78 research outputs found
Neutron star equations of state with optical potential constraint
Nuclear matter and neutron stars are studied in the framework of an extended
relativistic mean-field (RMF) model with higher-order derivative and density
dependent couplings of nucleons to the meson fields. The derivative couplings
lead to an energy dependence of the scalar and vector self-energies of the
nucleons. It can be adjusted to be consistent with experimental results for the
optical potential in nuclear matter. Several parametrisations, which give
identical predictions for the saturation properties of nuclear matter, are
presented for different forms of the derivative coupling functions. The stellar
structure of spherical, non-rotating stars is calculated for these new
equations of state (EoS). A substantial softening of the EoS and a reduction of
the maximum mass of neutron stars is found if the optical potential constraint
is satisfied.Comment: 19 pages, 4 figure
Neutron skin thickness of heavy nuclei with -particle correlations and the slope of the nuclear symmetry energy
The formation of -particle clusters on the surface of heavy nuclei is
described in a generalized relativistic mean-field model with explicit cluster
degrees of freedom. The effects on the size of the neutron skin of Sn nuclei
and Pb are investigated as a function of the mass number and the
isospin-dependent part of the effective interaction, respectively. The
correlation of the neutron skin thickness with the difference of the neutron
and proton numbers and with the slope of the nuclear symmetry energy is
modified as compared to the mean-field calculation without alpha-cluster
correlations.Comment: 5 pages, 5 figures, 1 table, version accepted for publication in
Physical Review
Constraining supernova equations of state with equilibrium constants from heavy-ion collisions
Cluster formation is a fundamental aspect of the equation of state (EOS) of
warm and dense nuclear matter such as can be found in supernovae (SNe). Similar
matter can be studied in heavy-ion collisions (HIC). We use the experimental
data of Qin et al. [Phys. Rev. Lett. 108, 172701 (2012)] to test calculations
of cluster formation and the role of in-medium modifications of cluster
properties in SN EOSs. For the comparison between theory and experiment we use
chemical equilibrium constants as the main observables. This reduces some of
the systematic uncertainties and allows deviations from ideal gas behavior to
be identified clearly. In the analysis, we carefully account for the
differences between matter in SNe and HICs. We find that, at the lowest
densities, the experiment and all theoretical models are consistent with the
ideal gas behavior. At higher densities ideal behavior is clearly ruled out and
interaction effects have to be considered. The contributions of continuum
correlations are of relevance in the virial expansion and remain a difficult
problem to solve at higher densities. We conclude that at the densities and
temperatures discussed mean-field interactions of nucleons, inclusion of all
relevant light clusters, and a suppression mechanism of clusters at high
densities have to be incorporated in the SN EOS.Comment: 20 pages, 15 figures, v2: matches published version, only minor
editorial correction
Electromagnetic Dissociation as a Tool for Nuclear Structure and Astrophysics
Coulomb dissociation is an especially simple and important reaction
mechanism. Since the perturbation due to the electric field of the nucleus is
exactly known, firm conclusions can be drawn from such measurements.
Electromagnetic matrix elements and astrophysical S-factors for radiative
capture processes can be extracted from experiments. We describe the basic
theory, new results concerning higher order effects in the dissociation of
neutron halo nuclei, and briefly review the experimental results obtained up to
now. Some new applications of Coulomb dissociation for nuclear astrophysics and
nuclear structure physics are discussed.Comment: 10 pages, 1 figure, to appear in Proceedings of the International
School on Nuclear Physics; 22nd Course: ``Radioactive Beams for Nuclear and
Astro Physics'', Erice/Sicily/Italy, September 16 - 24, 200
Light clusters in nuclear matter: Excluded volume versus quantum many-body approaches
The formation of clusters in nuclear matter is investigated, which occurs
e.g. in low energy heavy ion collisions or core-collapse supernovae. In
astrophysical applications, the excluded volume concept is commonly used for
the description of light clusters. Here we compare a phenomenological excluded
volume approach to two quantum many-body models, the quantum statistical model
and the generalized relativistic mean field model. All three models contain
bound states of nuclei with mass number A <= 4. It is explored to which extent
the complex medium effects can be mimicked by the simpler excluded volume
model, regarding the chemical composition and thermodynamic variables.
Furthermore, the role of heavy nuclei and excited states is investigated by use
of the excluded volume model. At temperatures of a few MeV the excluded volume
model gives a poor description of the medium effects on the light clusters, but
there the composition is actually dominated by heavy nuclei. At larger
temperatures there is a rather good agreement, whereas some smaller differences
and model dependencies remain.Comment: 12 pages, 6 figures, published version, minor change
Lagrange-Mesh Method for Deformed Nuclei With Relativistic Energy Density Functionals
The application of relativistic energy density functionals to the description of nuclei leads to the problem of solving self-consistently a coupled set of equations of motion to determine the nucleon wave functions and meson fields. In this work, the Lagrange-mesh method in spherical coordinates is proposed for numerical calculations. The essential field equations are derived from the relativistic energy density functional and the basic principles of the Lagrange-mesh method are delineated for this particular application. The numerical accuracy is studied for the case of a deformed relativistic harmonic oscillator potential with axial symmetry. Then the method is applied to determine the point matter distributions and deformation parameters of self-conjugate even-even nuclei from âŽHe to âŽâ°Ca
Exploring thermal effects of the hadron-quark matter transition in neutron star mergers
We study the importance of the thermal behavior of the hadron-quark phase
transition in neutron star (NS) mergers. To this end, we devise a new scheme
approximating thermal effects to supplement any cold, barotropic hybrid
equation of state (EoS) model, i.e. two-phase EoS constructions with a hadronic
regime and a phase of deconfined quark matter. The consideration of
temperature-dependent phase boundaries turns out to be critical for a
quantitative description of quark matter effects in NS mergers, since the
coexistence phase can introduce a strong softening of the EoS at finite
temperature, which is even more significant than the change of the EoS by the
phase transition at T=0. We validate our approach by comparing to existing
fully temperature-dependent EoS models and find a very good quantitative
agreement of postmerger gravitational-wave (GW) features. Simulations with the
commonly-used thermal ideal-gas approach exhibit sizable differences compared
to full hybrid models implying that its use in NS merger simulations with quark
matter is problematic. Our new scheme provides the means to isolate thermal
effects of quark matter from the properties of the cold hybrid EoS and thus
allows an assessment of the thermal behavior alone. We show that different
shapes of the phase boundaries at finite temperature can have a large impact on
the postmerger dynamics and GW signal for the same cold hybrid model. This
finding demonstrates that postmerger GW emission contains important
complementary information compared to properties extracted from cold stars. We
also show by concrete examples that it is even possible for quark matter to
only occur and thus be detectable in finite-temperature systems like merger
remnants but not in cold NSs (abbreviated).Comment: 28 pages, 16 figures, revised version, published by Phys. Rev.
Equations of state for supernovae and compact stars
A review is given of various theoretical approaches for the equation of state (EoS) of dense matter, relevant for the description of core-collapse supernovae, compact stars, and compact star mergers. The emphasis is put on models that are applicable to all of these scenarios. Such EoS models have to cover large ranges in baryon number density, temperature, and isospin asymmetry. The characteristics of matter change dramatically within these ranges, from a mixture of nucleons, nuclei, and electrons to uniform, strongly interacting matter containing nucleons, and possibly other particles such as hyperons or quarks. As the development of an EoS requires joint efforts from many directions, different theoretical approaches are considered and relevant experimental and observational constraints which provide insights for future research are discussed. Finally, results from applications of the discussed EoS models are summarized
How Well Do We Know The Supernova Equation of State?
We give an overview about equations of state (EOS) which are currently available for simulations of core-collapse supernovae and neutron star mergers. A few selected important aspects of the EOS, such as the symmetry energy, the maximum mass of neutron stars, and cluster formation, are confronted with constraints from experiments and astrophysical observations. There are just very few models which are compatible even with this very restricted set of constraints. These remaining models illustrate the uncertainty of the uniform nuclear matter EOS at high densities. In addition, at finite temperatures the medium modifications of nuclear clusters represent a conceptual challenge. In conclusion, there has been significant development in the recent years, but there is still need for further improved general purpose EOS tables
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