arXiv subjects

Débora P. Menezes

Publications and source records attributed to Débora P. Menezes.

At least 37 records · Page 2Linked to original sources

arXiv2023

Exotic Baryons in Hot Neutron Stars

We study the nuclear isentropic equation of state for a stellar matter composed of nucleons, hyperons, and $Δ$-resonances. We investigate different snapshots of the evolution of a neutron star, from its birth as a lepton-rich protoneutron star in the aftermath of a supernova explosion to a lepton-poor regime when the star starts cooling to a catalyzed configuration. We use a relativistic model within the mean-field approximation to describe the hot stellar matter and adopt density-dependent couplings adjusted by the DDME2 parameterization. We use baryon-meson couplings for the spin-$1/2$ baryonic octet and spin-$3/2$ decuplet determined in a unified manner relying on $\text{SU}(6)$ and $\text{SU}(3)$ symmetry arguments. We observe that $Λ$ is the dominant exotic particle in the star at different entropies for both neutrino-free and neutrino-trapped stellar matter. For a fixed entropy, the inclusion of new particles (hyperons and/or delta resonances) in the stellar matter decreases the temperature. Also, an increase in entropy per baryon ($1\;\text{to}\; 2$) with decreasing lepton number density ($0.4\;\text{to}\; 0.2$) leads to an increase in stellar radii and a decrease in its mass due to neutrino diffusion. In the neutrino transparent matter, the radii decrease from entropy per baryon $2$ to $T\,=\,0$ without a significant change in stellar mass.

nucl-th↗

arXiv2023

Anisotropic electron transport in the nuclear pasta phase

The presence of nuclear pasta is expected to modify the transport properties in the mantle of neutron stars. The non-spherical geometry of the pasta nuclear clusters leads to anisotropies in the collision frequencies, impacting the thermal and electrical conductivity. We derive analytical expressions for the anisotropic collision frequencies using the Boltzmann equation in the relaxation time approximation. The average parallel, perpendicular and Hall electrical conductivities are computed in the high-temperature regime above crustal melting, considering incoherent elastic electron-pasta scattering and randomly oriented pasta structures. Numerical values are obtained at different densities and temperatures by using the IUFSU parametrization of the non-linear Walecka model to determine the crustal structure. We find that the anisotropy of the collision frequencies grows with the length of the pasta structures and, independently of the magnetic field, the presence of rod and slab phases decreases the conductivity by more than one order of magnitude. Our numerical results indicate that, even if the pasta structures might survive above the crustal melting point, no strong anisotropies are to be expected in the conduction properties in this temperature regime, even in the presence of a very high magnetic field.

nucl-th↗

arXiv2023

Dark matter effects on hybrid star properties

In the present work we investigate the effects of dark matter (DM) on hybrid star properties. We assume that dark matter is mixed with both hadronic and quark matter and interact with them through the exchange of a Higgs boson. The hybrid star properties are obtained from equations of state calculated with a Maxwell prescription. For the hadronic matter we use the NL3* parameter set and for the quark matter, the MIT bag model with a vector interaction. We see that dark matter does not influence the phase transition points (pressure and chemical potential) but shifts the discontinuity on the energy density, which ultimately reduces the minimum mass star that contains a quark core. Moreover, it changes considerably the star family mass-radius diagrams and moves the merger polarizability curves inside the confidence lines. Another interesting feature is the influence of DM in the quark core of the hybrid stars constructed. Our results show an increase of the core radius for higher values of the dark particle Fermi momentum.

hep-ph↗

arXiv2022

The baryon coupling scheme in an unified SU(3) and SU(6) symmetry formalism

We calculate the baryon-meson coupling constants for the spin-1/2 baryonic octet and spin-3/2 decuplet in a unified approach relying on symmetry arguments such as the fact that the Yukawa couplings, present in the Lagrangian density of the Walecka-type models, must be an invariant under SU(3) and SU(6) group transformations. The coupling constants of the baryon with the scalar $σ$ meson are fixed to reproduce the known potential depths for the hyperons and $Δ$ resonances, in an approach that can be extended to all particles. We then apply the calculated coupling constants to study neutron star matter with hyperons and deltas admixed to its composition. We conclude that the $Δ^-$ is by far the most important exotic particle that can be present in the neutron star interior. It is always present, independent of the chosen parameterization, and might appear in almost every known neutron star, once its onset happens at very low density. Yet, its presence affects the astrophysical properties of the canonical 1.4 M$_\odot$ star, and, in some cases, it can even contribute to an increase in the maximum mass reached.

hep-ph↗

arXiv2022

Scientific physics events in Brazil: female participation

We have carried out a partial survey on the female participation in events organized by the Brazilian Physical Society (SBF, in Portuguese) from 2005 to 2021. Our analysis shows that the participation of women has increased over the years, reaching in some areas, the same percentage as the one observed in the SBF community (always lower that 25\%). However, the participation as members of organizing committees and as keynote speakers is always lower. Some propositions to change this inequality situation are listed.

physics.soc-ph↗

arXiv2022

Delta baryons in neutron stars

By applying a relativistic mean-field description of neutron star matter with density dependent couplings, we analyse the properties of two different matter compositions: nucleonic matter with delta baryons and nucleonic matter with hyperons and delta baryons. The delta-meson couplings are allowed to vary within a wide range of values obtained by experimental data, while the hyperon-meson couplings are fitted to hypernuclear properties. Neutron star properties with no deconfinement phase transition are studied. It is verified that many models are excluded because the effective nucleon mass becomes zero before the maximum mass configuration is attained. Hyperon-free with delta-dominated composition compact stars are possible, the deltic stars. It is found that with a convenient choice of parameters the existence of deltic stars with 80% of delta baryons at the center of the star is possible. However, the presence of hyperons lowers the delta baryon fraction to values below 20% at the center and below 30% at 2-3 saturation densities. It is discussed that in the presence of delta baryons, the hyperon softening is not so drastic because deltas couple more strongly to the $ω$-meson, and the stiffness of the equation of state is determined by the $ω$-dominance at high densities. The speed of sound reflects very well this behavior. The compactness of the pulsar RX J0720.4-3125 imposes $x_{σΔ}>x_{ωΔ}>1$ and favors $x_{ρΔ}>1$.

nucl-th↗

arXiv2022

Generalized Rastall's gravity and its effects on compact objects

We present a generalization of Rastall's gravity in which the conservation law of the energy-momentum tensor is altered, and as a result, the trace of the energy-momentum tensor is taken into account together with the Ricci scalar in the expression for the covariant derivative. Afterwards, we obtain the field equations in this theory and solve them by considering a spherically symmetric space-time. We show that the external solution has two possible classes of solutions with spherical symmetry in the vacuum in generalized Rastall's gravity, and we analyse one of them explicitly. The generalization, in contrast to constant value $k=8πG$ in general relativity, has a gravitational parameter $k$ that depends on the Rastall constant $α$. As an application, we perform a careful analysis of the effects of the theory on neutron stars using realistic equations of state (EoS) as input. Our results show that important differences on the profile of neutron stars are obtained within two representatives EoS.

gr-qc↗

arXiv2021

Hypermassive quark cores

Using a quantum hadrodynamics (QHD) and MIT based models we construct hybrid stars within the Maxwell criteria of hadron-quark phase transition. We are able to produce a hybrid star with maximum mass of 2.15$M_\odot$. Furthermore, a 2.03$M_\odot$ star with a quark core corresponding to more than $80\%$ of both, its total mass and radius, is also possible.

hep-ph↗

arXiv2021

Delta Baryons in Neutron-Star Matter under Strong Magnetic Fields

In this work, we study magnetic field effects on neutron star matter containing the baryon octet and additional heavier spin 3/2 baryons (the $Δ$'s). We make use of two different relativistic hadronic models that contain an additional vector-isovector self interaction for the mesons: one version of a relativistic mean field (RMF) model and the Chiral Mean Field (CMF) model. We find that both the additional interaction and a strong magnetic field enhance the $Δ$ baryon population in dense matter, while decreasing the relative density of hyperons. At the same time that the vector-isovector meson interaction modifies neutron-star masses very little ($<0.1~M_\odot$), it decreases their radii considerably, allowing both models to be in better agreement with observations. Together, these features indicate that magnetic neutron stars are likely to contain $Δ$ baryons in their interior.

nucl-th↗

arXiv2021

Effects of Strong Magnetic Fields on the Hadron-Quark Deconfinement Transition

The aim of the present work is to investigate the effects of strong magnetic fields on the hadron-quark phase transition point at zero temperature. To describe the hadronic phase, a relativistic mean field (RMF) model is used and to describe the quark phase a density dependent quark mass model (DDQM) is employed. As compared with the results obtained with non-magnetised matter, we observe a shift of the transition point towards higher pressures and, generally also towards higher chemical potentials. An investigation of the phase transitions that could sustain hybrid stars is also performed.

nucl-th↗

arXiv2021

Fluctuations in the pasta phase

Baryonic matter close to the saturation density is very likely to present complex inhomogeneous structures collectively known under the name of pasta phase. At finite temperature, the different geometric structures are expected to coexist, with potential consequences on the neutron star crust conductivity and neutrino transport in supernova matter. In the framework of a statistical multi-component approach, we calculate the composition of matter in the pasta phase considering density, proton fraction, and geometry fluctuations. Using a realistic energy functional from relativistic mean field theory and a temperature and isospin dependent surface tension fitted from Thomas-Fermi calculations, we show that different geometries can coexist in a large fraction of the pasta phase, down to temperatures of the order of the crystallization temperature of the neutron star crust. Quantitative estimates of the charge fluctuations are given.

nucl-th↗

arXiv2021

Modified MIT bag Models -- part I: Thermodynamic consistency, stability windows and symmetry group

In this work we study different variations of the MIT bag model. We start with the so called non-ideal bag model and discuss it in detail. Then we implement a vector interaction in the MIT bag model that simulates a meson exchange interaction and fix the quark-meson coupling constants via symmetry group theory. At the end we propose an original model, inspired by the Boguta-Bodmer models, which allows us to control the repulsion interaction at high densities. For each version of the model we obtain a stability window as predicted by the Bodmer-Witten conjecture and discuss its thermodynamic consistency.

hep-ph↗

arXiv2020

Gravitational Wave Signatures of Highly Magnetized Neutron Stars

Motivated by the recent gravitational wave detection by the LIGO-VIRGO observatories, we study the Love number and dimensionless tidal polarizability of highly magnetized stars. We also investigate the fundamental quasi-normal mode of neutron stars subject to high magnetic fields. To perform our calculations we use the chaotic field approximation and consider both nucleonic and hyperonic stars. As far as the fundamental mode is concerned, we conclude that the role played by the constitution of the stars is far more relevant than the intensity of the magnetic field and if massive stars are considered, the ones constituted by nucleons only present frequencies somewhat lower than the ones with hyperonic cores, a feature that can be used to point out the real internal structure of neutron stars. Moreover, our studies clearly indicate that strong magnetic fields play a crucial role in the deformability of low mass neutron stars, with possible consequences on the interpretation of the detected gravitational waves signatures.

nucl-th↗

arXiv2020

Short-range correlation effects on the neutron star cooling

Short range correlations (SRC) have been known to be an important aspect of nuclear theory for some time. Recent works have re-ignited interest on this topic, particularly due to the fact that it has recently been demonstrated that SRC may be responsible for breaking pairing gaps in nuclear matter. In this work we revisit the concept of SRC for beta equilibrated matter in neutron stars. We construct two equivalent models, with and without SRC and proceed to investigate the thermal evolution of stars described by such models. We show that SRC play a major role in the thermal evolution of neutron stars. It will be shown that while the SRC largely leaves the macroscopic properties of the star unaltered, it significantly alters the proton fraction, thus leading to an early onset of the direct Urca (DU) process, which in turns leads to stars exhibiting much faster cooling.

nucl-th↗

arXiv2019

Anisotropic Compact Stars in Rastall-Rainbow Gravity

In this work, we have investigated anisotropic neutron stars in the framework of Rastall-Rainbow gravity. All our calculations were computed using the IU-FSU realistic equation of state (EoS), in which was considered two cases: standard nucleonic composition and the one with the eight lightest baryons. From the neutron star masses and radii obtained we conclude that anisotropic pressure has significant consequences on the structure of stellar objects. In particular, when anisotropy is considered within the general relativity framework, it significantly modifies the maximum stellar mass. On the other hand, when Rastall-Rainbow gravity and anisotropy are simultaneously considered, they provide the best results for mass and radius values, including important astrophysical objects such as the LMXB NGC 6397 and the extremely massive pulsar millisecond MSP J0740 + 6620. Although the expected inclusion of hyperons in the nuclear model reproduces stellar masses smaller than those produced by standard nucleonic matter, we shown that the hyperon puzzle problem can be solved by including anisotropic effects on compact stars in the context of the Rastall-Rainbow gravity.

astro-ph.HE↗

arXiv2019

Bag-type Model with Fractal Structure

In this work we present a bag-type model within a non-extensive statistics applied to the description of the properties of a hadronic system with an underlying fractal structure. The non-extensive ideal gas inside the bag is determined by the grand canonical partition function from which pressure, energy and particle density as well as temperature and chemical potential are obtained for the hadronic system. These quantities are studied in the approximation of fixed mass for all bag constituents but also for discrete and continuum masses. In all cases, the freeze-out line, corresponding to the energy per particle equal to 1 GeV and the lines corresponding to a fractal structure inside the proton volume are obtained. Finally, the pressure on the bag surface of the proton is calculated and the resulting value $(0.135\, {\rm GeV})^4$ obtained.

nucl-th↗

arXiv2019

Neutron star cooling and GW170817 constraint within quark-meson coupling models

In the present work we used five different versions of the quark-meson coupling (QMC) model to compute astrophysical quantities related to the GW170817 event and to neutron star cooling process. Two of the models are based on the original bag potential structure and three versions consider a harmonic oscillator potential to confine the quarks. The bag-like models also incorporate the pasta phase used to describe the inner crust of neutron stars. We show that the pasta phase always play a minor or negligible role in all studies. Moreover, while no clear correlation between the models that satisfy the GW170817 constraints and the slope of the symmetry energy is found, a clear correlation is observed between the slope and the fact that the cooling is fast or slow, i.e., fast (slow) cooling is related to higher (lower) values of the slope. We did not find one unique model that can describe, at the same time, GW170817 constraints and give a perfect description of the possible cooling processes.

astro-ph.HE↗

arXiv2019

Combined Rastall and Rainbow theories of gravity with applications to neutron stars

The possibility of modifications on general relativity is investigated. We propose an alternative theory of gravity constructed with the combination of Rastall and Rainbow theories. The hydrostatic equilibrium equations are obtained in order to test the new theory in neutron stars, whose mass-radius diagrams are obtained using modern equations of state of nuclear matter derived from relativistic mean field models and compared with the ones computed by the Tolman-Oppenheimer-Volkoff equations. We conclude that substantial modifications are obtained even for very small alterations on the two free parameters, making the reproduction of astrophysical observations an easy task.

astro-ph.HE↗