Strange Dibaryons in Neutron Stars and in Heavy-Ion Collisions

The formation of dibaryons with strangeness are discussed for the interior of neutron stars and for central relativistic heavy-ion collisions. We derive limits for the properties of H-dibaryons from pulsar data. Signals for the formation of possible bound states with hyperons at BNL's Relativistic Heavy-Ion Collider (RHIC) are investigated by studying their weak decay patterns and production rates.Comment: 7 pages, 4 figures, invited talk given at the VII International Conference on Hypernuclear and Strange Particle Physics, Torino, Italy, October 23-27, 200

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 a significant impact on high-density astrophysics, such 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 be used 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

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.Comment: 22 pages, 9 figures, to be published as topical review for Journal of Physics

Strangelets and Strange Quark Matter

The properties of finite lumps of strange quark matter (strangelets) with emphasis on the two scenarios of producing strange matter in relativistic heavy ion collisions are summarized. As an outlook, the possibility of short-lived strange composites and charmed matter are discussed for coming heavy ion experiments.Comment: 8 pages, 3 figures, uses elsevier style and epsf.sty, invited talk given at the International Conference on Hypernuclear and Strange Particle Physics (HYP'97), October 13-18, Brookhaven National Laboratory, USA, to be published in Nuclear Physics

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.Comment: 6 pages, 3 figures, poster contribution at the conference "Nuclear Physics in Astrophysics III",Dresden,March 26-31,200

Phase diagram and nucleation in the Polyakov-loop-extended Quark-Meson truncation of QCD with the unquenched Polyakov-loop potential

Unquenching of the Polyakov-loop potential showed to be an important improvement for the description of the phase structure and thermodynamics of strongly-interacting matter at zero quark chemical potentials with Polyakov-loop extended chiral models. This work constitutes the first application of the quark backreaction on the Polyakov-loop potential at nonzero density. The observation is that it links the chiral and deconfinement phase transition also at small temperatures and large quark chemical potentials. The build up of the surface tension in the Polyakov-loop extended Quark-Meson model is explored by investigating the two and 2+1-flavour Quark-Meson model and analysing the impact of the Polyakov-loop extension. In general, the order of magnitude of the surface tension is given by the chiral phase transition. The coupling of the chiral and deconfinement transition with the unquenched Polyakov-loop potential leads to the fact that the Polyakov-loop contributes at all temperatures.Comment: 28 pages, 13 figures; version published in Phys. Rev.

Effects of Renormalizing the chiral SU(2) Quark-Meson-Model

We investigate the restoration of chiral symmetry at finite temperature in the SU(2) quark meson model where the mean field approximation is compared to the renormalized version for quarks and mesons. In a combined approach at finite temperature all the renormalized versions show a crossover transition. The inclusion of different renormalization scales leave the order parameter and the mass spectra nearly untouched, but strongly influence the thermodynamics at low temperatures and around the phase transition. We find unphysical results for the renormalized version of mesons and the combined one