The Quest for the Nuclear Equation of State
The present status of the efforts to determine the nuclear equation of state from results of heavy ion reactions and from astrophysical observations is reviewed
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arXiv subjects
J. Schaffner-Bielich
Publications and source records attributed to J. Schaffner-Bielich.
Neutron stars within the SU(2) parity doublet model
The equation of state of beta-stable and charge neutral nucleonic matter is computed within the SU(2) parity doublet model in mean field and in the relativistic Hartree approximation. The mass of the chiral partner of the nucleon is assumed to be 1200 MeV. The transition to the chiral restored phase turns out to be a smooth crossover in all the cases considered, taking place at a baryon density of just $2ρ_0$. The mass-radius relations of compact stars are calculated to constrain the model parameters from the maximum mass limit of neutron stars. It is demonstrated that chiral symmetry starts to be restored, which in this model implies the appearance of the chiral partners of the nucleons, in the center of neutron stars. However, the analysis of the decay width of the assumed chiral partner of the nucleon poses limits on the validity of the present version of the model to describe vacuum properties.
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Signals of the QCD phase transition in core-collapse supernovae
We explore the implications of the QCD phase transition during the postbounce evolution of core-collapse supernovae. Using the MIT bag model for the description of quark matter and assuming small bag constants, we find that the phase transition occurs during the early postbounce accretion phase. This stage of the evolution can be simulated with general relativistic three-flavor Boltzmann neutrino transport. The phase transition produces a second shock wave that triggers a delayed supernova explosion. If such a phase transition happens in a future galactic supernova, its existence and properties should become observable as a second peak in the neutrino signal that is accompanied by significant changes in the energy of the emitted neutrinos. In contrast to the first neutronization burst, this second neutrino burst is dominated by the emission of anti-neutrinos because the electron-degeneracy is lifted when the second shock passes through the previously neutronized matter.
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Triaxial nuclear models and the outer crust of nonaccreting cold neutron stars
The properties and composition of the outer crust of nonaccreting cold neutron stars are studied by applying the model of Baym, Pethick, and Sutherland (BPS) and taking into account for the first time triaxial deformations of nuclei. Two theoretical nuclear models, Hartree-Fock plus pairing in the BCS approximation (HF-BCS) with Skyrme SLy6 parametrization and Hartree-Fock-Bogolyubov (HFB) with Gogny D1S force, are used to calculate the nuclear masses. The two theoretical calculations are compared concerning their neutron drip line, binding energies, magic neutron numbers, and the sequence of nuclei in the outer crust of nonaccreting cold neutron stars, with special emphasis on the effect of triaxial deformations. The BPS model is extended by the higher-order corrections for the atomic binding, screening, exchange and zero-point energies. The influence of the higher-order corrections on the sequence of the outer crust is investigated.
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Signals of the QCD Phase Transition in the Heavens
The modern phase diagram of strongly interacting matter reveals a rich structure at high-densities due to phase transitions related to the chiral symmetry of quantum chromodynamics (QCD) and the phenomenon of color superconductivity. These exotic phases have significant impacts on high-density astrophysics as the properties of neutron stars and the evolution of astrophysical systems as proto-neutron stars, core-collapse supernovae and neutron star mergers. Most recent pulsar mass measurements and constraints on neutron star radii are critically discussed. Astrophysical signals for exotic matter and phase transitions in high-density matter proposed recently in the literature are outlined. A strong first order phase transition leads to the emergence of a third family of compact stars besides white dwarfs and neutron stars. The different microphysics of quark matter results in an enhanced r-mode stability window for rotating compact stars compared to normal neutron stars. Future telescope and satellite data will allow to extract signals from phase transitions in dense matter in the heavens and will reveal properties of the phases of dense QCD. Spectral line profiles out of x-ray bursts will determine the mass-radius ratio of compact stars. Gravitational wave patterns from collapsing neutron stars or neutron star mergers will even be able to constrain the stiffness of the quark matter equation of state. Future astrophysical data can therefore provide a crucial cross-check to the exploration of the QCD phase diagram with the heavy-ion program of the CBM detector at the FAIR facility.
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Stability of CFL cores in Hybrid Stars
We study the equation state of strongly interacting quark matter within a NJL-like model in which the chiral condensates and the color superconducting gaps are computed self-consistently as a function of the baryon density. A vector interaction term is added to the Lagrangian in order to render the quark matter equation of state stiffer. For the low density hadronic phase we use a relativistic mean field model. The phase transition to quark matter is computed by a Maxwell construction. We show that stable CFL cores in hybrid stars are possible if the superconducting gap is sufficiently large. Moreover we find stable stellar configurations in which two phase transitions occur, a first transition from hadronic matter to 2SC quark matter and a second transition from 2SC quark matter to CFL quark matter.
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Cosmology of fermionic dark matter
We explore a model for a fermionic dark matter particle family which decouples from the rest of the partices when at least all standard model particles are in equilibrium. We calculate the allowed ranges for mass and chemical potential to be compatible with big bang nucleosynthesis (BBN) calculations and WMAP-data for a flat universe with dark energy. Futhermore we estimate the free streaming length for fermions and antifermions to allow comparison to large scale structure data (LLS). We find that for dark matter decoupling when all standard model particles are present even the least restrictive combined BBN calculation and WMAP results allow us to constrain the initial dark matter chemical potential to a highest value of 6.3 times the dark matter temperature. In this case the resulting mass range is at most 1.8 eV < m < 53 eV, where the upper bound scales linearly with the effective degrees of freedom at decoupling. From LSS we find that similar to ordinary warm dark matter models the particle mass has to be larger than approximately 500 eV (meaning the effective degrees of freedom at decoupling have to be > 1000) to be compatible with observations of the Ly alpha forest at high redshift, but still the dark matter chemical potential over temperature ratio can exceed unity.
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Pulsar kicks by anisotropic neutrino emission from quark matter in strong magnetic fields
We discuss a pulsar acceleration mechanism based on asymmetric neutrino emission from the direct quark Urca process in the interior of proto neutron stars. The anisotropy is caused by a strong magnetic field which polarises the spin of the electrons opposite to the field direction. Due to parity violation the neutrinos and anti-neutrinos leave the star in one direction accelerating the pulsar. We calculate for varying quark chemical potentials the kick velocity in dependence of the quark phase temperature and its radius. Ignoring neutrino quark scattering we find that within a quark phase radius of 10 km and temperatures larger than 5 MeV kick velocities of 1000km s$^{-1}$ can be reached very easily. On the other hand taking into account the small neutrino mean free paths it seems impossible to reach velocities higher than 100km s$^{-1}$ even when including effects from colour superconductivity where the neutrino quark interactions are suppressed.
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Pulsar kicks by anisotropic neutrino emission from quark matter
We discuss an acceleration mechanism for pulsars out of their supernova remnants based on asymmetric neutrino emission from quark matter in the presence of a strong magnetic field. The polarized electron spin fixes the neutrino emission from the direct quark Urca process in one direction along the magnetic field. We calculate the magnetic field strength which is required to polarize the electron spin as well as the required initial proto-neutron star temperature for a successfull acceleration mechanism. In addition we discuss the neutrino mean free paths in quark as well as in neutron matter which turn out to be very small. Consequently, the high neutrino interaction rates will wash out the asymmetry in neutrino emission. As a possible solution to this problem we take into account effects from colour superconductivity.
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Formation of Quark Phases in compact stars and their connection to Gamma-Ray-Bursts
We analyse the occurrence of quiescent times in the temporal structure of the Gamma-Ray-Bursts (GRBs) light curves. We show that if a long quiescent time is present, it is possible to divide the total duration of GRBs into three periods: the pre-quiescence emission, the quiescent time and the post-quiescence emission. We then discuss a model of the GRBs inner engine based on the formation of quark phases during the life of an hadronic star. Within this model the pre-quiescence emission is interpreted as due to the deconfinement of quark inside an hadronic star and the formation of 2SC quark matter. The post-quiescence emission is due to the conversion of 2SC into the Color-Flavor-Locking (CFL) phase. The temporal delay between these two processes is connected with the nucleation time of the CFL phase in the 2SC phase and it can be associated with the observed quiescent times in the GRBs light curves. The stability of CFL cores in compact stars is also discussed.
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Hypernuclear Physics and Compact Stars
Hypernuclear physics plays a decisive role for several features of compact star physics. I review the impact of hypernuclear potential depths, two-body hyperon-nucleon and hyperon three-body forces as well as hyperon-hyperon interactions on the maximum mass, the mass-radius relation, and cooling properties of neutron stars.
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Asymmetric neutrino emission in quark matter and pulsar kicks
The puzzling phenomenon of pulsar kicks, i.e. the observed large escape velocities of pulsars out of supernova remnants, is examined for compact stars with a strange quark matter core. The direct Urca process in quark matter is studied in the presence of a strong magnetic field. Conditions for an asymmetric emission of the produced neutrinos are worked out in detail, giving constraints on the temperature, the strength of the magnetic field and the electron chemical potential in the quark matter core. In addition, the neutrino mean free paths for quark matter and a possible hadronic mantle are considered.
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Neutron stars and quark stars: Two coexisting families of compact stars?
The mass-radius relation of compact stars is discussed with relation to the presence of quark matter in the core. The existence of a new family of compact stars with quark matter besides white dwarfs and ordinary neutron stars is outlined.
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In-medium properties of D-mesons at FAIR
We obtain the D-meson spectral density at finite temperature for the conditions of density and temperature expected at FAIR. We perform a self-consistent coupled-channel calculation taking, as a bare interaction, a separable potential model. The $Λ_c$ (2593) resonance is generated dynamically. We observe that the D-meson spectral density develops a sizeable width while the quasiparticle peak stays close to the free position. The consequences for the D-meson production at FAIR are discussed.
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D-mesons: In-medium effects at FAIR
The $D$-meson spectral density at finite temperature is obtained within a self-consistent coupled-channel approach. For the bare meson-baryon interaction, a separable potential is taken, whose parameters are fixed by the position and width of the $Λ_c (2593)$ resonance. The quasiparticle peak stays close to the free $D$-meson mass, indicating a small change in the effective mass for finite density and temperature. Furthermore, the spectral density develops a considerable width due to the coupled-channel structure. Our results indicate that the medium modifications for the $D$-mesons in nucleus-nucleus collisions at FAIR (GSI) will be dominantly on the width and not, as previously expected, on the mass.
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In-medium effects on the $K^-/K^+$ ratio at GSI
The in-medium modifications on the $K^-/K^+$ ratio produced at GSI are studied. Particular attention is paid to the properties of antikaons, which determine the chemical potential and temperature at freeze-out conditions. Different approaches have been considered: non-interacting $K^-$, on-shell self-energy and single-particle spectral density. We observe that the full off-shell approach reproduces the "broad-band equilibration" advocated by Brown being the spectral density crucial to explain an enhanced $K^-/K^+$ ratio.
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D-mesons in dense nuclear matter
The D-meson properties in dense nuclear matter are studied. The D-meson spectral density is obtained within the framework of a coupled-channel self-consistent calculation assuming, as bare meson-baryon interaction, a separable potential. The $Λ_c(2593)$ resonance is generated dynamically in our coupled-channel model. The medium modifications of the D-meson properties due to Pauli blocking and the dressing of D-mesons, nucleons and pions are also studied. We conclude that the self-consistent coupled-channel process reduces the in-medium effects on the D-meson compared to previous literature which do not considered the coupled-channel structure
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What is so special about strangeness in hot matter?
The production of strange particles in a hot medium as produced in collisions of heavy ions is considered one of the most important signals for the phase transition to a quark-gluon plasma. In the first part of this lecture, the theoretical description of strangeness production in hot matter is outlined for a gas of quarks and gluons and for a hadronic gas and its impact on the deconfinement phase transition. Then in the second part, constraints from the underlying chiral symmetry of Quantum Chromodynamics (QCD) are utilized to extract signals with strangeness for the chiral phase transition in hot matter.
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