The quark-meson model is investigated for the two- and three-flavor case extended by contributions of vector mesons under conditions encountered in core-collapse supernova matter. Typical temperature ranges, densities and electron fractions, as found
in core-collapse supernova simulations, are studied by implementing charge neutrality and local beta-equilibrium with respect to weak interactions. Within this framework, we analyze the resulting phase diagram and equation of state (EoS) and investigate the impact of undetermined parameters of the model. The EoS turns out to be relatively independent on the entropy per baryon but there are significant changes when going from the two-flavor to the three-flavor case due to the nontrivial contribution from the strange quarks which stay massive even at high densities. While an increasing vector meson coupling constant leads to a substantial stiffening of the EoS, we find that the impact of changing the scalar meson mass is equally strong and results in a softening of the EoS for increasing values.
The recent measurement of two solar mass pulsars has initiated an intense discussion on its impact on our understanding of the high-density matter in the cores of neutron stars. A task force meeting was held from October 7-10, 2013 at the Frankfurt I
nstitute for Advanced Studies to address the presence of quark matter in these massive stars. During this meeting, the recent oservational astrophysical data and heavy-ion data was reviewed. The possibility of pure quark stars, hybrid stars and the nature of the QCD phase transition were discussed and their observational signals delineated.
The QCD phase diagram might exhibit a first order phase transition for large baryochemical potentials. We explore the cosmological implications of such a QCD phase transition in the early universe. We propose that the large baryon-asymmetry is dilute
d by a little inflation where the universe is trapped in a false vacuum state of QCD. The little inflation is stopped by bubble nucleation which leads to primordial production of the seeds of extragalactic magnetic fields, primordial black holes and gravitational waves. In addition the power spectrum of cold dark matter can be affected up to mass scales of a billion solar masses. The imprints of the cosmological QCD phase transition on the gravitational wave background can be explored with the future gravitational wave detectors LISA and BBO and with pulsar timing.
The implications of a QCD phase transition at high temperatures and densities for core-collapse supernovae are discussed. For a strong first order phase transition to quark matter, various scenarios have been put forward in the literature. Here, deta
iled numerical simulations including neutrino transport are presented, where it is found that a second shock wave due to the QCD phase transition emerges shortly after bounce. It is demonstrated that such a supernova banging twice results in a second peak in the antineutrino spectrum. This second peak is clearly detectable in present neutrino detectors for a galactic supernova.
Some recent developments concerning the role of strange quark matter for astrophysical systems and the QCD phase transition in the early universe are addressed. Causality constraints of the soft nuclear equation of state as extracted from subthreshol
d kaon production in heavy-ion collisions are used to derive an upper mass limit for compact stars. The interplay between the viscosity of strange quark matter and the gravitational wave emission from rotation-powered pulsars are outlined. The flux of strange quark matter nuggets in cosmic rays is put in perspective with a detailed numerical investigation of the merger of two strange stars. Finally, we discuss a novel scenario for the QCD phase transition in the early universe, which allows for a small inflationary period due to a pronounced first order phase transition at large baryochemical potential.
We discuss the impact of strange hadrons, in particular hyperons, on the gross features of compact stars and on core-collapse supernovae. Hyperons are likely to be the first exotic species which appears around twice normal nuclear matter density in t
he core of neutron stars. Their presence largely influences the mass-radius relation of compact stars, the maximum mass, the cooling of neutron stars, the stability with regard to the emission of gravitational waves from rotation-powered neutron stars and the possible early onset of the QCD phase transition in core-collapse supernovae. We outline also the constraints from subthreshold kaon production in heavy-ion collisions for the maximum possible mass of neutron stars.
The properties of compact stars made of massive bosons with a repulsive selfinteraction mediated by vector mesons are studied within the mean-field approximation and general relativity. We demonstrate that there exists a scaling property for the mass
-radius curve for arbitrary boson masses and interaction strengths which results in an universal mass-radius relation. The radius remains nearly constant for a wide range of compact star masses. The maximum stable mass and radius of boson stars are determined by the interaction strength and scale with the Landau mass and radius. Both, the maximum mass and the corresponding radius increase linearly with the interaction strength so that they can be radically different compared to the other families of boson stars where interactions are ignored.
The possible role of a first order QCD phase transition at nonvanishing quark chemical potential and temperature for cold neutron stars and for supernovae is delineated. For cold neutron stars, we use the NJL model with nonvanishing color superconduc
ting pairing gaps, which describes the phase transition to the 2SC and the CFL quark matter phases at high baryon densities. We demonstrate that these two phase transitions can both be present in the core of neutron stars and that they lead to the appearance of a third family of solution for compact stars. In particular, a core of CFL quark matter can be present in stable compact star configurations when slightly adjusting the vacuum pressure to the onset of the chiral phase transition from the hadronic model to the NJL model. We show that a strong first order phase transition can have strong impact on the dynamics of core collapse supernovae. If the QCD phase transition sets in shortly after the first bounce, a second outgoing shock wave can be generated which leads to an explosion. The presence of the QCD phase transition can be read off from the neutrino and antineutrino signal of the supernova.
The implications of the formation of strange quark matter in neutron stars and in core-collapse supernovae is discussed with special emphasis on the possibility of having a strong first order QCD phase transition at high baryon densities. If strange
quark matter is formed in core-collapse supernovae shortly after the bounce, it causes the launch of a second outgoing shock which is energetic enough to lead to a explosion. A signal for the formation of strange quark matter can be read off from the neutrino spectrum, as a second peak in antineutrinos is released when the second shock runs over the neutrinosphere.
The role of hypernuclear physics for the physics of neutron stars is delineated. Hypernuclear potentials in dense matter control the hyperon composition of dense neutron star matter. The three-body interactions of nucleons and hyperons determine the
stiffness of the neutron star equation of state and thereby the maximum neutron star mass. Two-body hyperon-nucleon and hyperon-hyperon interactions give rise to hyperon pairing which exponentially suppresses cooling of neutron stars via the direct hyperon URCA processes. Non-mesonic weak reactions with hyperons in dense neutron star matter govern the gravitational wave emissions due to the r-mode instability of rotating neutron stars.
