arXiv subjects

Odilon Lourenço

Publications and source records attributed to Odilon Lourenço.

At least 19 recordsLinked to original sources

arXiv2026

Structure and astrophysical properties of dark energy admixed neutron stars

The presence of a dark energy (DE) core, made of a Chaplygin dark fluid, is capable of influencing the diverse observable properties of neutron stars (NSs). However, there is also the possibility that NSs could contain a mixture of ordinary nuclear matter and DE. In this perspective, we propose an equation of state (EoS) that includes both normal matter and DE, where a free parameter $f$ quantifies the ratio of DE density with respect to the total energy density. As expected, in the limit $f \rightarrow 0$ we recover the already known results corresponding to pure nuclear matter. Remarkably, increasing this fraction $f$ leads to a softer EoS and thus strongly favors the fulfillment of the causality condition. As a consequence of our mass--radius results, the central compact object in HESS J1731-347 can be satisfactorily described as a DE admixed NS. For sufficiently high stellar masses, our calculations further indicate that both the gravitational redshift and the fundamental nonradial oscillation frequency increase significantly with an increasing DE fraction, whereas the opposite trend is observed for the total gravitational mass and tidal deformability. As is typical for compact stars composed purely of ordinary matter, we find that in our DE admixed stellar models the central density corresponding to the maximum-mass configuration coincides with the point at which the squared radial vibration frequency vanishes. Moreover, higher DE concentrations lead to enhanced stability of these configurations.

gr-qc↗

arXiv2026

Massive cold hybrid stars in a modified Polyakov-Nambu-Jona-Lasinio model

We propose a modified Polyakov-loop Nambu--Jona-Lasinio (mPNJL) model in which the Polyakov potential is given by an explicit dependence on the quark chemical potential, allowing it to remain finite at zero temperature and thus to describe the confinement-deconfinement transition in cold dense matter. Combining this modified quark sector with hadronic equations of state via a Maxwell construction, we find that, depending on the model parameters, the equation of state can exhibit either two phase transitions, from hadronic matter to confined quark matter and subsequently to deconfined quark matter, or a single transition directly from hadronic to deconfined quark matter or from hadronic to confined quark matter. Stable massive cold hybrid stars with only confined and/or deconfined quark phase are obtained. We systematically examine how the parameters of the modified Polyakov potential and the quark vector interactions control the location of these transitions, and find that repulsive vector interactions are essential to obtain a stable quark core. Hybrid stars with confined and/or a deconfined core can reach maximum masses above $2M_\odot$, provided a sufficiently stiff hadronic equation of state is used at low density. In the core of the maximum-mass configurations, the speed of sound shows variations at finite baryon densities, with c$_s^2(μ)$ departing from the asymptotic conformal value c$_s^2$ = 1/3 in confined core stars. These variations serve as a diagnostic of the equation-of-state stiffness while remaining fully consistent with causality and thermodynamic stability. This work establishes the qualitative role of each model parameter in shaping hybrid-star structure.

hep-ph↗

arXiv2026

Effects of short-range correlations at high densities on neutron stars with and without DM content: role of the repulsive self-interaction

In this work, we investigate how short-range correlations affect relativistic hadronic models at high densities, with direct consequences for the structure of neutron stars, both with and without dark matter content. Two versions of the model are examined: one with vector self-interactions up to second order ($ω_0^2$) and another including a fourth-order term ($ω_0^4$). We show that SRC tend to soften the equation of state when only the quadratic term is present, but produce a noticeable stiffening once the $ω_0^4$ term is included. The corresponding Tolman-Oppenheimer-Volkoff solutions for pure neutron stars indicate that short-range correlations reduce the maximum mass in the first case but increase it in the second. Extending the analysis to stars containing a fermionic dark matter component, within the two-fluid formalism, we verify that the same features appear in the respective mass-radius diagrams. In particular, the decrease of the maximum mass with increasing dark matter fraction is partly compensated by the SRC effects in the hadronic sector for the model with the fourth-order term. In all cases, the resulting parametrizations are consistent with recent astrophysical constraints, including the joint NICER-XMM-Newton analyses of the pulsars PSR J0030+0451 and PSR J0740+6620, as well as the gravitational-wave event GW190425.

nucl-th↗

arXiv2026

The nucleardatapy toolkit for simple access to experimental nuclear data, astrophysical observations, and theoretical predictions

Systematic comparisons across theoretical predictions for the properties of dense matter, nuclear physics data, and astrophysical observations (also called meta-analyses) are performed. Existing predictions for symmetric nuclear and neutron matter properties are considered, and they are shown in this paper as an illustration of the present knowledge. Asymmetric matter is constructed assuming the isospin asymmetry quadratic approximation. It is employed to predict the pressure at twice saturation energy-density based only on nuclear-physics constraints, and we find it compatible with the one from the gravitational-wave community. To make our meta-analysis transparent, updated in the future, and to publicly share our results, the Python toolkit \texttt{nucleardatapy} is described and released here. Hence, this paper accompanies \texttt{nucleardatapy}, which simplifies access to nuclear-physics data, including theoretical calculations, experimental measurements, and astrophysical observations. This Python toolkit is designed to easily provide data for: i) predictions for uniform matter (from microscopic or phenomenological approaches); ii) correlation among nuclear properties induced by experimental and theoretical constraints; iii) measurements for finite nuclei (nuclear chart, charge radii, neutron skins or nuclear incompressibilities, etc.) and hypernuclei (single particle energies); and iv) astrophysical observations. This toolkit provides data in a unified format for easy comparison and provides new meta-analysis tools. It will be continuously developed, and we expect contributions from the community in our endeavor.

nucl-th↗

arXiv2025

Non-Radial Oscillation Modes in Hybrid Stars with Hyperons and Delta Baryons

We study the effects of hyperons, delta baryons, and quark matter phase transitions on $f$-mode oscillations in neutron stars. Using the density-dependent relativistic mean-field model (DDME2) for the hadronic phase and the density-dependent quark mass (DDQM) model for the quark phase, we construct hadronic and hybrid equations of state (EoSs) consistent with astrophysical constraints. Including hyperons and delta baryons soften the EoS, reducing maximum mass, while phase transition to the quark matter further softens the EoS, decreasing the speed of sound and hence the maximum mass. We confirm the well-known overestimation of $f$-mode frequencies by the Cowling approximation (by about 10-30\%) compared to full General Relativity calculation, and show that this discrepancy persists across models including hyperons, $Δ$ baryons, and a phase transition to quark matter. While the discrepancy generally decreases with stellar mass, it increases near the maximum mass in the presence of a phase transition compared to EoSs without this phenomenology. We derive universal relations connecting the frequencies of the $f$-mode to the average density, compactness, and tidal deformability, finding significant deviations due to hyperons and delta baryons. These deviations could provide distinct observational signatures in gravitational wave data, offering new insights into dense matter physics and advancing gravitational wave asteroseismology of neutron star interiors. Empirical relations for mass-scaled and radius-scaled frequencies are also provided, highlighting the importance of GR calculations for accurate modeling.

astro-ph.HE↗

arXiv2025

Asymmetric warm nuclear matter described by Gogny and Skyrme-version models

In this work, we perform a detailed study of the thermodynamical properties of asymmetric nuclear matter at finite temperatures by means of the Gogny force, with a particular focus on its D1 family. We emphasize the investigation of the liquid-gas phase transition with the respective analysis of phase-coexistence boundaries (binodal sections) and instability regions (spinodal contours). Furthermore, the phenomenon of isospin distillation, intrinsically related to the unstable part of the system, is also described. In order to estimate the impact of the finite range of the nuclear interaction, for each Gogny parametrization we provide a respective zero-range Skyrme version, for which the free parameters of the model are obtained with the aim of reproducing at zero temperature the same saturation density, binding energy, incompressibility, isoscalar effective mass, isovector effective mass, symmetry energy, and symmetry energy slope. As a main result, we verify systematic deviations between the Gogny models and their Skyrme-version models, particularly at higher temperatures, where the Skyrme-version parametrizations exhibit reduced binodal and spinodal regions.

nucl-th↗

arXiv2025

Strange stars admixed with dark matter: equiparticle model in a two fluid approach

In this work, we explore the possible scenario of strange stars admixed with fermionic or bosonic dark matter. For the description of the ``visible'' sector, we use a specific phenomenological quark model that takes into account in-medium effects for the quark masses through a suitable baryonic density dependence, in which the free parameters are chosen from the analysis of the stellar matter stability window (parametrizations presenting lower energy per baryon than iron nuclei). In the case of the dark sector, we investigate the predictions of fermionic and bosonic models. In the former, we consider a spin $1/2$ dark particle, and the latter is described by a dark scalar meson. Both models present a repulsive vector interaction, particularly important for the bosonic model since it helps avoid the collapse of the star due to the lack of degeneracy pressure. Our results point out possible stable strange stars configurations in agreement with data from the NASA NICER measurements of the pulsars PSR J0030+0451 and PSR J0740+6620, including the latest observational data, as well as the observed HESS J1731-347 mass-radius relationship. As another feature, we find stars with dark matter halo configurations for lower values of the dark particle mass.

astro-ph.HE↗

arXiv2024

Strongly interacting matter in extreme magnetic fields

Magnetic fields are ubiquitous across different physical systems of current interest; from the early Universe, compact astrophysical objects and heavy-ion collisions to condensed matter systems. A proper treatment of the effects produced by magnetic fields during the dynamical evolution of these systems, can help to understand observables that otherwise show a puzzling behavior. Furthermore, when these fields are comparable to or stronger than Λ_QCD, they serve as excellent probes to help elucidate the physics of strongly interacting matter under extreme conditions of temperature and density. In this work we provide a comprehensive review of recent developments on the description of QED and QCD systems where magnetic field driven effects are important. These include the modification of meson static properties such as masses and form factors, the chiral magnetic effect, the description of anomalous transport coefficients, superconductivity in extreme magnetic fields, the properties of neutron stars, the evolution of heavy-ion collisions, as well as effects on the QCD phase diagram. We describe recent theory and phenomenological developments using effective models as well as LQCD methods. The work represents a state-of-the-art review of the field, motivated by presentations and discussions during the "Workshop on Strongly Interacting Matter in Strong Electromagnetic Fields" that took place in the European Centre for Theoretical Studies in Nuclear Physics and Related Areas (ECT*) in the city of Trento, Italy, September 25-29, 2023.

nucl-th↗

arXiv2024

Dark energy effects on realistic neutron stars

By considering realistic equations of state (EoSs) to describe the ordinary matter of the stellar crust, in this study, we explore the effect of a dark energy core, made of Chaplygin Dark Fluid (CDF), on neutron stars (NSs). To accomplish this purpose, we solve the stellar structure equations and investigate the impact of the CDF parameters on the several macroscopic properties of NSs such as mass-radius ($M-R$) relation, and tidal deformabilities of a single star and of a binary system, the latter being of great importance when analyzing gravitational-wave signals coming from the merger of such compact objects. We also present an analysis of the radial oscillation modes for the rapid phase transition, with the aim of distinguishing regions consisting of dynamically stable stars from those of unstable ones. Specifically, our outcomes reveal that an increase in the energy density jump (controlled by a parameter $α$) leads to an increase in the radial stability of the NS with a CDF core. Furthermore, our theoretical results are consistent with the observational $M-R$ measurements of millisecond pulsars from NICER data and tidal deformability constraints from the GW170817 event.

gr-qc↗

arXiv2024

Surface and curvature tensions of relativistic models

In the present paper, we show a simple method to obtain fittings for the surface and curvature tensions. The method uses the nuclear mass of a spherical fully ionized atom and a simple expression for the binding energy such that a least square fit is found when confronted with the Atomic Mass Evaluation (AME) 2020. The fittings are then used to evaluate the pasta phase free energy per particle, which is confronted with the one obtained with a Thomas-Fermi fitting. The results are very encouraging and suggest that this recipe can be safely used whenever the surface and curvature tensions are necessary.

nucl-th↗

arXiv2024

Nucleonic models at finite temperature with in-medium effective fields

We perform a calculation of dense and hot nuclear matter where the mean interaction between nucleons is described by in-medium effective fields and where we employ analytical approximations of the Fermi integrals. We generalize a previous work where we have addressed the case of the Fermi gas model with in-medium effective mass. In the present work, we fully treat the in-medium interaction by considering both its contribution to the in-medium effective fields, which can be subsumed by the mass in some cases, and to the potential term. Our formalism is general and could be applied to relativistic and nonrelativistic approaches. It is illustrated for different popular models -- Skyrme, nonlinear, and density-dependent relativistic mean-field models --, but also for the metamodel, and it provides a clear understanding of the in-medium correction to the pressure, which is present in the case of the Skyrme and metamodel but is not for the relativistic ones. For the Fermi integrals, we compare the analytical approximation to the, so-called, ``exact'' numerical calculations in order to quantitatively estimate the accuracy of the approximation.

nucl-th↗

arXiv2023

Quark confinement in an equiparticle quark model: application to stellar matter

We perform an improvement in a thermodynamical consistent model with density dependent quark masses ($m'_{u,d,s}$) by introducing effects of quark confinement/deconfinement phase transition, at high density regime and zero temperature, by means of the traced Polyakov loop ($Φ$). We use realistic values for the current quark masses, provided by the Particle Data Group, and replace the constants of the interacting part of $m'_{u,d,s}$ by functions of $Φ$, leading to a first order phase transition structure, for symmetric and stellar quark matter, with $Φ$ being the order parameter. We show that the improved model points out the direction of the chiral symmetry restoration due to the emergence of a deconfined phase. In another application, we construct quark stars mass-radius profiles, obtained from this new model, and show to be possible to satisfy recent astrophysical observational data coming from the LIGO and Virgo Collaboration, and the NICER mission concerning the millisecond pulsars PSR J0030+0451, and PSR J0740+6620.

astro-ph.HE↗

arXiv2023

Do short range correlations inhibit the appearance of the nuclear pasta?

It is well known that strongly correlated neutron-proton pairs, the short-range correlations (SRC), can modify many of the nuclear properties. In this work we have introduced, for the first time, short range correlations in the calculation of the nuclear pasta phase at zero temperature and checked how they affect its size and internal structure. We have used two different parameterizations of relativistic models in a mean field approximation and the coexistence phase approximation as a first estimation of the effects. We have seen that for very asymmetric neutron-proton-electon matter, the pasta phase shrinks considerably as compared with the results without SRC and all internal structures vanish, except the simple spherically symmetric one, the droplets. Our results indicate a possible disappearance of these complicated structures as the temperature increases.

nucl-th↗

arXiv2023

Finite temperature description of Fermi gases with in-medium effective mass

We investigate Fermi gases at finite temperature for which the in-medium effective mass may not be constant as a function of the density, the temperature, or the chemical potential. We suggest a formalism that separates the terms for which the mass is constant from the terms which explicitly treat the correction due to the in-medium effective mass. We employ the ensemble equivalence in infinite matter in order to treat these different terms. Our formalism is applied in nuclear matter and we show its goodness by comparing it to an exact treatment based on the numerical calculation of the Fermi integrals.

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

Low-energy nuclear physics and global neutron star properties

We address the question of the role of low-energy nuclear physics data in constraining neutron star global properties, e.g., masses, radii, angular momentum, and tidal deformability, in the absence of a phase transition in dense matter. To do so, we assess the capacity of 415 relativistic mean field and non-relativistic Skyrme-type interactions to reproduce the ground state binding energies, the charge radii and the giant monopole resonances of a set of spherical nuclei. The interactions are classified according to their ability to describe these characteristics and we show that a tight correlation between the symmetry energy and its slope is obtained providing $N=Z$ and $N\ne Z$ nuclei are described with the same accuracy (mainly driven by the charge radius data). By additionally imposing the constraints from isobaric analog states and neutron skin radius in $^{208}$Pb, we obtain the following estimates: $E_{sym,2}=31.8\pm 0.7$ MeV and $L_{sym,2}=58.1\pm 9.0$ MeV. We then analyze predictions of neutron star properties and we find that the 1.4$M_\odot$ neutron star (NS) radius lies between 12 and 14 km for the "better" nuclear interactions. We show that i) the better reproduction of low-energy nuclear physics data by the nuclear models only weakly impacts the global properties of canonical mass neutron stars and ii) the experimental constraint on the symmetry energy is the most effective one for reducing the uncertainties in NS matter. However, since the density region where constraints are required are well above densities in finite nuclei, the largest uncertainty originates from the density dependence of the EDF, which remains largely unknown.

nucl-th↗

arXiv2021

Tidal deformability of strange stars and the GW170817 event

In this work we consider strange stars formed by quark matter in the color-flavor-locked (CFL) phase of color superconductivity. The CFL phase is described by a Nambu-Jona-Lasinio model with four-fermion vector and diquark interaction channels. The effect of the color superconducting medium on the gluons are incorporated into the model by including the gluon self-energy in the thermodynamic potential. We construct parametrizations of the model by varying the vector coupling $G_V$ and comparing the results to the data on tidal deformability from the GW170817 event, the observational data on maximum masses from massive pulsars such as the MSP J0740+6620, and the mass/radius fits to NICER data for PSR J003+0451. Our results points out to windows for the $G_V$ parameter space of the model, with and without gluon effects included, that are compatible with all these astrophysical constraints, namely, $0.21<G_V/G_S<0.4$, and $0.02<G_V/G_S<0.1$, respectively. We also observe a strong correlation between the tidal deformabilites of the GW170817 event and $G_V$. Our results indicate that strange stars cannot be ruled out in collisions of compact binaries from the structural point of view.

astro-ph.HE↗

arXiv2021

Analysis of critical parameters for nonrelativistic models in symmetric nuclear matter

In this work we have analyzed several features of symmetric nuclear matter (SNM) at finite temperature described by different zero- and finite-range nonrelativistic families of models, namely, Skyrme, Gogny, Momentum-dependent interaction (MDI), Michigan three-range Yukawa (M3Y) and Simple Effective Interaction (SEI). We have calculated the critical parameters (CP) associated to the liquid-gas phase coexistence for nuclear matter from these parametrizations and show that they are in agreement with their experimental and theoretical values obtained in the literature. Our study also points out to a strong evidence of universality presented by the hadronic models, namely, model independence in the gaseous phase and distinguishability among different interactions in the liquid phase. We have performed a correlation study among different CP and SNM properties. Such studies involving different finite range interactions are scarce in literature. The analyzed models show an overall increasing trend of the critical temperature as a function of critical pressure.

nucl-th↗