approximation by including some correlations is discussed. Finally, future prospects for further development of SHF towards a more consistent application of the existing and promisingly newly developing constraints are outlined.

Hindrance of heavy-ion fusion due to nuclear incompressibility

Abstract: We propose a new mechanism to explain the unexpected steep falloff of fusion cross sections at energies far below the Coulomb barrier. The saturation properties of nuclear matter are causing a hindrance to large overlap of the reacting nuclei and consequently a sensitive change of the nuclear potential inside the barrier. We report in this Letter a good agreement with the data of coupled-channels calculation for the {sup 64}Ni+{sup 64}Ni combination using the double-folding potential with Michigan-3-Yukawa-Reid effective N-N forces supplemented with a repulsive core that reproduces the nuclear incompressibility for total overlap.

Screening effects in superfluid nuclear and neutron matter within Brueckner theory

Abstract: Effects of medium polarization are studied for ${}^{1}{S}_{0}$ pairing in neutron and nuclear matter. The screening potential is calculated in the RPA limit, suitably renormalized to cure the low density mechanical instability of nuclear matter. The self-energy corrections are consistently included resulting in a strong depletion of the Fermi surface. All medium effects are calculated based on the Brueckner theory. The ${}^{1}{S}_{0}$ gap is determined from the generalized gap equation. The self-energy corrections always lead to a quenching of the gap, which is enhanced by the screening effect of the pairing potential in neutron matter, whereas it is almost completely compensated by the antiscreening effect in nuclear matter.

Recent results in relativistic heavy ion collisions: from ‘a new state of matter’ to ‘the perfect fluid’

Abstract: Experimental physics with relativistic heavy ions dates from 1992 when a beam of 197Au of energy greater than 10 A?GeV/c first became available at the Alternating Gradient Synchrotron at Brookhaven National Laboratory (BNL) soon followed in 1994 by a 208Pb beam of 158A?GeV/c at the Super Proton Synchrotron at CERN (European Center for Nuclear Research). Previous pioneering measurements at the Berkeley Bevalac (Gutbrod et al 1989 Rep. Prog. Phys. 52 1267?132) in the late 1970s and early 1980s were at much lower bombarding energies (1A?GeV/c) where nuclear breakup rather than particle production is the dominant inelastic process in A+A collisions. More recently, starting in 2000, the relativistic heavy ion collider at BNL has produced head-on collisions of two 100 A?GeV beams of fully stripped Au ions, corresponding to nucleon?nucleon centre-of-mass (cm) energy, , total cm energy 200 A?GeV. The objective of this research program is to produce nuclear matter with extreme density and temperature, possibly resulting in a state of matter where the quarks and gluons normally confined inside individual nucleons (r < 1?fm) are free to act over distances an order of magnitude larger. Progress from the period 1992 to the present will be reviewed, with reference to previous results from light ion and proton?proton collisions where appropriate. Emphasis will be placed on the measurements which formed the basis for the announcements by the two major laboratories: 'A new state of matter', by CERN on Febraury 10 2000 and 'The perfect fluid' by BNL on April 19 2005.

Nuclear matter saturation point and symmetry energy with modern nucleon-nucleon potentials

Abstract: We determine the saturation properties of nuclear matter within the Brueckner-Hartree-Fock approach based on a large set of modern nucleon-nucleon potentials and confirm the validity of the Coester band. The improvement of the saturation point when including nuclear three-body forces is pointed out and comparison with the Dirac-Brueckner-Hartree-Fock results is made.

D Mesons in Nuclear Matter: A DN Coupled-Channel Equations Approach

Abstract: A set of coupled two-body scattering equations is solved for the DN system embedded in an isosymmetric nuclear matter. The in-medium behavior of charmed D mesons, (D + ,D 0 ), is investigated from the self-consistent solution within this scheme. The effective meson-baryon Lagrangian in charm quantum number one sector, the key ingredient in the present study, is adopted from a recent model by Hofmann and Lutz that has aimed at combining the charmed meson degree of freedom in a consistent manner with chiral unitary models. After a critical examination, the original model is modified in several important aspects, such as the method of regularization, to be more consistent and practical for our objective. The resultant interaction is used to reproduce � ¯

From Brueckner approach to Skyrme-type energy density functional

Abstract: A Skyrme-like effective interaction is built up from the equation of state of nuclear matter. The latter is calculated in the framework of the Brueckner-Hartree-Fock approximation with two- and three-body forces. A complete Skyrme parametrization requires a fit of the neutron and proton effective masses and the Landau parameters. The new parametrization is probed on the properties of a set of closed-shell and closed-subshell nuclei, including binding energies and charge radii.

Isovector splitting of nucleon effective masses, ab-initio benchmarks and extended stability criteria for Skyrme energy functionals

Abstract: We study the effect of the splitting of neutron and proton effective masses with isospin asymmetry on the properties of the Skyrme energy density functional. We discuss the ability of the latter to predict observables of infinite matter and finite nuclei, paying particular attention to controlling the agreement with ab initio predictions of the spin-isospin content of the nuclear equation of state, as well as diagnosing the onset of finite size instabilities, which we find to be of critical importance. We show that these various constraints cannot be simultaneously fulfilled by the standard Skyrme force, calling at least for an extension of its $P$-wave part.

Phase transitions in the early and the present Universe

Abstract: The evolution of the Universe is the ultimate laboratory to study fundamental physics across energy scales that span about 25 orders of magnitude: from the grand unification scale through particle and nuclear physics scales down to the scale of atomic physics. The standard models of cosmology and particle physics provide the basic understanding of the early and present Universe and predict a series of phase transitions that occurred in succession during the expansion and cooling history of the Universe. We survey these phase transitions, highlighting the equilibrium and non-equilibrium effects as well as their observational and cosmological consequences. We discuss the current theoretical and experimental programs to study phase transitions in QCD and nuclear matter in accelerators along with the new results on novel states of matter as well as on multi- fragmentation in nuclear matter. A critical assessment of similarities and differences between the conditions in the early universe and those in ultra- relativistic heavy ion collisions is presented. Cosmological observations and accelerator experiments are converging towards an unprecedented understanding of the early and present Universe.

Chiral approach to antikaon s - and p -wave interactions in dense nuclear matter

Abstract: The properties of the antikaons in nuclear matter are investigated from a chiral unitary approach which incorporates the $s$- and $p$-waves of the $\overline{K}N$ interaction. To obtain the in-medium meson-baryon amplitudes we include, in a self-consistent way, Pauli blocking effects, meson self-energies corrected by nuclear short-range correlations and baryon binding potentials. We pay special attention to investigating the validity of the on-shell factorization, showing that it cannot be applied in the evaluation of the in-medium corrections to the $p$-wave amplitudes. In nuclear matter at saturation energy, the \ensuremath{\Lambda} and \ensuremath{\Sigma} develop an attractive potential of about \ensuremath{-}30 MeV, while the ${\ensuremath{\Sigma}}^{*}$ pole remains at the free space value although its width gets sensibly increased to about 80 MeV. The antikaon also develops a moderate attraction that does not support the existence of very deep and narrow bound states, confirming the findings of previous self-consistent calculations.

Exploring the extended density-dependent Skyrme effective forces for normal and isospin-rich nuclei to neutron stars

Abstract: We parametrize the recently proposed generalized Skyrme effective force (GSEF) containing extended density dependence. The parameters of the GSEF are determined by the fit to several properties of the normal and isospin-rich nuclei. We also include in our fit a realistic equation of state for the pure neutron matter up to high densities so that the resulting Skyrme parameters can be suitably used to model the neutron star with the 'canonical' mass ({approx}1.4M{sub {center_dot}}). For the appropriate comparison, we generate a parameter set for the standard Skyrme effective force (SSEF) using exactly the same set data as employed to determine the parameters of the GSEF. We find that the GSEF yields larger values for the neutron skin thickness which are closer to the recent predictions based on the isospin diffusion data. The Skyrme parameters so obtained are employed to compute the strength function for the isoscalar giant monopole, dipole, and quadrupole resonances. It is found that in the case of GSEF, because of the larger value of the nucleon effective mass, the values of centroid energies for the isoscalar giant resonances are in better agreement with the corresponding experimental data than those obtained using the SSEF. We also present resultsmore » for some of the key properties associated with the neutron star of canonical mass and for the one with the maximum mass.« less

Entrainment parameters in a cold superfluid neutron star core

Abstract: Hydrodynamic simulations of neutron star cores that are based on a two-fluid description in terms of a neutron-proton superfluid mixture require the knowledge of the Andreev-Bashkin entrainment matrix which relates the momentum of one constituent to the currents of both constituents. This matrix is derived for arbitrary nuclear asymmetry at zero temperature and in the limits of small relative currents in the framework of the energy density functional theory. The Skyrme energy density functional is considered as a particular case. General analytic formulas for the entrainment parameters and various corresponding effective masses are obtained. These formulas are applied to the liquid core of a neutron star composed of homogeneous plasma of nucleons, electrons, and possibly muons in \ensuremath{\beta} equilibrium.

Mach cones in an evolving medium

Abstract: The energy and momentum lost by a hard parton propagating through hot and dense matter has to be redistributed in the nuclear medium. Apart from heating the medium, there is the possibility that collective modes are excited. We outline a formalism that can be used to track the propagation of such a mode through the evolving medium if its dispersion relation is known. Under the assumption that a sound wave is created, we track the jet energy loss as a function of spacetime and follow the resulting mach cone throughout the fireball evolution. We compare with the angular correlation pattern of hard hadrons as obtained by the PHENIX Collaboration and find good agreement with the data provided that a substantial fraction of jet energy (\ensuremath{\sim}90%) is deposited into a propagating mode and that the hot matter can be characterized by an equation of state with a soft point (not necessarily a mixed phase).

Anomalous Transport Processes in Anisotropically Expanding Quark-Gluon Plasmas

Abstract: We derive an expression for the anomalous viscosity in an anisotropically expanding quark-gluon-plasma, which arises from interactions of thermal partons with dynamically generated color fields. The anomalous viscosity dominates over the collisional viscosity for large velocity gradients or weak coupling. This effect may provide an explanation for the apparent “nearly perfect” liquidity of the matter produced in nuclear collisions at RHIC without the assumption that it is a strongly coupled state.

Hybrid protoneutron stars with the MIT bag model

Abstract: We study the hadron-quark phase transition in the interior of protoneutron stars. For the hadronic sector, we use a microscopic equation of state involving nucleons and hyperons derived within the finite-temperature Brueckner-Bethe-Goldstone many-body theory, with realistic two-body and three-body forces. For the description of quark matter, we employ the MIT bag model both with a constant and a density-dependent bag parameter. We calculate the structure of protostars with the equation of state comprising both phases and find maximum masses below 1.6 solar masses. Metastable heavy hybrid protostars are not found.

Lattice QCD constraints on the nuclear equation of state

Abstract: Based on the quasi-particle description of the QCD medium at finite temperature and density we formulate the phenomenological model for the equation of state that exhibits crossover or the first-order deconfinement phase transition. The models are constructed in such a way as to be thermodynamically consistent and to satisfy the properties of the ground state nuclear matter complying with constraints from intermediate heavy-ion collision data. Our equations of states show a quite reasonable agreement with the recent lattice findings on the temperature and baryon chemical potential dependence of relevant thermodynamical quantities in the parameter range covering both the hadronic and quark–gluon sectors. The model predictions on the isentropic trajectories in the phase diagram are shown to be consistent with the recent lattice results. Our nuclear equations of state are to be considered as an input to the dynamical models describing the production and the time evolution of a thermalized medium created in heavy-ion collisions in a broad energy range from SIS up to LHC.

Cold dilute neutron matter on the lattice II: Results in the unitary limit

Abstract: This is the second of two articles that investigate cold dilute neutron matter on the lattice using pionless effective field theory. In the unitary limit, where the effective range is zero and scattering length is infinite, simple scaling relations relate thermodynamic functions at different temperatures. When the second virial coefficient is properly tuned, we find that the lattice results obey these scaling relations. We compute the energy per particle, pressure, spin susceptibility, dineutron correlation function, and an upper bound for the superfluid critical temperature.

Dirac-Brueckner-Hartree-Fock calculations for isospin asymmetric nuclear matter based on improved approximation schemes

Abstract: We present Dirac-Brueckner-Hartree-Fock 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 proton-neutron 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 Dirac-Brueckner-Hartree-Fock equation of state requires a renormalization of these coupling functions.