arXiv subjects

Constança Providência

Publications and source records attributed to Constança Providência.

At least 127 records · Page 7Linked to original sources

arXiv2016

Neutron stars: from the inner crust to the core with the (Extended) Nambu-Jona-Lasinio model

Nucleonic matter is described within a su(2) extended Nambu-Jona-Lasinio model. Several parametrizations with different nuclear matter saturation properties are proposed. At subsaturation, nuclear pasta phases are calculated within two methods: the coexistence-phases approximation and the compressible liquid drop model, with the surface tension coefficient determined using a geometrical approach at zero temperature. An unified equation of state of stellar matter for the inner crust, with the nuclear pasta phases, and the core is calculated. The mass and radius of neutron stars within this framework are obtained for several families of hadronic and hybrid stars. The quark phase of hybrid stars is described within the su(3) NJL model including a vector term. Stellar macroscopic properties are in accordance with some of the recent results in the literature.

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arXiv2016

The Vlasov formalism for extended relativistic mean field models: the crust-core transition and the stellar matter equation of state

The Vlasov formalism is extended to relativistic mean-field hadron models with non-linear terms up to fourth order and applied to the calculation of the crust-core transition density. The effect of the nonlinear $ωρ$ and $σρ$ coupling terms on the crust-core transition density and pressure, and on the macroscopic properties of some families of hadronic stars is investigated. For that purpose, six families of relativistic mean field models are considered. Within each family, the members differ in the symmetry energy behavior. For all the models, the dynamical spinodals are calculated, and the crust-core transition density and pressure, and the neutron star mass-radius relations are obtained. The effect on the star radius of the inclusion of a pasta calculation in the inner crust is discussed. The set of six models that best satisfy terrestrial and observational constraints predicts a radius of 13.6$\pm$0.3 km and a crust thickness of $1.36\pm 0.06$km for a 1.4 $M_\odot$ star.

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arXiv2015

The QCD phase diagram in the presence of an external magnetic field: the role of the inverse magnetic catalysis

The effect of an external magnetic field in QCD phase diagram, namely, in the the location of the critical end point (CEP) is investigated. Using the 2+1 flavor Nambu--Jona-Lasinio model with Polyakov loop, it is shown that when an external magnetic field is applied its effect on the CEP depends on the strength of the coupling. If the coupling depends on the magnetic field, allowing for inverse magnetic catalysis, the CEP moves to lower chemical potentials eventually disappearing, and the chiral restoration phase transition is always of first order.

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arXiv2015

Influence of the inverse magnetic catalysis and the vector interaction in the location of the critical end point

The effect of a strong magnetic field on the location of the critical end point (CEP) in the QCD phase diagram is discussed under different scenarios. In particular, we consider the contribution of the vector interaction and take into account the inverse magnetic catalysis obtained in lattice QCD calculations at zero chemical potential. The discussion is realized within the (2+1) Polyakov--Nambu--Jona-Lasinio model. It is shown that the vector interaction and the magnetic field have opposite competing effects, and that the winning effect depends strongly on the intensity of the magnetic field. The inverse magnetic catalysis at zero chemical potential has two distinct effects for magnetic fields above $\gtrsim 0.3$ GeV$^2$: it shifts the CEP to lower chemical potentials, hinders the increase of the CEP temperature and prevents a too large increase of the baryonic density at the CEP. For fields $eB<0.1$ GeV$^2$ the competing effects between the vector contribution and the magnetic field can move the CEP to regions of temperature and density in the phase diagram that could be more easily accessible to experiments.

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arXiv2015

Core-collapse supernova matter: light clusters, pasta phase and phase transitions

The pasta phase in core-collapse supernova matter (finite temperatures and fixed proton fractions) is studied within relativistic mean field models. Two different calculations are used for comparison, the Thomas-Fermi (TF) and the Coexisting Phases (CP) approximations. The effects of including light clusters in nuclear matter and the densities at which the transitions between pasta configurations and to uniform matter occur are also investigated. Finally, a comparison with a finite temperature Skyrme-Hartree-Fock calculation is drawn.

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arXiv2015

Effect of the symmetry energy and hyperon interaction on neutron stars

The joint effect of the density dependence of the symmetry energy and strangeness content on the structure of cold neutron stars is studied within the framework of a relativistic mean field theory. It is shown that 2$M_\odot$ are obtained for repulsive $YY$ interaction and preferably for a small or a large slope $L$. An attractive $Σ$ potential in nuclear matter will favor the appearance of strangeness in stars with a mass as small as $\sim 1 M_\odot$, if, however it is repulsive only stars with a mass $\gtrsim 1.4 M_\odot$ will contain strangeness. The joint effect of reducing the symmetry energy slope and including hyperons is to farther reduce the radius. Neutron star maximum mass evolve non-monotonically with the symmetry energy slope, and the smallest masses are obtained for values $L\sim 80$ MeV. Other neutron star variables evolve nonlinearly with the slope of the symmetry energy and depend on the hyperon-nucleon and hyperon-hyperon couplings. The radius of a neutron star is linearly correlated with the neutron star total strangeness fraction and the slope is independent of the slope of the symmetry energy and the mass of the star.

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arXiv2014

Inverse magnetic catalysis in the Polyakov-Nambu-Jona-Lasinio and entangled Polyakov-Nambu-Jona-Lasinio models

We investigate the QCD phase diagram at zero chemical potential and finite temperature in the presence of an external magnetic field within the three flavor Polyakov-Nambu-Jona-Lasinio and entangled Polyakov-Nambu-Jona-Lasinio models looking for the inverse magnetic catalysis. Two scenarios for a scalar coupling parameter dependent on the magnetic field intensity are considered. These dependencies of the coupling allow to reproduce qualitatively lattice QCD results for the quark condensates and for the Polyakov loop: due to the magnetic field the quark condensates are enhanced at low and high temperatures and suppressed for temperatures close to the transition temperatures while the Polyakov loop increases with the increasing of the magnetic field.

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arXiv2014

Quark matter subject to strong magnetic fields: phase diagram and applications

In the present work we are interested in understanding various properties of quark matter subject to strong magnetic fields described by the Nambu-Jona-Lasinio model with Polyakov loop. We start by analysing the differences arising from two different vector interactions in the Lagrangian densities, at zero temperature, and apply the results to stellar matter. We then investigate the position of the critical end point for different chemical potential and density scenarios.

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arXiv2014

The QCD critical end point driven by an external magnetic field in asymmetric quark matter

The effect of the isospin/charge asymmetry and an external magnetic field in the location of the critical end point (CEP) in the QCD phase diagram is investigated. By using the 2+1 flavor Nambu--Jona-Lasinio model with Polyakov loop (PNJL), it is shown that the isospin asymmetry shifts the CEP to larger baryonic chemical potentials and smaller temperatures, and in the presence of a large enough isospin asymmetry the CEP disappears. Nevertheless, a sufficiently high external magnetic field can drive the system into a first order phase transition again.

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arXiv2014

Strange quark chiral phase transition in hot 2+1-flavor magnetized quark matter

Using the Polyakov--Nambu--Jona-Lasinio model the strange quark chiral phase transition and the effect of its current mass on a hot magnetized three flavor quark matter at zero chemical potential is investigated. The impact of the 't Hooft mixing term on the restoration of the chiral symmetry on the light and strange sectors is studied and the critical temperature dependence on the magnetic field strength of the chiral strange transition is analyzed. It is shown that the s quark is much less sensitive to the magnetic field than the light quarks. Due to the 't Hooft term, it has a strong influence on the light quarks at all temperatures for small magnetic fields and for temperatures close to the transition temperature at zero magnetic field and above for strong magnetic fields. In particular, the large mass of the s quark makes the chiral transition of the light sector smoother and shifted to larger temperatures. A scalar coupling that weakens when the magnetic field increases will originate an inverse magnetic catalysis also in the s quark and smoothen the signature of the crossover on thermodynamical quantities such as the sound velocities or the specific heat.

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arXiv2014

Equation of state and thickness of the inner crust of neutron stars

The cell structure of $β$-stable clusters in the inner crust of cold and warm neutron stars is studied within the Thomas-Fermi approach using relativistic mean field nuclear models. The relative size of the inner crust and the pasta phase of neutron stars is calculated, and the effect of the symmetry energy slope parameter, $L$, on the profile of the neutron star crust is discussed. It is shown that while the size of the total crust is mainly determined by the incompressibility modulus, the relative size of the inner crust depends on $L$. It is found that the inner crust represents a larger fraction of the total crust for smaller values of $L$. Finally, it is shown that at finite temperature the pasta phase in $β$-equilibrium matter essentially melts above $5-6$ MeV, and that the onset density of the rodlike and slablike structures does not depend on the temperature.

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arXiv2014

Deconfinement, chiral symmetry restoration and thermodynamics of (2+1)--flavor hot QCD matter in an external magnetic field

The entanglement extended Polyakov--Nambu--Jona-Lasinio model at zero chemical potential in the presence of an external magnetic field is studied. The effect of the entanglement parametrization is analyzed, in particular, on the pseudocritical transition temperatures and on the thermodynamical properties of the model. The model predicts that the coincidence or not of both chiral and deconfinement transition temperatures, in the presence of an external magnetic field, depends on the entanglement parametrization chosen.

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arXiv2014

Phase transition and critical end point driven by an external magnetic field in asymmetric quark matter

The location of the critical end point (CEP) in the QCD phase diagram is determined under different scenarios. The effect of strangeness, isospin/charge asymmetry and an external magnetic field is investigated. The discussion is performed within the 2+1 flavor Nambu--Jona-Lasinio model with Polyakov loop. It is shown that isospin asymmetry shifts the CEP to larger baryonic chemical potentials and smaller temperatures. At large asymmetries the CEP disappears. However, a strong enough magnetic field drives the system into a first order phase transition.

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arXiv2013

Deconfinement and chiral restoration within the SU(3) Polyakov--Nambu--Jona-Lasinio and entangled Polyakov--Nambu--Jona-Lasinio models in an external magnetic field

The behavior of the quark condensates at zero chemical potential and finite temperature subject to an external magnetic field is studied within the three flavor Nambu--Jona-Lasinio model with Polyakov loop (PNJL) and its extension, the so-called entangled PNJL model (EPNJL). A comparison with recent lattice QCD data is performed and it is shown that at $T=0$ MeV the light quark condensates are in quantitative agreement. At finite temperature, although there is an overall reasonable agreement with several lattice results, it is shown that in the lattice calculations the effect due to the electric charge quark difference is stronger and the restoration of the $u$ quark chiral symmetry starts at lower temperatures. When considering the EPNJL model with a Polyakov loop scale parameter that depends on the magnetic field, it is possible to obtain an earlier rise of the Polyakov loop with the increase of the magnetic field and due to the entanglement, the inverse magnetic catalysis is found as in the lattice QCD calculations.

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arXiv2013

Effects of the symmetry energy on the kaon condensates in the QMC Model

In this work we investigate protoneutron star properties within a modified version of the quark coupling model (QMC) that incorporates a omega-rho interaction plus kaon condensed matter at finite temperature. Fixed entropy and trapped neutrinos are taken into account. Our results are compared with the ones obtained with the GM1 parametrization of the non-linear Walecka model for similar values of the symmetry energy slope. Contrary to GM1, within the QMC the formation of low mass black-holes during cooling are not probable. It is shown that the evolution of the protoneutron star may include the melting of the kaon condensate driven by the neutrino diffusion, followed by the formation of a second condensate after cooling. The signature of this complex proccess could be a neutrino signal followed by a gamma ray burst. We have seen that both models can, in general, describe very massive stars.

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arXiv2013

Formation of hybrid stars from metastable hadronic stars

We study the consequences of quark matter nucleation in cold hadronic matter employing three relativistic-mean-field (RMF) models to describe the hadronic phase and the Nambu-Jona-Lasinio (NJL) model for the quark one. We explore the effect of a vector interaction in the NJL Lagrangian and of a phenomenological bag constant on neutron stars metastability. We delineate the region of parameters of the quark phase that allow for the formation of stable hybrid stars with mass compatible with the almost $2 \ M_\odot$ pulsars PSR J1614-2230 ($1.97 \pm 0.04 M_\odot$) and PSR J0348+0432 ($2.01 \pm 0.04 M_\odot$). It is shown, however, that not all hybrid star configurations with $\sim 2 \,M_\odot$ are populated after nucleation.

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arXiv2013

Tensor force effects and high-momentum components in the nuclear symmetry energy

We analyze microscopic many-body calculations of the nuclear symmetry energy and its density dependence. The calculations are performed in the framework of the Brueckner-Hartree-Fock and the Self-Consistent Green's Functions methods. Within Brueckner-Hartree-Fock, the Hellmann-Feynman theorem gives access to the kinetic energy contribution as well as the contributions of the different components of the nucleon-nucleon interaction. The tensor component gives the largest contribution to the symmetry energy. The decomposition of the symmetry energy in a kinetic part and a potential energy part provides physical insight on the correlated nature of the system, indicating that neutron matter is less correlated than symmetric nuclear matter. Within the Self-Consistent Green's Function approach, we compute the momentum distributions and we identify the effects of the high momentum components in the symmetry energy. The results are obtained for the realistic interaction Argonne V18 potential, supplemented by the Urbana IX three-body force in the Brueckner-Hartree-Fock calculations.

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arXiv2013

Effect of strong magnetic fields on the pasta phase structure

The effect of strong magnetic fields on the properties of the pasta structures is calculated within a Thomas Fermi approach using relativistic mean field models to modulate stellar matter. It is shown how quantities such as the size of the clusters and Wigner-Seitz cells, the surface tension and the transition between configurations are affected. It is expected that these effects may give rise to large stresses in the pasta phase if the local magnetic field suffers fluctuations.

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