Temporal correlator in YM^2_3 and reflection-positivity violation

We consider numerical data for the lattice Landau gluon propagator obtained at very large lattice volumes in three-dimensional pure SU(2) Yang-Mills gauge theory (YM^2_3). We find that the temporal correlator C(t) shows an oscillatory pattern and is negative for several values of t. This is an explicit violation of reflection positivity and can be related to gluon confinement. We also obtain a good fit for this quantity in the whole time interval using a sum of Stingl-like propagators.Comment: 3 pages, 1 figure, 1 table, presented by A.R. Taurines at the IX Hadron Physics and VII Relativistic Aspects of Nuclear Physics Workshops, Angra dos Reis, Rio de Janeiro, Brazil (March 28--April 3, 2004

Small quark stars in the chromodielectric model

Equations of state for strange quark matter in beta equilibrium at high densities are used to investigate the structure (mass and radius) of compact objects. The chromodielectric model is used as a general framework for the quark interactions, which are mediated by chiral mesons, $\sigma$ and $\vec \pi$, and by a confining chiral singlet dynamical field, $\chi$. Using a quartic potential for $\chi$, two equations of state for the same set of model parameters are obtained, one with a minimum at around the nuclear matter density $\rho_0$ and the other at $\rho \sim 5 \rho_0$. Using the latter equation of state in the Tolman-Oppenheimer-Volkoff equations we found solutions corresponding to compact objects with $R\sim 5 - 8$ km and $M\sim M_\odot$. The phenomenology of recently discovered X-ray sources is compatible with the type of quark stars that we have obtained.Comment: 8 pages, AIP macros; Talk delivered at the Pan American Advanced Studies Institute (PASI) Conference "New States of Matter in Hadronic Interactions", Campos do Jordao, Brazil, January 200

Metastable strange matter and compact quark stars

Strange quark matter in beta equilibrium at high densities is studied in a quark confinement model. Two equations of state are dynamically generated for the {\it same} set of model parameters used to describe the nucleon: one corresponds to a chiral restored phase with almost massless quarks and the other to a chiral broken phase. The chiral symmetric phase saturates at around five times the nuclear matter density. Using the equation of state for this phase, compact bare quark stars are obtained with radii and masses in the ranges $R\sim 5 - 8$ km and $M\sim M_\odot$. The energy per baryon number decreases very slowly from the center of the star to the periphery, remaining above the corresponding values for the iron or the nuclear matter, even at the edge. Our results point out that strange quark matter at very high densities may not be absolutely stable and the existence of an energy barrier between the two phases may prevent the compact quarks stars to decay to hybrid stars.Comment: to appear on J. Phys.

Positivity violation for the lattice Landau gluon propagator

We present explicit numerical evidence of reflection-positivity violation for the lattice Landau gluon propagator in three-dimensional pure SU(2) gauge theory. We use data obtained at very large lattice volumes (V = 80^3, 140^3) and for three different lattice couplings in the scaling region (beta = 4.2, 5.0, 6.0). In particular, we observe a clear oscillatory pattern in the real-space propagator C(t). We also verify that the (real-space) data show good scaling in the range t \in [0,3] fm and can be fitted using a Gribov-like form. The violation of positivity is in contradiction with a stable-particle interpretation of the associated field theory and may be viewed as a manifestation of confinement.Comment: 5 pages, 6 figures; minor modifications in the text and in the bibliograph

SU(2) Landau gluon propagator on a 140^3 lattice

We present a numerical study of the gluon propagator in lattice Landau gauge for three-dimensional pure-SU(2) lattice gauge theory at couplings beta = 4.2, 5.0, 6.0 and for lattice volumes V = 40^3, 80^3, 140^3. In the limit of large V we observe a decreasing gluon propagator for momenta smaller than p_{dec} = 350^{+ 100}_{- 50} MeV. Data are well fitted by Gribov-like formulae and seem to indicate an infra-red critical exponent kappa slightly above 0.6, in agreement with recent analytic results.Comment: 5 pages with 2 figures and 3 tables; added a paragraph on discretization effect

Warm stellar matter with deconfinement: application to compact stars

We investigate the properties of mixed stars formed by hadronic and quark matter in $\beta$-equilibrium described by appropriate equations of state (EOS) in the framework of relativistic mean-field theory. We use the non- linear Walecka model for the hadron matter and the MIT Bag and the Nambu-Jona-Lasinio models for the quark matter. The phase transition to a deconfined quark phase is investigated. In particular, we study the dependence of the onset of a mixed phase and a pure quark phase on the hyperon couplings, quark model and properties of the hadronic model. We calculate the strangeness fraction with baryonic density for the different EOS. With the NJL model the strangeness content in the mixed phase decreases. The calculations were performed for T=0 and for finite temperatures in order to describe neutron and proto-neutron stars. The star properties are discussed. Both the Bag model and the NJL model predict a mixed phase in the interior of the star. Maximum allowed masses for proto-neutron stars are larger for the NJL model ($\sim 1.9$ M$_{\bigodot}$) than for the Bag model ($\sim 1.6$ M$_{\bigodot}$).Comment: RevTeX,14 figures, accepted to publication in Physical Review

Third Yearly Activity Report

The calculation work performed during the 3rd project year in WP2 as well as the R&D activities carried out in WP3, WP4 and WP5 are described in this report. In addition, the work dedicated to the project management (WP1) as well as to WP6 regarding the dissemination/communication activities and the education/training program (e.g. the follow-up of the mobility program between different organizations in the consortium, training on simulation tools and activities accomplished by PhD/post-doctoral students) is also reported

Electrically charged compact stars and formation of charged black holes

We study the effect of electric charge in compact stars assuming that the charge distribution is proportional to the mass density. The pressure and the density of the matter inside the stars are large, and the gravitational field is intense. This indicates that electric charge and a strong electric field can also be present. The relativistic hydrostatic equilibrium equation, i.e., the Tolman-Oppenheimer-Volkoff equation, is modified in order to include electric charge. We perform a detailed numerical study of the effect of electric charge using a polytropic equation of state. We conclude that in order to see any appreciable effect on the phenomenology of the compact stars, the electric fields have to be huge (~ 10^{21} V/m), which implies that the total charge is Q ~ 10^{20} Coulomb. From the local effect of the forces experienced on a single charged particle, it is expected that each individual charged particle is quickly ejected from the star. This in turn produces a huge force imbalance, and the gravitational force overwhelms the repulsive Coulomb and fluid pressure forces. The star can then collapse to form a charged black hole before all the charge leaves the system.Comment: 10 pages, 9 figures, To appear in Phys Rev.