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D. P. Menezes

Publications and source records attributed to D. P. Menezes.

At least 19 recordsLinked to original sources

Hybrid Stars Built with Density Dependent Models

Using a density dependent quark model and a relativistic model within the mean-field approximation for hadrons with density dependent meson-baryon couplings, we construct, for the first time, models that describe hybrid neutron stars consisting of nucleons and exotic baryons (hyperons and $Δ$-resonances). We do the study using a Maxwell construction. The quark-hadron phase transition in the stellar matter is determined through; the structure, composition, and properties of the hybrid neutron star matter. The macroscopic properties of the star are determined, and the results for these particular models are found to be compatible with recent observational astrophysical data.

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Evidence of fractal structures in hadrons

This study focuses on the presence of (multi)fractal structures in confined hadronic matter through the momentum distributions of mesons produced in proton-proton collisions between 23 GeV and 63 GeV. The analysis demonstrates that the $q$-exponential behaviour of the particle momentum distributions is consistent with fractal characteristics, exhibiting fractal structures in confined hadronic matter with features similar to those observed in the deconfined quark-gluon plasma (QGP) regime. Furthermore, the systematic analysis of meson production in hadronic collisions at energies below 1 TeV suggests that specific fractal parameters are universal, independently of confinement or deconfinement, while others may be influenced by the quark content of the produced meson. These results pave the way for further research exploring the implications of fractal structures on various physical distributions and offer insights into the nature of the phase transition between confined and deconfined regimes.

hep-th

Phase transitions and latent heat in magnetized matter

Based on the assumption that the QCD phase diagram gives a realistic picture of hadronic and quark matter under different regimes, it is possible to claim that a quark core may be present inside compact objects commonly named hybrid neutron stars or even that a pure strange star may exist. In this work we explore how the phase transition is modified by the presence of strong magnetic fields and how it is impacted by parameters of the quark phase, for which we use the MIT-model with vector interactions. The phase transition is assumed to conserve flavor when hadrons turn into deconfined quarks. The hadronic equation of state is calculated with the NL3$ωρ^\ast$ parametrization of quantum hadrodynamics. We find that the magnetic field slightly reduces the pressure and chemical potential of the phase transition and the latent heat, the latter being very model dependent.

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Exploring the effects of Delta Baryons in magnetars

Strong magnetic fields can modify the microscopic composition of matter with consequences on stellar macroscopic properties. Within this context, we study, for the first time, the possibility of the appearance of spin-3/2 $Δ$ baryons in magnetars. We make use of two different relativistic models for the equation of state of dense matter under the influence of strong magnetic fields considering the effects of Landau levels and the anomalous magnetic moment (AMM) proportional to the spin of all baryons and leptons. In particular, we analyze the effects of the AMM of $Δ$ baryons in dense matter for the first time. {We also obtain global properties corresponding to the EoS models numerically and study the corresponding role of the $Δ$ baryons.} We find that they are favored over hyperons, which causes an increase in isopin asymmetry and a decrease in spin polarization. We also find that, contrary to what generally occurs when new degrees of freedom are introduced, the $Δ$s do not make the EoS significantly softer and magnetars less massive. Finally, the magnetic field distribution inside a given star is not affected by the presence of $Δ$s.

astro-ph.HE

Density dependent quark mass model revisited: Thermodynamic consistency, stability windows and stellar properties

In this work a density dependent quark model is revisited, its thermodynamic consistency checked and the stability window for absolutely stable quark matter obtained. The hypotheses of both pure quark matter with equal quark chemical potentials and stellar matter subject to chemical stability and charge neutrality are investigated. The parameters that appear in the density dependent mass and satisfy the Bodmer-Witten conjecture are then used to compute the masses and radii of strange stars. We show that the obtained values are compatible with the recently observed massive stars.

hep-ph

Consistent Skyrme parametrizations constrained by GW170817

The high-density behavior of the stellar matter composed of nucleons and leptons under $β$~equilibrium and charge neutrality conditions is studied with the Skyrme parametrizations shown to be consistent (CSkP) with the nuclear matter, pure neutron matter, symmetry energy and its derivatives in a set of $11$ constraints [Dutra {\it et al.}, Phys. Rev. C 85, 035201 (2012)]. The predictions of these parametrizations on the tidal deformabilities related to the GW170817 event are also examined. The CSkP that produce massive neutron stars give a range of $11.86~\mbox{km} \leqslant R_{1.4} \leqslant 12.55~\mbox{km}$ for the canonical star radius, in agreement with other theoretical predictions. It is shown that the CSkP are compatible with the region of masses and radii obtained from the analysis of recent data from LIGO and Virgo Collaboration (LVC). A correlation between dimensionless tidal deformability and radius of the canonical star is found, namely, $Λ_{1.4} \approx 3.16\times10^{-6}R_{1.4}^{7.35}$, with results for the CSkP compatible with the recent range of $Λ_{1.4}=190_{-120}^{+390}$ from LVC. An analysis of the $Λ_1\timesΛ_2$ graph shows that all the CSkP are compatible with the recent bounds obtained by LVC. Finally, the universal correlation between the moment of inertia and the deformability of a neutron star, named as the \mbox{$I$-Love} relation, is verified for the CSkP, that are also shown to be consistent with the prediction for the moment of inertia of the \mbox{PSR J0737-3039} primary component pulsar.

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Consistent relativistic mean-field models: critical parameters values

We revisit the study published in [1], related to the behavior of 34 relativistic mean-field models, previously selected because they satisfy bulk nuclear matter properties, here used to compute the critical parameters of the symmetric nuclear matter. We evaluate their critical temperature, pressure, and density and compare with some values encountered in the literature. We also show that these parameters are correlated with the incompressibility calculated at the zero temperature regime.

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Critical parameters of consistent relativistic mean-field models

In the present work, the critical temperature, critical pressure and critical density, known as the critical parameters related to the liquid-gas phase transition are calculated for 34 relativistic mean-field models, which were shown to satisfy nuclear matter constraints in a comprehensive study involving 263 models. The compressibility factor was calculated and all 34 models present values lower than the one obtained with the van der Waals equation of state. The critical temperatures were compared with experimental data and just two classes of models can reach values close to them. A correlation between the critical parameters and the incompressibility was obtained.

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Relativistic Mean-Field Hadronic Models under Nuclear Matter Constraints

Relativistic mean-field (RMF) models have been widely used in the study of many hadronic frameworks because of several important aspects not always present in nonrelativistic models, such as intrinsic Lorentz covariance, automatic inclusion of spin, appropriate saturation mechanism for nuclear matter, causality and, therefore, no problems related to superluminal speed of sound. With the aim of identifying the models which best satisfy well known properties of nuclear matter, we have analyzed $263$ parameterizations of seven different types of RMF models under three different sets of constraints related to symmetric nuclear matter, pure neutron matter, symmetry energy, and its derivatives. One of these (SET1) is formed of the same constraints used in a recent work [M. Dutra et al., Phys. Rev. C 85, 035201 (2012)] in which we analyzed $240$ Skyrme parameterizations. The results pointed to $2$ models consistent with all constraints. By using another set of constraints, namely, SET2a, formed by the updated versions of the previous one, we found $4$ models approved simultaneously. Finally, in the third set, named SET2b, in which the values of the constraints are more restrictive, we found $3$ consistent models. Another interesting feature of our analysis is that the results change dramatically if we do not consider the constraint regarding the volume part of the isospin incompressibility ($K_{τ,\rm v}$). In this case, we have $35$ approved models in SET2a and $30$ in SET2b.

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Effects of the Symmetry Energy and its Slope on Neutron Star Properties

In this work we study the influence of the symmetry energy and its slope on three major properties of neutron stars: the maximum mass, the radii of the canonical 1.4$M_\odot$ and the minimum mass that enables the direct URCA effect. We utilize four parametrizations of the relativistic quantum hadrodynamics and vary the symmetry energy within accepted values. We see that although the maximum mass is almost independent of it, the radius of the canonical $1.4M_\odot$ and the mass that enables the direct URCA effect is strongly correlated with the symmetry energy and its slope. Also, since we expect that the radius grows with the slope, a theoretical limit arises when we increase this quantity above certain values.

astro-ph.HE

Phase structure of cold magnetized quark matter within the SU(3) NJL model

The possible different phases of cold quark matter in the presence of a finite magnetic field and chemical potential are obtained within the SU(3) NJL model for two parameter sets often used in the literature. Although the general pattern is the same in both cases, the number of intermediate phases is parameter dependent. The chiral susceptibilities, as usually defined, are different not only for the s-quark as compared with the two light quarks, but also for the u and d-quarks, yielding non identical crossover lines for the light quark sector.

hep-ph

The influence of strong magnetic fields on proto-quark stars

We analyze different stages of magnetized quark star evolution incorporating baryon number conservation and using an anisotropic energy momentum tensor. The first stages of the evolution are simulated through the inclusion of trapped neutrinos and fixed entropy per particle, while in the last stage the star is taken to be deleptonized and cold. We find that, although strong magnetic fields modify quark star masses, the evolution of isolated stars needs to be constrained by fixed baryon number, which necessarily lowers the possible star masses. Moreover, magnetic field effects, measured by the difference between the parallel and perpendicular pressures, are more pronounced in the beginning of the star evolution, when there is a larger number of charged leptons and up quarks. We also show that having a spatially varying magnetic field allows for larger magnetic fields to be supported.

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Hadronic and hybrid stars subject to density dependent magnetic fields

In this work we present a study of magnetars composed of hadronic and quark matter, under the influence of strong magnetic fields. We present our results for hadronic matter taking into account the effects that the inclusion of anomalous magnetic moment corrections may cause on the equations of state (EOS). Particle abundances are also presented and discussed. Additionally, the case of hybrid stars under the influence of strong magnetic fields is considered. We study the structure of hybrid stars based on the Maxwell condition (without a mixed phase), where the hadron phase is described by the non-linear Walecka model (NLW) and the quark phase by the Nambu-Jona-Lasinio model (NJL). The EOS and the mass-radius relation for each case are calculated and discussed. We show that the recently observed high mass neutron stars can be described by both hadronic and hybrid equations of state subject to strong magnetic fields.

astro-ph.SR

Stability windows for proto-quark stars

We investigate the existence of possible stable strange matter and related stability windows at finite temperature for different models that are generally applied to describe quark stars, namely, the quark-mass density dependent model, the MIT bag model and the Nambu-Jona-Lasinio model. We emphasize that, although the limits for stable strange matter depend on a comparison with the ground state of 56Fe, which is a zero temperature state, the quantity that has to be used in the search for strange matter in proto-quark stars is the free energy and we analyze stability windows up to temperatures of the order of 40 MeV. The effects of strong magnetic fields on stability windows are computed and the resulting mass-radius relations for different stages of the proto-quark star are analyzed.

astro-ph.HE

Stability windows at finite temperature

The assumption underlying the existence of quark stars is based on the Bodmer-Witten conjecture. These authors have claimed that it is possible that the interior of a neutron-like star does not consist primarily of hadrons, but rather of the strange matter (SM). Strange matter is composed of deconfined quarks, including up, down and strange quarks, plus the leptons necessary to ensure charge neutrality and β-equilibrium. This possibility arises because a phase transition from hadronic to quark phase is possible at densities present in the interior of neutron stars. It has been argued that strange matter is the true ground state of all matter. If this is the case, as soon as the core of the star converts to the quark phase, the entire star converts. SM was first considered in calculations obtained within the MIT bag model framework. More sophisticated treatments for SM, based on the quark-mass density dependent model is considered in this work. We discuss next the following models for proto-quark stars: the QMDD model, and the MIT bag model.

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Relativistic Mean-Field Models and Nuclear Matter Constraints

This work presents a preliminary study of 147 relativistic mean-field (RMF) hadronic models used in the literature, regarding their behavior in the nuclear matter regime. We analyze here different kinds of such models, namely: (i) linear models, (ii) nonlinear σ^3+σ^4 models, (iii) σ^3+σ^4+ω^4 models, (iv) models containing mixing terms in the fields σand ω, (v) density dependent models, and (vi) point-coupling ones. In the finite range models, the attractive (repulsive) interaction is described in the Lagrangian density by the σ(ω) field. The isospin dependence of the interaction is modeled by the ρmeson field. We submit these sets of RMF models to eleven macroscopic (experimental and empirical) constraints, used in a recent study in which 240 Skyrme parametrizations were analyzed. Such constraints cover a wide range of properties related to symmetric nuclear matter (SNM), pure neutron matter (PNM), and both SNM and PNM.

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Quark matter equation of state and stellar properties

In this paper we study strange matter by investigating the stability window within the QMDD model at zero temperature and check that it can explain the very massive pulsar recently detected. We compare our results with the ones obtained from the MIT bag model and see that the QMDD model can explain larger masses, due to the stiffening of the equation of state.

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Particle yields in heavy ion collisions and the influence of strong magnetic fields

It is expected that the magnetic field in the surface of magnetars do not exceed $10^{15}$ G. However, in heavy ion collisions, this value is expected to be much higher. We investigate the effects of a magnetic fields varying from $10^{18}$, to $10^{20}$ G in strange matter (composed of $u$, $d$ and $s$ quarks). We model matter as a free gas of baryons and mesons under the influence of an external magnetic field. We study the effects of such strong fields through a $χ^2$ fit to some data sets of the STAR experiment. For this purpose we solve the Dirac, Rarita-Schwinger, Klein-Gordon and Proca equations subject to magnetic fields in order to obtain the energy expressions and the degeneracy for spin 1/2, spin 3/2, spin 0 and spin 1 particles, respectively. Our results show that a field of the order of $10^{19}$ G produces an improved fitting to the experimental data as compared to the calculations without magnetic field.

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