S. B. Duarte

Massive Compact Stars as Quark Stars

High massive compact stars have been reported recently in the literature, providing strong constraints on the properties of the ultradense matter beyond the saturation nuclear density. In view of these results, the calculations of quark star or hybrid star equilibrium structure must be compatible with the provided observational data. But, since the used equations of state describing quark matter are in general too soft, in comparison with the equation of states used to describe the hadronic or nuclear matter, the calculated quark star models presented in the literature are in general not suitable to explain the stability of high compact massive objects.

DELTA MATTER FORMATION IN DENSE ASYMMETRIC NUCLEAR MEDIUM

In the context of a relativistic mean field theory the delta-resonance matter formation in a highly compressed nuclear medium is investigated. For a given set of nucleon–meson coupling constants, the delta-resonance formation is studied by changing the delta-meson coupling constants. The effect on the equation of state and on the delta-resonance population with respect to changes in the delta-resonance coupling constants values is discussed for very asymmetric and quasi-symmetric nuclear matter, as an extension of works restricted to the symmetric nuclear matter treatment.5,6

EFFECTS OF Δ-BARYON INTERACTION STRENGTH ON NEUTRON STARS PROPERTIES

We investigate the effect of Δ-resonance interaction strength on the equation of state of asymmetric hadronic matter and neutron stars structure. We discuss Δ-matter formation at high densities in the context of a relativistic mean field theory. We show that the attractive nature of the Δ-baryon interaction can induce a phase transition accompanying Δ-matter formation, at values of densities presumably existing in central regions of neutron stars. The possibility of a rich Δ-resonance neutron star is presented using the proposed equation of state.

Perfect transfer of quantum states in a network of harmonic oscillators

This work presents an exactly soluble scheme to address the problem of optimal transfer of quantum states through a set of s harmonic oscillators composing a network with connected ends as a closed quantum circuit. For this purpose we start from a general quadratic Hamiltonian form. The relationship between the parameters of the Hamiltonian, the network size, and the time interval required for such transfer are explicitly shown. Particular physical realizations of this Hamiltonian, transfer of entangled states, including transfer of states at the expense of a quantum entanglement, are also considered.

Computational procedure to determine quantum state evolution in Fock space

A new algorithm to solve the quantum state evolution of a system described by a general quadratic Hamiltonian form in creation and the annihilation operators of Fock space is presented. The nonlinear equation for the dynamic operators are obtained in the matrix representation, and by a recursive relation the time evolution operator in the Fock basis is constructed. The method permits to obtain the evolution of entangled quantum states of interacting subsystems when the Hamiltonian of the whole system is in the above mentioned form. Numerical solution with the method is sufficiently accurate to safely analyze the important question of quantum state transfer between the interacting subsystems. A qubits transfer is discussed as an illustrative example when the method is applied to a system described by a particular quadratic Hamiltonian form.

Delta Resonance Coupling with Walecka’s Mesons: Implications to Stellar Matter EoS

In this work we have obtained the equation of state to the highly asymmetric dense stellar matter, using the nonlinear Walecka model in the mean field approximation. We discussed the implication of changes in coupling constant of the delta baryonic resonance on the observable of the neutron star. A detailed analysis of the equation of state and of the baryonic effective mass in respect to changes in the delta coupling constants is carried out. We focus attention on a new aspect observed for pressure when varying the baryonic density of the medium; a first order phase transition like a liquid-gas phase transition was observed for an acceptable range of delta coupled constant values. We have explored the implication of this aspect for the neutron star structure and their maximum masses.

Shock wave produced by hadron-quark phase transition in neutron star

In this work we present a schematic description of the detonation wave in hadronic matter inside a neutron star core. We have used a simplified two shells model where the inner shell medium is initially composed of a small lump of strange quark matter surrounded by a large outer shell composed of hadronic matter. We have utilized an equation of state (EOS) based on Relativistic Mean Field Theory with the parameter set NL3 to describe the nuclear and subnuclear phases. We use the MIT bag model to describe the strange quark matter. The hadron-quark phase transition actually induces highly non equilibrium modes, which may become a detonation process (faster) or a burning process (slower). The main purpose of the work is to study the formation of a remnant quark star and the possibility of mass ejection caused by the hadron-quark phase transition. We have found that the total amount of ejected mass is dependant of the bag constant utilized in the strange matter description.

New thermal model with distinct freeze-out temperatures for baryons and mesons

A significant amount of experimental data for particle production in high-energy heavy ion collisions (10 - 200 GeV/A at center of mass) has been accumulated during last years. Many different theoretical attempts have tried to describe these data using thermal models in the approximation of global thermal equilibrium considering only one freeze-out temperature. However the thermal models often are not able to describe adequately the whole multiplicities of hadrons. For instance, the abundance of strange particles is overestimate and the pion yields are underestimated. In this work is presented a thermal hadronic model with two different temperatures in order to describe the baryonic and mesonic chemical freeze-out in ultra-relativistic heavy ion collisions. The model is used to fit the particle population ratios of the hadrons produced in the reaction. The proposal is not merely to incorporate one additional degree of freedom in the adjustment procedure of data, but to present and alternative scenario for the freeze out stage in the collisional proces s. This new reformulated version of thermal model was applied to a set of data, offering a rather good improvement in the fitting of the calculated particle ratios to the data. The results suggest that the introduced model makes the thermal approach more robust to handle with a larger number of colliding systems and a more comprehensive set of reaction observables.

Gravitational Wave Radiated by a Collapsing Ellipsoid

In this work we present a simplified effective description of the final state of the gravitational collapse of a uniformly rotating protoneutron star, approximated by a compressible homogeneous triaxial ellipsoid. The generation of gravitational waves is treated within the weak field limit. The method can be applied to estimate the intensity of the radiated gravitational waves during the core collapse.

Proto-Neutron Stars with Delta-Resonances using the Zimanyi-Moszkowski Model

In this work we have obtained the equation of state to be used in the study of the structure of protoneutron stars. To this end, we adopted the model of Zimanyi-Moszkowski (ZM) in the mean field approximation. We analyse the effects of the trapped neutrinos on the equation of state during the initial formation of a neutron star. We determine the Mass×Radius diagram of proto-neutron stars including the delta resonances in the baryonic sector and trapped neutrinos. The result is compared with that for the formed neutron star after the cooling phase, without trapped neutrino in the stelar medium.