Rafael Bán Jacobsen

ON THE CONFINED–DECONFINED PHASE TRANSITION IN NUCLEAR MATTER AND NEUTRON STARS

In this work we focus our study on the transition from hadron to deconfined quark matter, and we shall assume that the phase transition is first-order with two independent components, which are related to the local conservation of baryon number and the global conservation of electric charge. Relativistic effective theories are employed to describe the hadron and quark phase. Two different hadronic models are adopted: an adjustable model and the well known Boguta–Bodmer model. Deconfined phase is described employing the MIT bag model. Previous studies showed that the choice of the hadronic model as well as its parameters (including nucleon effective mass and hyperonic coupling schemes) have influence on phase transition properties. Our aim is to analyze if such results on phase transition play an important role on the modeling of neutron stars. To carry out such analysis, the Tolman–Oppenheimer–Volkoff equations are employed to determine the maximum mass for each combination of hadronic model and parameters.

ANALYZING HADRON-QUARK MATTER PHASE TRANSITION BY MACROSCOPIC PROPERTIES OF NEUTRON STARS

A complementary way to investigate the Hadron-Quark-Gluon Phase transition in heavy ion collisions is to analyze properties of dense astrophysical objects, i.e. neutron stars. A neutron star can be simply described as a giant nucleus. However, due to the enormous gravitational contraction, it can reach densities up to several times the density found in the Pb nucleus. This property allows the formation of a core made up of free quarks and gluons. Once this new phase is formed, the new state drastically changes the neutron star macroscopic properties, such as its mass and radius. In the present work, we follow a route opposite to the common sense, investigating the properties of the phase transition by analyzing neutron star properties of mass and radius. This observations can determine the density where the transition can occur or the order of the transition using some sort of reverse engineering. As a consequence, the values of the bag constant or the strong coupling constant can be inferred.

QUARK–GLUON PLASMA IN A BAG MODEL WITH A SOFT SURFACE

We analyze the implications of quantum hadrodynamics (QHD) and quantum chromodynamics (QCD) to model, respectively, two distinct phases of nuclear matter, a baryon–meson phase and a quark–gluon phase. We develop an equation of state (EoS) in the framework of a quark–meson coupling model for the hadron–meson phase using a new version of the fuzzy bag model with scalar–isoscalar, vector–isoscalar and vector–isovector meson–quark couplings and leptonic degrees of freedom as well as the constrains from chemical equilibrium, baryon number and electric charge conservation. We model the EoS for the QGP phase for asymptotically free massless quarks and gluons using the MIT approach and a temperature and baryon chemical potential dependent bag constant, B(T,μ), which allows an isentropic equilibrium phase transition from a QGP to a hadron gas as determined by thermodynamics. Our predictions yield the EoS and static global properties of neutron stars and protoneutron stars at low and moderate values of temperature. Our results are slightly modified in comparison to predictions based on the standard MIT bag model with a constant bag pressure B.

ON THE ROLE OF THE ADIABATIC INDEX IN THE STABILITY OF NEUTRON STARS

We study the influence of interaction strengths on nuclear properties and global static properties of neutron stars with emphasis on the adiabatic index, considering also the constraint of chemical equilibrium and charge neutrality. We develop an equation of state (EoS) in the framework of an extended effective QHD model using a parameterized phenomenological Lagrangian density containing the fundamental baryon octet, the σ, ω and ϱ meson fields and the lightest charged leptons. The results of our approach show that, for a small range of values of the baryon–meson coupling parameters, we can consistently describe nuclear matter and the structure of neutron stars. Our results indicate that in the energy density range above hyperon thresholds, the behavior of the adiabatic index is roughly comparable to the corresponding one in the case of an extreme relativistic hydrodynamical perfect fluid.