498 research outputs found
Extended Skyrme interaction (I): spin fluctuations in dense matter
Most of the Skyrme interactions are known to predict spin or isospin
instabilities beyond the saturation density of nuclear matter which contradict
predictions based on realistic interactions. A modification of the standard
Skyrme interaction is proposed so that the ferromagnetic instability is
removed. The new terms are density dependent and modify only the spin p-h
interaction in the case of spin-saturated system. Consequences for the nuclear
response function and neutrino mean free path are shown. The overall effect of
the RPA correlations makes dense matter more transparent for neutrino
propagation by a factor of 2 to 10 depending of the density.Comment: 6 pages, 5 Figs., 2 Tab
Nuclear symmetry energy and core-crust transition in neutron stars: a critical study
The slope of the nuclear symmetry energy at saturation density is pointed
out as a crucial quantity to determine the mass and width of neutron-star
crusts. This letter clarifies the relation between and the core-crust
transition. We confirm that the transition density is soundly correlated with
despite differences between models, and we propose a clear understanding of
this correlation based on a generalised liquid drop model. Using a large number
of nuclear models, we evaluate the dispersion affecting the correlation between
the transition pressure and . From a detailed analysis it is shown
that this correlation is weak due to a cancellation between different terms.
The correlation between the isovector coefficients and plays
a crucial role in this discussion
Nuclear Superfluidity and Cooling Time of Neutron-Star Crust
We analyse the effect of neutron superfluidity on the cooling time of inner crust matter in neutron stars, in the case of a rapid cooling of the core. The specific heat of the inner crust, which determines the thermal response of the crust, is calculated in the framework of HFB approach at finite temperature. The calculations are performed with two paring forces chosen to simulate the pairing properties of uniform neutron matter corresponding respectively to Gogny-BCS approximation and to many-body techniques including polarisation effects. Using a simple model for the heat transport across the inner crust, it is shown that the two pairing forces give very different values for the cooling time
Low densities in asymmetric nuclear matter
Version2, Paper + figures included, PTHAsymmetric nuclear matter is investigated in the low density region below the nuclear saturation density. Microscopic calculations based on the Dirac Brueckner Hartree-Fock (DBHF) approach with realistic nucleon-nucleon potentials are used to adjust a low density functional. This functional is constructed on a density expansion of the relativistic mean field theory which allows a clear interpretation of the role of the mesons to the equation of state. It is shown that a correction term should be added to the functional in order to take into account the effects beyond the mean field. Two functionals with different corrections are obtained. Those functionals converge to predict a reduction of the spinodal zone in asymmetric nuclear matter by about 15-20\% and an isoscalar unstable mode closer to the constant Z/A direction than the functional without correction
Microscopic calculation of neutrino mean free path inside hot neutron matter
We calculate the neutrino mean free path and the Equation of State of pure
neutron matter at finite temperature within a selfconsistent scheme based on
the Brueckner--Hartree--Fock approximation. We employ the nucleon-nucleon part
of the recent realistic baryon-baryon interaction (model NSC97e) constructed by
the Nijmegen group. The temperatures considered range from 10 to 80 MeV. We
report on the calculation of the mean field, the residual interaction and the
neutrino mean free path including short and long range correlations given by
the Brueckner--Hartree--Fock plus Random Phase Approximation (BHF+RPA)
framework. This is the first fully consistent calculation in hot neutron matter
dedicated to neutrino mean free path. We compare systematically our results to
those obtain with the D1P Gogny effective interaction, which is independent of
the temperature. The main differences between the present calculation and those
with nuclear effective interactions come from the RPA corrections to BHF (a
factor of about 8) while the temperature lack of consistency accounts for a
factor of about 2
A full quantal theory of one-neutron halo breakup reactions
We present a theory of one-neutron halo breakup reactions within the
framework of post-form distorted wave Born approximation wherein pure Coulomb,
pure nuclear and their interference terms are treated consistently in a single
setup. This formalism is used to study the breakup of one-neutron halo nucleus
11Be on several targets of different masses. We investigate the role played by
the pure Coulomb, pure nuclear and the Coulomb-nuclear interference terms by
calculating several reaction observables. The Coulomb-nuclear interference
terms are found to be important for more exclusive observables.Comment: 22 pages latex, 9 figures, submitted to Phy. Rev.
Cluster formation in asymmetric nuclear matter: semi-classical and quantal approaches
The nuclear-matter liquid-gas phase transition induces instabilities against
finite-size density fluctuations. This has implications for both
heavy-ion-collision and compact-star physics. In this paper, we study the
clusterization properties of nuclear matter in a scenario of spinodal
decomposition, comparing three different approaches: the quantal RPA, its
semi-classical limit (Vlasov method), and a hydrodynamical framework. The
predictions related to clusterization are qualitatively in good agreement
varying the approach and the nuclear interaction. Nevertheless, it is shown
that i) the quantum effects reduce the instability zone, and disfavor
short-wavelength fluctuations; ii) large differences appear bewteen the two
semi-classical approaches, which correspond respectively to a collisionless
(Vlasov) and local equilibrium description (hydrodynamics); iii) the
isospin-distillation effect is stronger in the local equilibrium framework; iv)
important variations between the predicted time-scales of cluster formation
appear near the borders of the instability region.Comment: 27 pages, 11 figures, Submitted to Nuclear Physics A, Nuclear Physics
A In press (2008
Nuclear response functions in homogeneous matter with finite range effective interactions
The question of nuclear response functions in a homogeneous medium is
examined. A general method for calculating response functions in the random
phase approximation (RPA) with exchange is presented. The method is applicable
for finite-range nuclear interactions. Examples are shown in the case of
symmetric nuclear matter described by a Gogny interaction. It is found that the
convergence of the results with respect to the multipole truncation is quite
fast. Various approximation schemes such as the Landau approximation, or the
Landau approximation for the exchange terms only, are discussed in comparison
with the exact results.Comment: 9 pages, 9 figure
On the validity of the Wigner-Seitz approximation in neutron star crust
The inner crust of neutron stars formed of nuclear clusters immersed in a
neutron sea has been widely studied in the framework of the Wigner-Seitz
approximation since the seminal work of Negele and Vautherin. In this article,
the validity of this approximation is discussed in the framework of the band
theory of solids. For a typical cell of Zr, present in the external
layers of the inner crust, it is shown that the ground state properties of the
neutron gas are rather well reproduced by the Wigner-Seitz approximation, while
its dynamical properties depend on the energy scale of the process of interest
or on the temperature. It is concluded that the Wigner-Seitz approximation is
well suited for describing the inner crust of young neutron stars and the
collapsing core of massive stars during supernovae explosions. However the band
theory is required for low temperature fluid dynamics.Comment: 7 pages, with figures - PTH, version
Phase diagram of neutron-rich nuclear matter and its impact on astrophysics
Dense matter as it can be found in core-collapse supernovae and neutron stars
is expected to exhibit different phase transitions which impact the matter
composition and equation of state, with important consequences on the dynamics
of core-collapse supernova explosion and on the structure of neutron stars. In
this paper we will address the specific phenomenology of two of such
transitions, namely the crust-core solid-liquid transition at sub-saturation
density, and the possible strange transition at super-saturation density in the
presence of hyperonic degrees of freedom. Concerning the neutron star
crust-core phase transition at zero and finite temperature, it will be shown
that, as a consequence of the presence of long-range Coulomb interactions, the
equivalence of statistical ensembles is violated and a clusterized phase is
expected which is not accessible in the grand-canonical ensemble. A specific
quasi-particle model will be introduced to illustrate this anomalous
thermodynamics and some quantitative results relevant for the supernova
dynamics will be shown. The opening of hyperonic degrees of freedom at higher
densities corresponding to the neutron stars core modifies the equation of
state. The general characteristics and order of phase transitions in this
regime will be analyzed in the framework of a self-consistent mean-field
approach.Comment: Invited Talk given at the 11th International Conference on
Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1,
2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference
Series (JPCS
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