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[en] Full text: The knowledge gained from studies of nuclear physics is fundamental to the whole process of stellar evolution is better understood. In this paper we study and describe some of the physical characteristics of the interior of neutron stars, pulsars and magnetars on studying how the inclusion of a strong magnetic field and the entire baryon octet alter the physical characteristics of these objects, such as mass, radius, and to understand how the chemical composition varies with the density. Begin with a very simple system, which is a gas of free neutrons that counterbalances the gravitational force only by degeneracy pressure, which stems from the Pauli exclusion principle. From the calculation of energy density and pressure, we obtain our equations of state, and with them we obtain by solving the Oppenheimer-Volkoff equations, our estimate of the mass and radius. After that, in order to let our star more realistic, add protons and electrons, imposing to the star chemical equilibrium and zero total charge. Finally we extend our beta equilibrium and charge neutrality by adding the entire baryon octet as well as muons. Once done, we left the formalism of free Fermi gas and include a magnetic field, this causes appear so-called Landau levels and then study how this magnetic field changes the equations of state and consequently their physical characteristics. To describe the physical interactions between the hadrons we use the effective Walleck linear and nonlinear models. This phase of work is still in development. (author)

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[en] Full text: The quark-gluon plasma (QGP) phase refers to matter where quarks and gluons are believed to be deconfined and it probably takes place at temperatures of the order of 150 to 170 MeV. In large colliders around the world (RHIC/BNL, ALICE/CERN, GSI, etc), physicists are trying to convert hadronic matter at these order of temperatures into QGP by looking at non-central heavy ion collisions. Possible experiments towards this search are Au-Au collisions at RHIC/BNL and Pb-Pb collisions at SPS/CERN, where the hadron abundances and particle ratios are used in order to determine the temperature and baryonic chemical potential of the possibly present hadronic matter-QGP phase transition. The magnetic fields involved in heavy-ion collisions, although time dependent and short-lived, can reach intensities higher than the ones considered in magnetars, around 1.7 x 10¹⁹ to 10²⁰ Gauss. In fact, the densities related to the chemical potentials obtained within the relativistic models framework developed in previous works are very low (of the order of 10^-3 fm^-3). At these densities the nuclear interactions are indeed very small and this fact made us consider the possibility of free Fermi and Boson gases under the influence of strong magnetic fields. We investigate the effects of magnetic fields of the order of 10¹⁸, 10¹⁹ and 10²⁰ G through a χ² fit to some data sets of the STAR experiment. Our results shown that a field of the order of 10¹⁹ G can produce a much better fit to the experimental data than the calculations without magnetic fields. (author)

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[en] In the present work we study the hadron-quark phase transition by investigating the binodal surface and extending it to finite temperature in order to mimic the QCD (Quantum chromodynamics) phase diagram. In order to obtain these conditions we use different models for the two possible phases, namely the quark and hadron phases. The phase separation boundary (binodal) is determined by the Gibbs criteria for phase equilibrium. The boundaries of the mixed phase and the related critical points for symmetric and asymmetric matter are obtained. Isospin effects appear to be rather significant.

[en] Relativistic nuclear models have been widely used in describing infinite nuclear matter and finite nuclei properties. With the help of the Thomas Fermi approximation, we have investigated droplet formation in the liquid-gas phase transition in cold and warm asymmetric nuclear matters using the non-linear Walecka model. We have shown that the optimal nuclear size of a droplet in a neutron gas is determined by a delicate balance between nuclear Coulomb and surface energies. On the other hand, the production of several intermediate mass fragments in a short time scale during heavy ion collisions is known as nuclear multifragmentation. In these experiments, the spectator matter has been used to investigate a possible liquid-gas phase transition. The caloric curve, which is given by the excitation energy per nucleon in terms of the thermodynamic temperature is an important quantity to be investigated in the search for a signal of a phase transition. In the present work we obtain the excitation energies of arising droplets in a vapor system, up to T = 6.5 MeV. The droplets are described in terms of a non-linear Walecka-type model with the NL1 parameterization, within the Thomas-Fermi approximation. We conclude that the excitation energies of droplets either corresponding to ¹⁵⁰ Sm or ¹⁶⁶ Sm, are consistent with the caloric curve in the Fermi gas approximation with a level density parameter A/13. This result agrees with experimental data obtained in heavy-ion collisions at intermediate energies. We have shown that the caloric curve is sensitive to the proton fraction and the inclusion of the Coulomb interaction is important. (author)