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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 ω ρ ∗ 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. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the evolution of strange quark stars (SQS) from birth as proto-strange quark stars to maturity as stable SQSs at a zero temperature. We assume that self-bound free quarks form entirely the compact star and study its evolution through a series of snapshots using a density-dependent quark mass model. We consider β -equilibrated stellar matter at two major stages of the star’s evolution: neutrino trapped regime and neutrino transparent regime during the deleptonization and cooling processes of the star. We fix the entropy density per baryon and the lepton fraction to investigate the nuclear equation of state (EoS), particle distribution, temperature profile inside the star, sound velocity, polytropic index, and the structure of the star. Our results show that stars with higher neutrino concentrations are slightly more massive than the neutrino-poor ones along the evolution lines of the SQS. We obtain EoSs in agreement with the conformal boundary set through sound velocity, and also the 2 M ⊙ mass constraint for NSs was satisfied at all stages of the star’s evolution. [ABSTRACT FROM AUTHOR]

It is known that diversity matters to improve scientific excellence and that scientific events are important occasions to discuss new ideas and create networks, beyond the fact that it helps to put the work of the scientists in evidence. Hence, increasing diversity in scientific events is crucial to improve their scientific quality and help to promote minorities. In Brazil, important physics scientific events are organized by the Brazilian Physical Society (SBF, in Portuguese), and in this work, some aspects related to the participation of women in these physics events are analyzed from 2005 to 2021. The analysis shows that women's participation has increased over the years, reaching in some areas of Physics the same percentage as the one observed in the SBF community (always below 25%). However, female participation as members of organizing committees and as keynote speakers is always lower. Some proposals are listed to change the current picture of inequality. [ABSTRACT FROM AUTHOR]

The anisotropics in the pressure obtained from the energy-momentum tensor are studied for magnetized quark matter within the su(3) Nambu-Jona-Lasinio model for both β-equilibrium matter and quark matter with equal quark chemical potentials. The effect of the magnetic field on the particle polarization, magnetization, and quark matter constituents is discussed. It is shown that the onset of the s quark after chiral symmetry restoration of the u and d quarks gives rise to a special effect on the magnetization in the corresponding density range: A quite small magnetization just before the s onset is followed by a strong increase of this quantity as soon as the s quark sets in. It is also demonstrated that for B < 1018 G within the two scenarios discussed, always considering a constant magnetic field, the two components of pressure are practically coincident. [ABSTRACT FROM AUTHOR]

The non extensive thermodynamics of an ideal gas composed by bosons and/or fermions is derived from its partition function for systems with finite chemical potentials. It is shown that the thermodynamical quantities derived in the present work are in agreement with those obtained in previous works when μ ≤ m . However some inconsistencies of previous references are corrected when μ > m . A discontinuity in the first derivatives of the partition function and its effects are discussed in detail. We show that at similar conditions, the non extensive statistics provide a harder equation of state than that provided by the Boltzmann–Gibbs statistics. [ABSTRACT FROM AUTHOR]

The effect of the vector interaction on three-flavor magnetized matter is studied within the SU(3) Nambu-Jona-Lasinio quark model. We considered cold matter under a static external magnetic field within two different models for the vector interaction in order to investigate how the form of the vector interaction and the intensity of the magnetic field affect the equation of state as well as the strangeness content. It was shown that the flavor-independent vector interaction predicts a smaller strangeness content and, therefore, harder equations of state. On the other hand, the flavor-dependent vector interaction favors larger strangeness content the larger the vector coupling. We confirmed that, at low densities, the magnetic field and the vector interaction have opposite competing effects: the first one softens the equation of state while the second hardens it. Quark stars and hybrid stars subject to an external magnetic field were also studied. Larger star masses are obtained for the flavor-independent vector interaction. Hybrid stars may bare a core containing deconfined quarks if neither the vector interaction nor the magnetic field are too strong. Also, the presence of strong magnetic fields seems to disfavor the existence of a quark core in hybrid stars. [ABSTRACT FROM AUTHOR]

In this work we investigate protoneutron star properties within a modified version of the quark-meson coupling (QMC) model that incorporates an co-p 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 nonlinear Walecka model for similar values of the symmetry energy slope. Contrary to GM 1, within the QMC model 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 process could be a neutrino signal followed by a gamma ray burst. We have seen that both models can, in general, describe very massive stars. [ABSTRACT FROM AUTHOR]

We investigate the properties of mixed stars formed by hadronic and quark matter in β-equilibrium described by appropriate equations of state (EOS) in the framework of relativistic mean-field theory. The calculations were performed for T=0 and for finite temperatures and also for fixed entropies with and without neutrino trapping in order to describe neutron and proto-neutron stars. The star properties are discussed. Maximum allowed masses for proto-neutron stars are much larger when neutrino trapping is imposed. [ABSTRACT FROM AUTHOR]

In this work we revisit the quantum hadrodynamics (QHD) formalism to investigate hyperonic and hybrid stars with hyperon-meson couplings fixed via broken SU(6) group, in favor of a more general flavor group SU(3). We also employ an additional channel, the strangeness-hidden ϕ meson, which couples only to the hyperons. In hybrid stars, the quark phase is built with the SU(3) NJL model also with an additional vector channel in the Lagrangian. We found that within the models chosen the hyperon onset cannot be avoided by the quark-hadron phase transition, once the hyperon threshold always happens at lower density. Also, the contribution of the quark core in a hybrid star is more relevant to the radius than to the mass, and strongly depends on the quark equation of state. We are able to reproduce 2.21 M ⊙ hyperonic star and 2.10 M ⊙ hybrid star. Both results are in agreement with the recently detected hyper massive pulsar MSP J0740+6620. [ABSTRACT FROM AUTHOR]

The equilibrium distributions of the different pasta geometries and their linear sizes are calculated from the mean field Gibbs energy functional in symmetric nuclear matter at finite temperature. The average sizes and shapes coincide approximately with the ones predicted by a standard pasta calculation in the coexisting phase approximation, but fluctuations are additionally calculated and seen to increase with temperature and baryonic density. The different pasta shapes are shown to coexist in a wide domain of density and temperature, in qualitative agreement with the findings of large scale molecular dynamics simulations, but with a much less expensive computational cost. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 Sun ), 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. [ABSTRACT FROM AUTHOR]

We compare relativistic mean-field models with their low density expansion counterparts used to mimic nonrelativistic models by consistently expanding the baryonic scalar density in powers of the baryonic number density up to O(13/3), which goes two orders beyond the order considered in previous works. We show that, due to the nontrivial density dependence of the Dirac mass, the convergence of the expansion is very slow, and the validity of the nonrelativistic approximation is questionable even at subsaturation densities. In order to analyze the roles played by strangeness and isospin we consider n-Λ and n-p matter separately. Our results indicate that these degrees of freedom play quite different roles in the expansion mechanism and n-Λ matter can be better described by low density expansions than n-p matter in general. [ABSTRACT FROM AUTHOR]

We have investigated under which conditions hyperons (particularly Λs and Σ-s) can be found in the nuclear pasta phase. As the density and temperature are larger and the electron fraction is smaller, the probability is greater that these particles appear, but always in very small amounts. Λ hyperons only occur in gas and in smaller amounts than would occur if matter were homogeneous, never with abundancies above 10-5. The amount of Σ- in the gas is at least two orders of magnitude smaller and can be disregarded in practical calculations. [ABSTRACT FROM AUTHOR]

Nucleonic matter is described within an SU(2) extended Nambu-Jona-Lasinio (NJL) 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. A 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. [ABSTRACT FROM AUTHOR]

We study the applications of nonextensive Tsallis statistics to high energy and hadron physics. These applications include studies of p p collisions, equation of state of QCD, as well as Bose–Einstein condensation. We also analyze the connections of Tsallis statistics with thermofractals, and address some of the conceptual aspects of the fractal approach, which are expressed in terms of the renormalization group equation and the self-energy corrections to the parton mass. We associate these well-known concepts with the origins of the fractal structure in the quantum field theory. [ABSTRACT FROM AUTHOR]

Particle production yields measured in central Au-Au collision at RHIC are obtained with free Fermi and Bose gases and also with a replacement of these statistics by non-extensive statistics. For the latter calculation, a set of different parameters was used with values of the Tsallis parameter q chosen between 1.01 and 1.25, with 1.16 generating the best agreement with experimental data, an indication that non-extensive statistics may be one of the underlying features in heavy ion-collisions. [ABSTRACT FROM AUTHOR]

In this paper, 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 spacetime. 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 analyze one of them explicitly. The generalization, in contrast to constant value k = 8 π G 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. [ABSTRACT FROM AUTHOR]

We investigate compact star properties within the quark-meson-coupling model with a soft symmetry energy density dependence at large densities. In particular, the hyperon content and the mass/radius curves for the families of stars obtained within the model are discussed. The hyperon-meson couplings are chosen according to experimental values of the hyperon nuclear matter potentials, and possible uncertainties are considered. It is shown that a softer symmetry energy gives rise to stars with less hyperons, smaller radii, and larger masses. Hyperon-meson couplings may also have a strong effect on the mass of a star. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. This 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. [ABSTRACT FROM AUTHOR]

Background: The emergence of hyperon degrees of freedom in neutron star matter has been associated to first-order phase transitions in some phenomenological models, but conclusions on the possible physical existence of an instability in the strangeness sector are strongly model dependent. Purpose: The purposes of the present study are to assess whether strangeness instabilities are related to specific values of the largely unconstrained hyperon interactions and to study the effect of the strange meson couplings on phenomenological properties of neutron stars and supernova matter, once these latter are fixed to fulfill the constraints imposed by hypernuclear data. Method: We consider a phenomenological relativistic mean field model (RMF) model sufficiently simple to allow a complete exploration of the parameter space. Results: We show that no instability at supersaturation density exists for the RMF model, as long as the parameter space is constrained by basic physical requirements. This is at variance with a nonrelativistic functional, with a functional behavior fitted through ab initio calculations. Once the study is extended to include the full octet, we show that the parameter space allows reasonable radii for canonical neutron stars as well as massive stars above two-solar mass, together with an important strangeness content of the order of 30%, slightly decreasing with increasing entropy, even in the absence of a strangeness-driven phase transition. Conclusions: We conclude that the hyperon content of neutron stars and supernova matter cannot be established with present constraints, and is essentially governed by the unconstrained coupling to the strange isoscalar meson. [ABSTRACT FROM AUTHOR]

We analyze the stellar properties of the relativistic mean-field (RMF) parametrizations shown to be consistent with the recently studied constraints related to nuclear matter, pure neutron matter, symmetry energy, and its derivatives [Phys. Rev. C 90, 055203 (2014)]. Our results show that only two RMF parametrizations do not allow the emergence of the direct Urca process, important aspect regarding the evolution of a neutron star. Moreover, among all approved RMF models, fourteen of them produce neutron stars with maximum masses inside the range 1.93≤M/M⊙≤2.05, with M⊙ being the solar mass. Only three models yield maximum masses above this range and a discussion on the inclusion of hyperons is presented. Finally, we verified that the models satisfying the neutron star maximum mass constraint do not observe the squared sound velocity bound; namely, v²s<1/3, corroborating recent findings. However, the recently proposed σ-cut scheme can make the RMF models consistent with both constraints, depending on the isoscalar-vector interaction of each parametrization. [ABSTRACT FROM AUTHOR]

Background: The advent of new dedicated experimental programs on hyperon physics is rapidly boosting the field, and the possibility of synthesizing multiple strange hypernuclei requires the addition of the strangeness degree of freedom to the models dedicated to nuclear structure and nuclear matter studies at low energy. Purpose: We want to settle the influence of strangeness on the nuclear liquid-gas phase transition. Because of the large uncertainties concerning the hyperon sector, we do not aim at a quantitative estimation of the phase diagram but rather at a qualitative description of the phenomenology, as model independent as possible. Method: We analyze the phase diagram of low-density matter composed of neutrons, protons, and Λ hyperons using a relativistic mean field (RMF) model. We largely explore the parameter space to pin down generic features of the phase transition, and compare the results to ab initio quantum Monte Carlo calculations. Results: We show that the liquid-gas phase transition is only slightly quenched by the addition of hyperons. Strangeness is seen to be an order parameter of the phase transition, meaning that dilute strange matter is expected to be unstable with respect to the formation of hyperclusters. Conclusions: More quantitative results within the RMF model need improved functionals at low density, possibly fitted to ab initio calculations of nuclear and Λ matter. [ABSTRACT FROM AUTHOR]

We have obtained the Love number and corresponding tidal deformabilities (Λ) associated with the relativistic mean-field parametrizations shown to be consistent (CRMF) with the nuclear matter, pure neutron matter, symmetry energy, and its derivatives [Dutra et al., Phys. Rev. C 90, 055203 (2014)]. Our results show that CRMF models present very good agreement with the recent data from binary neutron star merger event GW170817. They also confirm the strong correlation between Λ1.4 and the radius of canonical stars (R1.4). When a recent GW170817 constraint on Λ1.4 and the corresponding radius R1.4 is used, the majority of the models tested are shown to satisfy it. [ABSTRACT FROM AUTHOR]

In this work, the low-density regions of nuclear and neutron star matter are studied. The search for the existence of nuclear pasta phases in this region is performed within the context of the quark-meson coupling (QMC) model, which incorporates quark degrees of freedom. Fixed proton fractions are considered, as well as nuclear matter in ß equilibrium at zero temperature. We discuss the recent attempts to better understand the surface energy in the coexistence phases regime and we present results that show the existence of the pasta phases subject to some choices of the surface energy coefficient. We also analyze the influence of the nuclear pasta on some neutron star properties. The equation of state containing the pasta phase will be part of a complete grid for future use in supernova simulations. [ABSTRACT FROM AUTHOR]