ABSTRACT
The transition from hadronic to quark matter at high density is a strong first order phase transition if the surface tension between the two phases is large. While this implies a constant-pressure mixed phase in cold neutron star matter this is not the case for the hot and lepton rich matter of protoneutron stars. By considering the global conservation of lepton number during the stage of neutrino trapping, we show that a new mixed phase with non-constant pressure could appear in protoneutron stars and it would gradually disappear during deleptonization. We discuss the peculiar properties of this mixed phase and its possible significant effects on the evolution of protoneutron stars and their neutrino emission.
ABSTRACT
We determine the Galactic production rate of strangelets as a canonical input to calculations of the measurable cosmic ray flux of strangelets by performing simulations of strange star mergers and combining the results with recent estimates of stellar binary populations. We find that the flux depends sensitively on the bag constant of the MIT bag model of QCD and disappears for high values of the bag constant and thus more compact strange stars. In the latter case, strange stars could coexist with ordinary neutron stars as they are not converted by the capture of cosmic ray strangelets. An unambiguous detection of an ordinary neutron star would then not rule out the strange matter hypothesis.
ABSTRACT
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, we model phase transitions that occur during the early postbounce evolution. 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. This second neutrino burst is dominated by the emission of antineutrinos because the electron degeneracy is reduced when the second shock passes through the previously neutronized matter.
ABSTRACT
In a theoretical interpretation of observational data from the neutron star EXO 0748-676, Ozel concludes that quark matter probably does not exist in the centre of neutron stars. However, this conclusion is based on a limited set of possible equations of state for quark matter. Here we compare Ozel's observational limits with predictions based on a more comprehensive set of proposed quark-matter equations of state from the literature, and conclude that the presence of quark matter in EXO 0748-676 is not ruled out.
ABSTRACT
The effective restoration of the chiral U(A)(1) symmetry in strong interactions is studied using the linear chiral SU(3)xSU(3) model at finite temperatures. We find that the disappearance of the chiral anomaly causes a considerable change in the meson mass spectrum. We propose several signals for detecting this chiral phase in ultrarelativistic heavy-ion collisions: The eta/pi(0) ratio is enhanced by an order of magnitude, the a(0) is suppressed in the K&Kmacr; mass spectrum, and the scalar kappa meson appears as a peak just below the K(*)(892) in the invariant piK mass spectrum.
ABSTRACT
Weak SU(3) symmetry is successfully applied to the weak hadronic decay amplitudes of octet hyperons. Weak nonmesonic and mesonic decays of various dibaryons with strangeness, their dominant decay modes, and lifetimes are calculated. Production estimates for the Brookhaven Relativistic Heavy Ion Collider are presented employing wave-function coalescence. Signals for detecting strange dibaryon states in heavy-ion collisions and revealing information about the unknown hyperon-hyperon interactions are outlined.
