arXiv subjects

C. Providência

Publications and source records attributed to C. Providência.

31 records · Page 2Linked to original sources

arXiv2011

Warm and dense stellar matter under strong magnetic fields

We investigate the effects of strong magnetic fields on the equation of state of warm stellar matter as it may occur in a protoneutron star. Both neutrino free and neutrino trapped matter at a fixed entropy per baryon are analyzed. A relativistic mean field nuclear model, including the possibility of hyperon formation, is considered. A density dependent magnetic field with the magnitude $10^{15}$ G at the surface and not more than $3\times 10^{18}$ G at the center is considered. The magnetic field gives rise to a neutrino suppression, mainly at low densities, in matter with trapped neutrinos. It is shown that an hybrid protoneutron star will not evolve to a low mass blackhole if the magnetic field is strong enough and the magnetic field does not decay. However, the decay of the magnetic field after cooling may give rise to the formation of a low mass blackhole.

nucl-th↗

arXiv2010

$α$ particles and the pasta phase

The effects of the $α$ particles in nuclear matter at low densities are investigated within three different parametrizations of relativistic models at finite temperature. Both homogeneous and inhomogeneous matter (pasta phase) are described for neutral nuclear matter with fixed proton fractions and stellar matter subject to $β$-equilibrium and trapped neutrinos. In homogeneous matter, $α$ particles are only present at densities below 0.02 fm$^{-3}$ and their presence decreases with the increase of the temperature and, for a fixed temperature, the $α$ particle fraction decreases for smaller proton fractions. A repulsive interaction is important to mimic the dissolution of the clusters in homogeneous matter. The effects of the $α$ particles on the pasta structure is very small except close to the critical temperatures and / or proton fractions when it may still predict a pasta phase while no pasta phase would occur in the absence of light clusters. It is shown that for densities above 0.01 fm$^{-3}$ the $α$ particle fraction in the pasta phase is much larger than the $α$ particle fraction in homogeneous matter.

nucl-th↗

arXiv2010

Compact stars with a quark core within NJL model

An ultraviolet cutoff dependent on the chemical potential as proposed by Casalbuoni {\it et al} is used in the su(3) Nambu-Jona-Lasinio model. The model is applied to the description of stellar quark matter and compact stars. It is shown that with a new cutoff parametrization it is possible to obtain stable hybrid stars with a quark core. A larger cutoff at finite densities leads to a partial chiral symmetry restoration of quark $s$ at lower densities. A direct consequence is the onset of the $s$ quark in stellar matter at lower densities and a softening of the equation of state.

nucl-th↗

arXiv2010

Quarks stars in SU(2) Nambu-Jona-Lasinio model with vector coupling

In this work we study the Nambu-Jona-Lasinio model in the SU (2) version with repulsive vector coupling and apply it to quark stellar matter. We discuss the influence of the vector interaction on the equation of state (EoS) and study quark stars that are composed of pure quark matter with two flavors. We show that, increasing the vector coupling, we obtain more massive stars with larger radii for the same central energy density.

nucl-th↗

arXiv2009

Particle Production within the Quark Meson Coupling Model

Quark meson coupling (QMC) models can be successfully applied to the description of compact star properties in nuclear astrophysics as well as to nuclear matter. In the regime of hot hadronic matter very few calculations exist using the QMC model, in particular when applied to particle yields in heavy ion collisions. In the present work, we identify the free energy of the bag with the effective mass of the baryons and we calculate the particle production yields on a Au+Au collision at RHIC with the QMC model and compare them with results obtained previously with other relativistic models. A smaller temperature for the fireball, T=132 MeV, is obtained due to the smaller effective baryon masses predicted by QMC. QMC was also applied to the description of particle yields at SPS in Pb+Pb collisions.

nucl-th↗

arXiv2009

Determination of the neutron star mass-radii relation using narrow-band gravitational wave detector

The direct detection of gravitational waves will provide valuable astrophysical information about many celestial objects. The most promising sources of gravitational waves are neutron stars and black holes. These objects emit waves in a very wide spectrum of frequencies determined by their quasi-normal modes oscillations. In this work we are concerned with the information we can extract from f and p$_I$-modes when a candidate leaves its signature in the resonant mass detectors ALLEGRO, EXPLORER, NAUTILUS, MiniGrail and SCHENBERG. Using the empirical equations, that relate the gravitational wave frequency and damping time with the mass and radii of the source, we have calculated the radii of the stars for a given interval of masses $M$ in the range of frequencies that include the bandwidth of all resonant mass detectors. With these values we obtain diagrams of mass-radii for different frequencies that allowed to determine the better candidates to future detection taking in account the compactness of the source. Finally, to determine which are the models of compact stars that emit gravitational waves in the frequency band of the mass resonant detectors, we compare the mass-radii diagrams obtained by different neutron stars sequences from several relativistic hadronic equations of state (GM1, GM3, TM1, NL3) and quark matter equations of state (NJL, MTI bag model). We verify that quark stars obtained from MIT bag model with bag constant equal to 170 MeV and quark of matter in color-superconductivity phase are the best candidates for mass resonant detectors.

gr-qc↗

arXiv2007

Dynamical instabilities in density-dependent hadronic relativistic models

Unstable modes in asymmetric nuclear matter (ANM) at subsaturation densities are studied in the framework of relativistic mean-field density-dependent hadron models. The size of the instabilities that drive the system are calculated and a comparison with results obtained within the non-linear Walecka model is presented. The distillation and anti-distillation effects are discussed.

nucl-th↗

arXiv2007

Density dependent hadronic models and the relation between neutron stars and neutron skin thickness

In the present work we investigate the main differences in the lead neutron skin thickness, binding energy, surface energy and density profiles obtained with two different density dependent relativistic hadronic models, within the Thomas-Fermi approximation. We show that the asymmetry parameter for low momentum transfer polarized electron scattering is not sensitive to the model parametrization differences.

nucl-th↗

arXiv2005

Pentaquarks in the medium in the quark-meson coupling model

We calculate the properties of the pentaquarks $Θ^+$ and $Ξ^{--,0}$ in symmetric nuclear matter using the quark meson coupling model (QMC). The stability of the $Θ^+$ in the medium with respect to the channel $Θ^+\to NK^+$ is discussed.

nucl-th↗

arXiv2004

Aspects of short range correlations in a relativistic model

In the present work short range correlations are introduced for the first time in a relativistic approach to the equation of state of the infinite nuclear matter in the framework of the Hartree-Fock approximation using an effective Hamiltonian derived from the $σ-ω$ Walecka model. The unitary correlation method is used to introduce short range correlations. The effect of the correlations in the ground state properties of the nuclear matter is discussed.

nucl-th↗

arXiv2004

Stellar matter in the Quark-Meson-Coupling Model with neutrino trapping

The properties of hybrid stars formed by hadronic and quark matter in $β$-equilibrium are described by appropriate equations of state (EoS) in the framework of the quark meson coupling (QMC) model. In the present work we include the possibility of trapped neutrinos in the equation of state and obtain the properties of the related hybrid stars. We use the quark meson coupling model for the hadron matter and two possibilities for the quark matter phase, namely, the unpaired quark phase and the color-flavor locked phase. The differences are discussed and a comparison with other relativistic EoS is done.

nucl-th↗

arXiv2003

Hybrid stars in the quark-meson coupling model with superconducting quark matter

The phase transition to a deconfined phase is studied and the consequences in the formation of neutron stars are investigated. We use the quark-meson-coupling model for the hadron matter and the MIT Bag model for the quark matter in order to build the appropriate equations of state for the hybrid stars. The properties of the stars are then calculated. The differences between unpaired and color-flavor locked quark matter are discussed.

nucl-th↗

arXiv2003

Warm asymmetric matter in the Quark Meson Coupling Model

In this work we study the warm equation of state of asymmetric nuclear matter in the quark meson coupling model which incorporates explicitly quark degrees of freedom, with quarks coupled to scalar, vector and isovector mesons. Mechanical and chemical instabilities are discussed as a function of density and isospin asymmetry. The binodal section, essential in the study of the liquid-gas phase transition is also constructed and discussed. The main results for the equation of state are compared with two common parametrizations used in the non-linear Walecka model and the differences are outlined.

nucl-th↗