In the present work we calculate the adiabatic index of neutron stars formed by hadronic or quarkionic matter, under two possible conditions, with and without trapped neutrinos, and for two values of the entropy per baryon S = 0,2 kB/ baryon. We use the nonlinear Walecka model to describe hadronic stars, and the MIT bag model to describe quark stars. Particle fractions for each case are obtained and the appearance of particles are compared with drops in the adiabatic index, whenever possible.

In the present work we investigate one possible variation on the usual electrically neutral pulsars: the inclusion of electric charge through a naive prescription. We study the effect of electric charge in pulsars assuming that the charge distribution is proportional to the energy density. All calculations were performed for equations of state obtained at zero temperature and also for fixed entropies. We then choose one of the models, the Nambu-Jona-Lasinio model for zero temperature quark stars without the inclusion of leptons, what makes them electrically charged, and compare the results with the previous one.

In order to investigate the instabilities in asymmetric nuclear matter described within relativistic mean field hadron models, we build the spinodals. We have used relativistic models both with constant and density dependent couplings at zero and finite temperatures. We have seen that the main differences in the spinodals occur at finite temperature and large isospin asymmetry close to the boundary of the instability regions.

In the study of two interacting systems within the framework of microscopic theories, the correct treatment of the effective interaction between the fragments has been the most troubling problem, due to the technical difficulties in calculating the exchange terms. In the framework of the Generator Coordinate Method, and through a double projection technique, we obtain this effective interaction between two pairs of nucleons, taking into account the Coulomb exchange plus a nuclear part. Our treatment is useful in the analysis of the role of correlated nucleon pairs in photoabsorption experiments by nuclei.

In order to obtain the properties of compact stellar objects, appropriate equations of state have to be used. In the literature, strange meson fields, namely the scalar meson field sigma*(975) and the vector meson field phi(1020), had to be considered in order to reproduce the observed strongly attractive <FONT FACE=Symbol>LL</FONT> interaction. The introduction of these strange mesons makes the equations of state harder (EOS) due to the repulsive effect of the phi(1020) meson. In this work the inclusion of these mesons in the equation of state and their influence on the properties of the neutron stars are investigated.

Short range correlations are introduced using unitary correlation method in a relativistic approach to the equation of state of the infinite nuclear matter in the framework of the Hartree-Fock approximation. The effect of the correlations in the ground state properties of the nuclear matter is studied.

In this work we study the effects of temperature on the equations of state within a relativistic model, with the inclusion of the baryons of the octet over a wide range of densities. We compare the results of the equation of state, effective mass and strangeness fraction for the TM1, NL3 and GL sets of parameters.

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 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.

The structure of infinite nuclear matter is studied with two of the Zimanyi - Moszkowski (ZM) models in the framework of a relativistic approximation which takes into account Hartree terms and beyond and is compared with the results which come out of the relativistic Hartree - Fock approach in the linear Walecka model. The simple treatment applied to these models can be used in substitution to the more complicated Dirac - Brueckner - Hartree - Fock method to perform future calculations in finite nuclei