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Sidney S. Avancini

Publications and source records attributed to Sidney S. Avancini.

30 records · Page 2Linked to original sources

Neutral meson properties in hot and magnetized quark matter: a new magnetic field independent regularization scheme applied to NJL-type model

A magnetic field independent regularization scheme (zMFIR) based on the Hurwitz-Riemann zeta function is introduced. The new technique is applied to the regularization of the mean-field thermodynamic potential and mass gap equation within the SU(2) Nambu-Jona-Lasinio model in a hot and magnetized medium. The equivalence of the new and the standard MFIR scheme is demonstrated. The neutral meson pole mass is calculated in a hot and magnetized medium and the advantages of using the new regularization scheme are shown.

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NJL-type models in the presence of intense magnetic fields: the role of the regularization prescription

We study the regularization dependence of the Nambu-Jona--Lasinio model (NJL) predictions for some properties of magnetized quark matter at zero temperature (and baryonic density) in the mean field approximation. The model parameter dependence for each regularization procedure is also analyzed in detail. We calculate the average and difference of the quark condensates using different regularization methods and compare with recent lattice results. In this context, the reliability of the different regularization procedures is discussed.

hep-ph↗

Schwinger mechanism in the SU(3) Nambu--Jona-Lasinio model with an electric field

In this work we study the electrized quark matter under finite temperature and density conditions in the context of the SU(2) and SU(3) Nambu--Jona-Lasinio models. To this end, we evaluate the effective quark masses and the Schwinger quark-antiquark pair production rate. For the SU(3) NJL model we incorporate in the Lagrangian the 't Hooft determinant and we present a set of analytical expressions more convenient for numerical evaluations. We predict a decrease of the pseudocritical electric field with the increase of the temperature for both models and a more prominent production rate for the SU(3) model when compared to the SU(2).

hep-ph↗

Anisotropy in the equation of state of strongly magnetized quark matter within the Nambu--Jona-Lasinio Model

In this article, we calculate the magnetization and other thermodynamical quantities for strongly magnetized quark matter within the Nambu-Jona-Lasinio model at zero temperature. We assume two scenarios, chemically equilibrated charge neutral matter present in the interior of compact stars and zero-strangeness isospin-symmetric matter created in nuclear experiments. We show that the magnetization oscillates with density but in a much more smooth form than what was previously shown in the literature. As a consequence, we do not see the unphysical behavior in the pressure in the direction perpendicular to the magnetic field that was previously found. Finally, we also analyze the effects of a vector interaction on our results.

hep-ph↗

Light Clusters and Pasta Phases in Warm and Dense Nuclear Matter

The pasta phases are calculated for warm stellar matter in a framework of relativistic mean-field models, including the possibility of light cluster formation. Results from three different semiclassical approaches are compared with a quantum statistical calculation. Light clusters are considered as point-like particles, and their abundances are determined from the minimization of the free energy. The couplings of the light-clusters to mesons are determined from experimental chemical equilibrium constants and many-body quantum statistical calculations. The effect of these light clusters on the chemical potentials is also discussed. It is shown that including heavy clusters, light clusters are present until larger nucleonic densities, although with smaller mass fractions.

nucl-th↗

$π_0$ pole mass calculation in a strong magnetic field and lattice constraints

The $π_0$ neutral meson pole mass is calculated in a strongly magnetized medium using the SU(2) Nambu-Jona-Lasinio model within the random phase approximation (RPA) at zero temperature and zero baryonic density. We employ a magnetic field dependent coupling, $G(eB)$, fitted to reproduce lattice QCD results for the quark condensates. Divergent quantities are handled with a magnetic field independent regularization scheme in order to avoid unphysical oscillations. A comparison between the running and the fixed couplings reveals that the former produces results much closer to the predictions from recent lattice calculations. In particular, we find that the $π_0$ meson mass systematically decreases when the magnetic field increases while the scalar mass remains almost constant. We also investigate how the magnetic background influences other mesonic properties such as $f_{π_0}$ and $g_{π_0 q q}$.

hep-ph↗

Properties of magnetized neutral mesons within a full RPA evaluation

We consider the two flavor Nambu--Jona-Lasinio model within the RPA framework to evaluate the masses of the $σ$ and $π^0$ mesons and the $π^0$ decay constant in the presence of a magnetic field at vanishing temperatures and baryonic densities. The present work extends other RPA applications by fully considering the external momenta, which enter the integrals representing the magnetized polarization tensor, so that more accurate results can be obtained in the evaluation of physical quantities containing pionic contributions. As we show, this technical improvement generates results which agree well with those produced by lattice simulations and chiral perturbation theory. Our method may also prove to be useful in future evaluations of quantities such as the shear viscosity and the equation of state of magnetized quark matter with mesonic contributions.

hep-ph↗

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.

nucl-th↗

Imprint of the symmetry energy on the inner crust and strangeness content of neutron stars

In this work we study the effect of the symmetry energy on several properties of neutron stars. First, we discuss its effect on the density, proton fraction and pressure of the neutron star crust-core transition. We show that whereas the first two quantities present a clear correlation with the slope parameter $L$ of the symmetry energy, no satisfactory correlation is seen between the transition pressure and $L$. However, a linear combination of the slope and curvature parameters at $ρ=0.1$ fm$^{-3}$ is well correlated with the transition pressure. In the second part we analyze the effect of the symmetry energy on the pasta phase. It is shown that the size of the pasta clusters, number of nucleons and the cluster proton fraction depend on the density dependence of the symmetry energy: a small $L$ gives rise to larger clusters. The influence of the equation of state at subsaturation densities on the extension of the inner crust of the neutron star is also discussed. Finally, the effect of the effect of the density dependence of the symmetry energy on the strangeness content of neutron stars is studied in the last part of the work. It is found that charged (neutral) hyperons appear at smaller (larger) densities for smaller values of the slope parameter $L$. A linear correlation between the radius and the strangeness content of a star with a fixed mass is also found.

nucl-th↗

The Inner Crust and its Structure

In this chapter we discuss some possible physical pictures that describe the constitution of the inner crust of compact objects. Different relativistic models both with constant couplings and density dependent ones are used. We calculate the liquid-gas phase transition in asymmetric nuclear matter from the thermodynamic and dynamic instabilities. The equations of state used to describe the crust are related to the crust-core transition properties. Cold and warm pasta phases with and without alpha particles are constructed. The influence of the pasta phase and its internal structure on the diffusion coefficients associated with Boltzman transport equations used to simulate the evolution of protoneutron stars are shown. Finally, the possible existence of bare quark stars and the effects of strong magnetic fields on quark matter are considered. Open questions are pointed out.

nucl-th↗

The neutron star inner crust and symmetry energy

The cell structure of clusters in the inner crust of a cold β-equilibrium neutron star is studied within a Thomas Fermi approach and compared with other approaches which include shell effects. Relativistic nuclear models are considered. We conclude that the symmetry energy slope L may have quite dramatic effects on the cell structure if it is very large or small. Rod-like and slab-like pasta clusters have been obtained in all models except one with a large slope L.

nucl-th↗

The QCD Critical End Point Under Strong Magnetic Fields

We use the three-flavor Nambu--Jona-Lasinio model, which includes strangeness and quark physical masses in the mean field approximation, to investigate the influence of strong magnetic fields on the QCD phase diagram covering the whole $T-μ$ plane. It is found that the size of the first order transition line increases as the field strength increases so that a larger coexistence region for hadronic and quark matter should be expected for strong magnetic fields. The location of the critical end point is also affected by the presence of magnetic fields which invariably increase the temperature value at which the first order line terminates. On the other hand, the critical end point chemical potential value displays a subtle oscillation around the B=0 value for magnetic fields within the $10^{17}-10^{20} \, {\rm G}$ range. These findings may have non trivial consequences for the physics of magnetars and heavy ion collisions.

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