arXiv subjects

Kauan D. Marquez

Publications and source records attributed to Kauan D. Marquez.

10 recordsLinked to original sources

arXiv2024

Radial Oscillations in Hybrid Stars with Slow Quark Phase Transition

This study investigates the radial oscillations of hybrid neutron stars, characterized by a composition of hadronic external layers and a quark matter core. Utilizing a density-dependent relativistic mean-field model that incorporates hyperons and baryons for describing hadronic matter, and a density-dependent quark model for quark matter, we analyze the ten lowest eigenfrequencies and their corresponding oscillation functions. Our focus lies on neutron stars with equations-of-state involving N, N + $Δ$, N + H, and N + H + $Δ$, featuring a phase transition to quark matter. Emphasizing the effects of a slow phase transition at the hadron-quark interface, we observe that the maximum mass is attained before the fundamental mode's frequency decreases for slow phase transitions. This observation implies the stability of stellar configurations with higher central densities than the maximum mass, called Slow Stable Hybrid Stars (SSHSs), even under small radial perturbations. The length of these SSHS branch depends upon the energy density jump between two phases and the stiffness of the quark EoS.

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arXiv2024

Radial Oscillations of Hybrid Stars and Neutron Stars including Delta baryons: The Effect of a Slow Quark Phase Transition

We study radial oscillations of hybrid neutron stars composed of hadronic external layers followed by a quark matter core. We employ a density-dependent relativistic mean-field model including hyperons and $Δ$ baryons to describe hadronic matter, and a density-dependent quark model for quark matter. We obtain the ten lowest eigenfrequencies and the corresponding oscillation functions of N, N+$Δ$, N+H, and N+H+$Δ$ equations-of-state with a phase transition to the quark matter at 1.4 and 1.8 ${M_{\odot}}$, focusing on the effects of a slow phase transition at the hadron-quark interface. We observe that the maximum mass is reached before the fundamental mode's frequency vanishes for slow phase transitions, suggesting that some stellar configurations with higher central densities than the maximum mass remain stable even when they undergo small radial perturbations. Future gravitational wave detectors and multi-messenger astronomy, complemented by robust microscopic models enabling exploration of various neutron star compositions, including hyperon content, are anticipated to impose precise limitations on the equation of state of baryonic matter under high-density conditions.

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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.

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arXiv2023

Radial Oscillations in Neutron Stars with Delta Baryons

We investigate the effect of $Δ$ baryons on the radial oscillations of neutron and hyperon stars, employing a density-dependent relativistic mean-field model. The spin-$3/2$ baryons are described by the Rarita-Schwinger Lagrangian density. The baryon-meson coupling constants for the spin-3/2 decuplet and the spin-1/2 baryonic octet are calculated using a unified approach relying on the fact that the Yukawa couplings present in the Lagrangian density of the mean-field models must be invariant under the SU(3) and SU(6) group transformations. We calculate the 20 lowest eigenfrequencies and corresponding oscillation functions of $Δ$-inclusive nuclear (N+$Δ$) and hyperonic matter (N+H+$Δ$) by solving the Sturm-Liouville boundary value problem and also verifying its validity. We see that the lowest mode frequencies for N+$Δ$ and N+H EoSs are higher as compared to the pure nucleonic matter because of the deltas and hyperons present. Furthermore, the separation between consecutive modes increases with the addition of hyperons and $Δ$s.

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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

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 $x_{ρΔ}>1$.

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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.

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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.

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arXiv2019

Hadron-quark phase transition: the QCD phase diagram and stellar conversion

Different extensions of the Nambu-Jona-Lasinio model, known to satisfy expected QCD chiral symmetry aspects, are used to investigate a possible hadron-quark phase transition at zero temperature and to build the corresponding binodal sections. We have shown that the transition point is very sensitive to the model parameters and that both pressure and chemical potential increase drastically with the increase of the vector interaction strength in the quark sector. Within the same framework, the possibility of quark and hybrid star formation is analyzed. The same conclusions drawn before with respect to the coexistence pressure and chemical potentials are reinforced. We conclude that even if a transition from a metastable hadronic star to a quark star is thermodinamically possible, it is either energetically forbidden or gives rise to a blackhole. Nevertheless, conversions from metastable to hybrid stars are possible, but the mass difference between both compact objects is very small, never larger than 0.2 M$_\odot$.

astro-ph.HE↗

arXiv2017

Phase transition in compact stars: nucleation mechanism and $γ$-ray bursts revisited

We have revisited the nucleation process based on the Lifshitz-Kagan theory, which is the underlying mechanism of conversion of a pulsar constituted of hadronic matter to a quark star. We have selected appropriate models that have been tested against experimental and observational constraints to restrict the model arbitrariness present in previous investigations. The phase transition pressures and chemical potentials have been identified and afterwards, the tunneling probabilities and the nucleation time were computed. The critical pressures for which the half life of the metastable hadronic phase is one year were obtained. Even with the restrictions imposed to the selection of models, the results remained model dependent, but we found that the tunneling that makes possible the appearance of stable matter requires an overpressure that is practically independent of the quark matter bag constant. Finally, we have confirmed that the nucleation process can be one of the causes of gamma-ray bursts.

astro-ph.HE↗