arXiv subjects

C. H. Lenzi

Publications and source records attributed to C. H. Lenzi.

At least 19 recordsLinked to original sources

arXiv2025

Holographic hybrid stars with slow phase transitions

The $D_3$-$D_7$ holographic model is used to describe the core of the hybrid star, composed by quark matter, while its crust is modeled from a hadronic relativistic mean field (RMF) model capable of reproducing low-energy nuclear physics data as well as some astrophysical observations. The $D_3$-$D_7$ brane configuration and the RMF model lead to an equation of state that is used to solve the Tolman-Oppenheimer-Volkoff equations. For different model parameters, the mass-radius diagram is presented. The conditions for the dynamic stability of stellar configurations are discussed, considering the radial oscillation criterion for hybrid stars with slow phase transitions. Strikingly, it is shown that the models generate stable star configurations with a core of quarks. We compare our results with NICER observational data for the pulsars PSR J0030+0451 and PSR J0740+6620 and show that the compact stars generated from this method fall within the corresponding observational regions.

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arXiv2024

Quark stars in $D_3$-$D_7$ holographic model

This work investigates static and dynamical quark star properties within a $D_3-D_7$ holographic model. We solve the Tolman-Oppenheimer-Volkoff equations for the quark matter equation of state obtained from the brane configuration. We determine the mass-radius diagram for a range of model parameters and compare with recent NICER observational data for the pulsars PSR J$0030+0451$ and PSR J$0740+6620$. Motivated by the GW170817 event detected by the LIGO-Virgo collaboration, we also calculate the tidal deformability parameter obtained for each component of the binary star system. We show that quark stars composed of flavor-independent quark matter derived from the $D_3-D_7$ holographic model are not able to satisfy simultaneously the LIGO-Virgo and NICER astrophysical bounds.

hep-ph↗

arXiv2024

Gravitational wave asteroseismology of dark matter hadronic stars

The influence of the dark matter mass~($M_χ$) and the Fermi momentum~($k_{F}^{\dm}$) on the $f_0$-mode oscillation frequency, damping time parameter, and tidal deformability of hadronic stars are studied by employing a numerical integration of hydrostatic equilibrium, nonradial oscillation, and tidal deformability equations. The matter inside the hadronic stars follows the NL3* equation of state. We obtain that the influence of $M_χ$ and $k_F^{\dm}$ is observed in the $f_0$-mode, damping tome parameter, and tidal deformability. Finally, the correlation between the tidal deformability of the GW$170817$ event with $M_χ$ and $k_F^{\dm}$ are also investigated.

hep-ph↗

arXiv2023

Bayesian analysis of a relativistic hadronic model constrained by recent astrophysical observations

We use Bayesian analysis in order to constrain the equation of state for nuclear matter from astrophysical data related to the recent measurements from the NICER mission, LIGO/Virgo collaboration, and probability distributions of mass and radius from other 12 sources, including thermonuclear busters, and quiescent low-mass X-ray binaries. For this purpose, we base our study on a relativistic hadronic mean field model including an $ω-ρ$ interaction. Our results indicate optimal ranges for some bulk parameters at the saturation density, namely, effective mass, incompressibility, and symmetry energy slope ($L_0$). For instance, we find $L_0 = 50.79^{+15.16}_{-9.24}$ MeV (Case 1) and $L_0 = 75.06^{+8.43}_{-4.43}$ MeV (Case 2) in a $68\%$ confidence interval for the 2 cases analyzed (different input ranges for $L_0$ related to the PREX-II data). The respective parametrizations are in agreement with important nuclear matter constraints, as well as observational neutron star data, such as the dimensionless tidal deformability of the GW170817 event. From the mass-radius curves obtained from these best parametrizations, we also find the ranges of $11.97 \mbox{ km}\leqslant R_{1.4}\leqslant 12.73 \mbox{ km}$ (Case 1) and $12.34 \mbox{ km}\leqslant R_{1.4}\leqslant 13.06 \mbox{ km}$ (Case 2) for the radius of the $1.4M_\odot$ neutron star.

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arXiv2023

Hybrid stars with reactive interfaces: analysis within the Nambu-Jona-Lasinio model

It has been shown recently that quark-hadron conversions at the interface of a hybrid star may have a key role on the dynamic stability of the compact object. In this work we perform a systematic study of hybrid stars with reactive interfaces using a model-agnostic piecewise-polytropic hadronic equation of state and the Nambu-Jona-Lasinio model for three-flavor quark matter. For the hadronic phase we use a soft, an intermediate and a stiff parametrization that match at $1.1 n_0$ {with predictions} based on chiral effective field theory (cEFT) interactions. In the NJL Lagrangian we include scalar, vector and 't Hooft interactions. The vector coupling constant $g_{v}$ is treated as a free parameter. We also consider that there is a split between the deconfinement and the chiral phase transitions which is controlled by changing the conventional value of the vacuum pressure $-Ω_{0}$ in the NJL thermodynamic potential by $-\left(Ω_{0}+δΩ_{0}\right)$, being $δΩ_{0}$ a free parameter. We analyze the mass-radius ($M$-$R$) relation in the case of rapid ($τ\ll 1 \, \mathrm{ms}$) and slow ($τ\gg 1 \, \mathrm{ms}$) conversions, being $τ$ the reaction timescale. In the case of slow interface reactions we find $M$-$R$ curves with a cusp at the maximum mass point where a pure hadronic branch and a slow-stable hybrid star (SSHS) branch coincide. We find that the length of the slow-stable branch grows with the increase of the transition density and the energy density jump at the hadron-quark interface. We calculate the tidal deformabilities of SSHSs and analyse them in the light of the GW170817 event.

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arXiv2023

The Design Strain Sensitivity of the Schenberg Spherical Resonant Antenna for Gravitational Waves

The main purpose of this study is to review the Schenberg resonant antenna transfer function and to recalculate the antenna design strain sensitivity for gravitational waves. We consider the spherical antenna with six transducers in the semi dodecahedral configuration. When coupled to the antenna, the transducer-sphere system will work as a mass-spring system with three masses. The first one is the antenna effective mass for each quadrupole mode, the second one is the mass of the mechanical structure of the transducer first mechanical mode and the third one is the effective mass of the transducer membrane that makes one of the transducer microwave cavity walls. All the calculations are done for the degenerate (all the sphere quadrupole mode frequencies equal) and non-degenerate sphere cases. We have come to the conclusion that the 'ultimate' sensitivity of an advanced version of Schenberg antenna (aSchenberg) is around the standard quantum limit (although the parametric transducers used could, in principle, surpass this limit). However, this sensitivity, in the frequency range where Schenberg operates, has already been achieved by the two aLIGOs in the O3 run, therefore, the only reasonable justification for remounting the Schenberg antenna and trying to place it in the sensitivity of the standard quantum limit would be to detect gravitational waves with another physical principle, different from the one used by laser interferometers. This other physical principle would be the absorption of the gravitational wave energy by a resonant mass like Schenberg.

astro-ph.IM↗

arXiv2022

Dark particle mass effects on neutron star properties from a short-range correlated hadronic model

In this work we study a relativistic mean-field (RMF) hadronic model, with nucleonic short-range correlations (SRC) included, coupled to dark matter (DM) through the Higgs boson. We study different parametrizations of this model by running the dark particle Fermi momentum, and its mass in the range of $50$ GeV $\leqslant M_χ\leqslant 500$ GeV, compatible with experimental spin-independent scattering cross-sections. By using this RMF-SRC-DM model, we calculate some neutron star quantities, namely, mass-radius profiles, dimensionless tidal deformabilities, and crustal properties. Our findings show that is possible to construct RMF-SRC-DM parametrizations in agreement with constraints provided by LIGO and Virgo collaboration (LVC) on the GW170817 event, and recent observational data from the NICER mission. Furthermore, we show that the increase of $M_χ$ favors the model to attain data from LVC regarding the tidal deformabilities. Higher values of $M_χ$ also induce a reduction of the neutron star crust (mass and thickness), and cause a decrease of the crustal fraction of the moment of inertia ($I_{\rm{\tiny crust}}/I$). Nevertheless, we show that some RMF-SRC-DM parametrizations still exhibit $I_{\rm{\tiny crust}}/I>7\%$, a condition that explains the glitch activity in rotation-powered pulsars such as the Vela one. Therefore, dark matter content can also be used for describing such a phenomenon.

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arXiv2022

Dark matter effects on tidal deformabilities and moment of inertia in a hadronic model with short-range correlations

In this work we study the outcomes related to dimensionless tidal deformability $(Λ)$ obtained through a relativistic mean-field (RMF) hadronic model including short-range correlations (SRC) and dark matter (DM) content [Phys. Rev. D 105, 023008 (2022)]. As a dark particle candidate, we use the lightest neutralino interacting with nucleons through the Higgs boson exchange. In particular, we test the model against the constraints regarding the observation of gravitational waves from the binary neutron star merger GW170817 event provided by LIGO and Virgo collaboration (LVC). We show that $Λ$ decreases as the dark particle Fermi momentum ($k_F^{DM}$) increases. This feature favors the RMF-SRC-DM model used here to satisfy the limits of $Λ_{1.4}=190^{+390}_{-120}$ ($Λ$ of a $1.4M_\odot$ neutron star), and $\tildeΛ=300^{+420}_{-230}$ given by the LVC. We also show that as $k_F^{DM}$ increases, $Λ_1$ and $Λ_2$, namely, tidal deformabilities of the binary system, are also moved to the direction of the GW170817 observational data. Finally, we verify that the inclusion of DM in the system does not destroy the \mbox{$I$-Love} relation (correlation between $Λ$ and dimensionless moment of inertia, $\bar{I}$). The observation data for $\bar{I}_\star\equiv\bar{I}(M_\star)=11.10^{+3.68}_{-2.28}$, with $M_\star=1.338M_\odot$, is attained by the RMF-SRC-DM model.

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arXiv2021

PNJL model at zero temperature: three-flavor case

We propose a three-flavor version of the Polyakov-Nambu-Jona-Lasino (PNJL) model at zero temperature regime, by implementing a traced Polyakov loop ($Φ$) dependence in the scalar, vector and 't Hooft channel strengths. We study the thermodynamics of this model, named as PNJL0, with special attention for the first order confinement/deconfinement phase transition for which $Φ$ is the order parameter. For the symmetric quark matter case, an interesting feature observed is a strong reduction of the constituent strange quark mass ($M_s$) at the chemical potential related to point where deconfinement takes place. The emergence of $Φ$ favors the restoration of chiral symmetry even for the strange quark. We also investigate the charge neutral system of quarks and leptons in weak equilibrium. As an application, we construct a hadron-quark phase transition with a density dependent hadronic model coupled to the SU(3) PNJL0 model. In this case, the quark side is composed by deconfined particles. This approach is used to determine mass-radius profiles compatible with recent data from the Neutron Star Interior Composition Explorer (NICER) mission.

hep-ph↗

arXiv2021

Neutron star crustal properties from relativistic mean-field models and bulk parameters effects

We calculate crustal properties of neutron stars, namely, mass ($M_{\rm crust}$), radius ($R_{\rm crust}$) and fraction of moment of inertia ($ΔI/I$) from parametrizations of hadronic relativistic mean-field (RMF) model consistent with symmetric and asymmetric nuclear matter constraints, as well as some stellar boundaries. We verify which one are also in agreement with restrictions of $ΔI/I \geqslant 1.4\%$ and $ΔI/I \geqslant 7\%$ related to the glitching mechanism observed in pulsars, such as the Vela one. The latter constraint explains the glitches phenomenon when entrainment effects are taken into account. Our findings indicate that these parametrizations pass in the glitching limit for a neutron star mass range of $M\leqslant 1.82M_\odot$ ($ΔI/I \geqslant 1.4\%$), and $M\leqslant 1.16M_\odot$ ($ΔI/I \geqslant 7\%$). We also investigate the influence of nuclear matter bulk parameters on crustal properties and find that symmetry energy is the quantity that produces the higher variations on $M_{\rm crust}$, $R_{\rm crust}$, and~$ΔI/I$. Based on the results, we construct a particular RMF parametrization able to satisfy $ΔI/I \geqslant 7\%$ even at $M=1.4M_\odot$, the mass value used to fit data from the softer component of the Vela pulsar X-ray spectrum. The model also presents compatibility with observational data from PSR J1614-2230, PSR J0348+0432, and MSP J0740+6620 pulsars, as well as, with data from the Neutron Star Interior Composition Explorer (NICER) mission.

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arXiv2020

Neutron stars in $f(\mathcal{R,T})$ gravity using realistic equations of state in the light of massive pulsars and GW170817

In this work we investigate neutron stars (NS) in $f(\mathcal{R,T})$ gravity for the case $R+2λ\mathcal{T}$, $\mathcal{R}$ is the Ricci scalar and $\mathcal{T}$ the trace of the energy-momentum tensor. The hydrostatic equilibrium equations are solved considering realistic equations of state (EsoS). The NS masses and radii obtained are subject to a joint constrain from massive pulsars and the event GW170817. The parameter $λ$ needs to be negative as in previous NS studies, however we found a minimum value for it. The value should be $|λ|\lesssim0.02$ and the reason for so small value in comparison with previous ones obtained with simpler EsoS is due to the existence of the NS crust. The pressure in theory of gravity depends on the inverse of the sound velocity $v_s$. Since, $v_s$ is low in the crust, $|λ|$ need to be very small. We found that the increment in the star mass is less than $1\%$, much smaller than previous ones obtained not considering the realistic stellar structure, and the star radius cannot become larger, its changes compared to GR is less than $3.6\%$ in all cases. The finding that using several relativistic and non-relativistic models the variation on the NS mass and radius are almost the same for all the EsoS, manifests that our results are insensitive to the high density part of the EsoS. It confirms that stellar mass and radii changes depend only on crust, where the EoS is essentially the same for all the models. The NS crust effect implying very small values of $|λ|$ does not depend on the theory's function chosen, since for any other one the hydrostatic equilibrium equation would always have the dependence $1/v_s$. Finally, we highlight that our results indicate that conclusions obtained from NS studies done in modified theories of gravity without using realistic EsoS that describe correctly the NS interior can be unreliable.

astro-ph.HE↗

arXiv2020

GW170817 constraints analyzed with Gogny forces and momentum-dependent interactions

A set of equations of state obtained from finite-range Gogny forces and momentum-dependent interactions is used to investigate the recent observation of gravitational waves from the binary neutron star merger GW170817 event. For this set of interactions, we have calculated the neutron star tidal deformabilities (related to the second Love number), the mass-radius diagram, and the moment of inertia~($I$). The $I$-Love relation has been verified. We also have found strong correlations among the tidal deformability of the canonical neutron star, its radius, and the derivatives of the nuclear symmetry energy at the saturation density. Most of the obtained results are located within the constraints of the tidal deformabilities extracted from the GW170817 detection.

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arXiv2020

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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arXiv2019

Density-dependent van der Waals model under the GW170817 constraint

We propose a density-dependent function for the attractive interaction in the original van der Waals model to correctly describe the flow constraint at the high-density regime of the symmetric nuclear matter. After a generalization to asymmetric nuclear matter, it was also possible to study the stellar matter regime from this new model. The mass-radius relation for neutron stars under $β$-equilibrium is found to agree with recent X-ray observations. The neutron star masses supported against gravity, obtained from some parametrizations of the model, are in the range of $(1.97-2.07)M_{\odot}$, compatible with observational data from the PSR J0348+0432 pulsar. Furthermore, we verify the reliability of the model in predicting tidal deformabilities of the binary system related to the GW170817 neutron star merger event and find a full agreement with the new bounds obtained by the LIGO/Virgo collaboration.

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arXiv2012

Hybrid stars in the light of the massive pulsar PSR J1614-2230

We perform a systematic study of hybrid star configurations using several parametrizations of a relativistic mean-field hadronic EoS and the NJL model for three-flavor quark matter. For the hadronic phase we use the stiff GM1 and TM1 parametrizations, as well as the very stiff NL3 model. In the NJL Lagrangian we include scalar, vector and 't Hooft interactions. The vector coupling constant $g_v$ is treated as a free parameter. We also consider that there is a split between the deconfinement and the chiral phase transitions which is controlled by changing the conventional value of the vacuum pressure $- Ω_0$ in the NJL thermodynamic potential by $- (Ω_0 + δΩ_0)$, being $δΩ_0$ a free parameter. We find that, as we increase the value of $δΩ_0$, hybrid stars have a larger maximum mass but are less stable, i.e. hybrid configurations are stable within a smaller range of central densities. For large enough $δΩ_0$, stable hybrid configurations are not possible at all. The effect of increasing the coupling constant $g_v$ is very similar. We show that stable hybrid configurations with a maximum mass larger than the observed mass of the pulsar PSR J1614-2230 are possible for a large region of the parameter space of $g_v$ and $δΩ_0$ provided the hadronic equation of state contains nucleons only. When the baryon octet is included in the hadronic phase, only a very small region of the parameter space allows to explain the mass of PSR J1614-2230. We compare our results with previous calculations of hybrid stars within the NJL model. We show that it is possible to obtain stable hybrid configurations also in the case $δΩ_0=0$ that corresponds to the conventional NJL model for which the pressure and density vanish at zero temperature and chemical potential.

astro-ph.SR↗

arXiv2010

Compact stars with a quark core within NJL model

An ultraviolet cutoff dependent on the chemical potential as proposed by Casalbuoni {\it et al} is used in the su(3) Nambu-Jona-Lasinio model. The model is applied to the description of stellar quark matter and compact stars. It is shown that with a new cutoff parametrization it is possible to obtain stable hybrid stars with a quark core. A larger cutoff at finite densities leads to a partial chiral symmetry restoration of quark $s$ at lower densities. A direct consequence is the onset of the $s$ quark in stellar matter at lower densities and a softening of the equation of state.

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arXiv2010

Investigation of the existence of hybrid stars using Nambu-Jona-Lasinio models

We investigate the hadron-quark phase transition inside neutron stars and obtain mass-radius relations for hybrid stars. The equation of state for the quark phase using the standard NJL model is too soft leading to an unstable star and suggesting a modification of the NJL model by introducing a momentum cutoff dependent on the chemical potential. However, even in this approach, the instability remains. In order to remedy the instability we suggest the introduction of a vector coupling in the NJL model, which makes the EoS stiffer, reducing the instability. We conclude that the possible existence of quark matter inside the stars require high densities, leading to very compact stars.

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arXiv2010

Quarks stars in SU(2) Nambu-Jona-Lasinio model with vector coupling

In this work we study the Nambu-Jona-Lasinio model in the SU (2) version with repulsive vector coupling and apply it to quark stellar matter. We discuss the influence of the vector interaction on the equation of state (EoS) and study quark stars that are composed of pure quark matter with two flavors. We show that, increasing the vector coupling, we obtain more massive stars with larger radii for the same central energy density.

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