7,170 research outputs found
Modeling Hybrid Stars
We study the so called hybrid stars, which are hadronic stars that contain a
core of deconfined quarks. For this purpose, we make use of an extended version
of the SU(3) chiral model. Within this approach, the degrees of freedom change
naturally from hadrons (baryon octet) to quarks (u, d, s) as the temperature
and/or density increases. At zero temperature we are still able to reproduce
massive stars, even with the inclusion of hyperons.Comment: To appear in the proceedings of Conference C12-08-0
The application of the Quark-Hadron Chiral Parity-Doublet Model to neutron star matter
The Quark-Hadron Chiral Parity-Doublet model (QP) is applied to
calculate compact star properties in the presence of a deconfinement phase
transition. Within this model, a consistent description of nuclear matter
properties, chiral symmetry restoration, and a transition from hadronic to
quark and gluonic degrees of freedom is possible within one unified approach.
We find that the equation of state obtained is consistent with recent
perturbative quantum chromodynamics (QCD) results and is able to accommodate
observational constraints of massive and small neutron stars. Furthermore, we
show that important features of the equation of state, such as the symmetry
energy and its slope, are well within their observational constraints.Comment: 8 pages, 9 figures and 1 tabl
Chiral Hadronic Mean Field Model including Quark Degrees of Freedom
In an approach inspired by Polyakov loop extended NJL models, we present a
nonlinear hadronic SU(3) sigma-omega mean field model augmented by quark
degrees of freedom. By introducing the effective Polyakov loop related scalar
field \Phi and an associated effective potential, the model includes all known
hadronic degrees of freedom at low temperatures and densities as well as a
quark phase at high temperatures and densities. Hadrons in the model exhibit a
finite volume in order to suppress baryons at high T and \mu. This ensures that
the right asymptotic degrees of freedom are attained for the description of
strongly interacting matter and allows to study the QCD phase diagram in a wide
range of temperatures and chemical potentials. Therefore, with this model it is
possible to study the phase transition of chiral restoration and deconfinement.
In this paper, the impact of quarks on the resulting phase diagram is shown.
The results from the chiral model are compared to recent data from lattice QCD.Comment: 25 pages, 10 figure
The Structure and Clustering of Lyman Break Galaxies
The number density and clustering properties of Lyman-break galaxies (LBGs)
are consistent with them being the central galaxies of the most massive dark
halos present at z~3. This conclusion holds in all currently popular
hierarchical models for structure formation, and is almost independent of the
global cosmological parameters. We examine whether the sizes, luminosities,
kinematics and star-formation rates of LBGs are also consistent with this
identification. Simple formation models tuned to give good fits to low redshift
galaxies can predict the distribution of these quantities in the LBG
population. The LBGs should be small (with typical half-light radii of 0.6-2
kpc/h), should inhabit haloes of moderately high circular velocity (180-290
km/s) but have low stellar velocity dispersions (70-120 km/s) and should have
substantial star formation rates (15-100 Msun/yr). The numbers here refer to
the predicted median values in the LBG sample of Adelberger et al. (1998); the
first assumes an Omega=1 universe and the second a flat universe with
Omega=0.3. For either cosmology these predictions are consistent with the
current (rather limited) observational data. Following the work of Kennicutt
(1998) we assume stars to form more rapidly in gas of higher surface density.
This predicts that LBG samples should preferentially contain objects with low
angular momentum, and so small size, for their mass. In contrast, samples of
damped Lyman alpha systems (DLSs), should be biased towards objects with large
angular momentum. Bright LBGs and DLSs may therefore form distinct populations,
with very different sizes and star formation rates, LBGs being smaller and more
metal-rich than DLSs of similar mass and redshift.Comment: 27 pages, 9 figures, MNRAS submitte
Properties and Stability of Hybrid Stars
We discuss the properties of neutron stars and their modifications due to the
occurrence of hyperons and quarks in the core of the star. More specifically,
we consider the general problem of exotic particles inside compact stars in
light of the observed two-solar mass pulsar. In addition, we investigate
neutron star cooling and a possible explanation of the recently measured
cooling curve of the neutron star in the supernova remnant Cas A.Comment: Contribution to SQM 2011 in Krak\'o
- …