arXiv subjects

Franciele M. da Silva

Publications and source records attributed to Franciele M. da Silva.

At least 19 recordsLinked to original sources

arXiv2026

Charged black string immersed in a quintessence fluid and string cloud

We present a new static solution describing a charged black string immersed in a Kiselev-type quintessence fluid and a string cloud. The metric and field equations are solved for a general quintessence state parameter, with explicit results provided for the physically relevant case $w_q = -2/3$. We analyze the event-horizon structure and the Kretschmann scalar, verify energy-condition constraints, and derive thermodynamic properties including the Hawking temperature and heat capacity and the Helmholtz free energy. Finally, we investigate the existence of an exterior photon cylinder for circular null geodesics, finding that, under the parameter assumptions adopted here, no such cylinder occurs outside the outer horizon. The solution generalizes known charged black-string spacetimes by simultaneously including quintessence and a string-cloud parameter.

gr-qc↗

arXiv2026

A self-consistent single-fluid framework for neutron stars admixed with mirror dark matter

We develop a self-consistent dark matter admix neutron star framework based on a contact vector current--current interaction that couples the chemical potentials of both sectors through mutual mean-field shifts, with the dark matter (DM) fraction $F_D = N_D/N_B$ fixed as a global input parameter. This formulation provides a physically motivated alternative to fixed-density prescriptions, allowing the local DM density to follow the baryonic matter (BM) density throughout the stellar interior. As an application, we consider a mirror-DM scenario with exact symmetry between the dark and visible sectors and investigate NS matter using the NL3$ωρ$, FSU2R, NL3, and DDME2 equations of state (EOSs). We find that the amount of DM introduced through $F_D$ weakens the binding of dense matter, reduces its incompressibility, and softens the EOS, while the DM--BM interaction governs the microscopic behavior of the DM in the dense BM medium. Consequently, DM increases the central density and compactness of NSs, lowers their maximum masses, and shifts the onset of the direct Urca process to higher stellar densities. As a consequence, the onset of rapid cooling is shifted to more massive stars for models with a stiff symmetry energy and to less massive stars for models with a soft symmetry energy, depending on the extra compactness that results from the DM admixture. These results demonstrate that mirror-DM admixtures modify both the microscopic composition and macroscopic structure of NSs, with potential implications for their thermal evolution and multimessenger observational signatures.

astro-ph.HE↗

arXiv2026

Rotational effects in quark stars: comparing different models

We investigate the rotational properties of self-bound strange quark stars using two representative quark matter equations of state (EOS): the vector MIT bag model and the density-dependent quark mass (DDQM) model. Through general-relativistic calculations of uniformly rotating sequences, we analyze their mass--radius relations, moments of inertia, quadrupole moments, surface redshifts, Keplerian frequencies, and energy components. A central result of this work is the full decomposition of the stellar energy budget in rotating strange stars, separating gravitational, internal, rotational, and binding energy contributions. Rotation amplifies the intrinsic EOS differences: the MIT model supports more massive ($M_{\max} \gtrsim 3.3\,M_\odot$) compact stars with larger moments of inertia and greater resistance to deformation, while the DDQM model produces larger radii, less massive stars limited by mass-shedding at lower frequencies. Combined measurements of mass, radius, and frequency can thus break the EOS degeneracy; massive, rapidly rotating pulsars favors MIT-like EOS, whereas larger radii in canonical stars point to a DDQM-like model. These rotational observables, soon to be tightly constrained by NICER and next-generation gravitational-wave detectors, offer a means to test the existence and composition of self-bound quark matter in compact stars.

astro-ph.HE↗

arXiv2026

Dark Matter Heating in Evolving Proto-Neutron Stars: A Two-Fluid Approach

Neutron stars (NSs) provide a unique laboratory to probe dark matter (DM) through its gravitational imprint on stellar evolution. We use a two-fluid framework with non-annihilating, asymmetric DM, both fermionic and bosonic, that interacts with ordinary matter (OM) solely through gravity. Within this framework, we track protoneutron stars (PNSs) across their thermal and compositional evolution via quasi-static modeling over the Kelvin--Helmholtz cooling timescale. We uncover a distinct thermal signature: DM cores deepen the gravitational potential, compressing and heating the baryonic matter, while extended DM halos provide external support, leading to cooling of the stellar matter. In contrast, hyperons and other exotic baryons soften the equation of state similarly to DM cores but reduce, rather than increase, the temperature. DM thus alters both temperature and particle distribution profiles in ways that provide a clear diagnostic of its presence. DM cores also enhance compactness and shift hyperon onset, with the strongest effects during deleptonization and neutrino-transparent phases due to reduced neutrino pressure contributions. Consequently, this early thermal evolution, observable through supernova neutrino light curves and young pulsar cooling curves, offers a direct, testable probe of DM in NSs.

astro-ph.HE↗

arXiv2026

White dwarf structure in $f(R,T,L_m)$ gravity: beyond the Chandrasekhar mass limit

In this work, we investigate the relativistic structure of white dwarfs (WDs) within the framework of modified gravity theory $f(R, T, L_m) = R + αT L_m$, which introduces a non-minimal coupling between matter and curvature. Using a realistic equation of state (EoS) that includes contributions from a relativistic degenerate electron gas and ionic lattice effects, we solve the modified Tolman-Oppenheimer-Volkoff (TOV) equations for two standard choices of the matter Lagrangian density: $L_m = p$ and $L_m = -ρ$. We show that the extra $αTL_m$ term significantly alters the mass-radius relation of WDs, especially at high central densities $( ρ_c \gtrsim 10^8 - 10^9\,\rm g/cm^3)$, allowing for stable super-Chandrasekhar configurations. In particular, depending on the sign and magnitude of the parameter $α$, the maximum mass can increase or decrease, and in some regimes, the usual critical point indicating the transition from stability to instability disappears. Our findings suggest that $f(R,T,L_m)$ gravity provides a viable framework to explain the existence of massive WDs beyond the classical Chandrasekhar limit. Using Bayesian inference with WD observational data, we further constrain the coupling parameter $α$ for the two choices of the Lagrangian density $L_m$.

gr-qc↗

arXiv2025

Hyperons and $Δ$'s in rotating protoneutron stars: Local properties

The structural evolution of rotating protoneutron stars encodes essential information about their observable signatures, while microscopic properties provide complementary knowledge to advance observational investigations. Using a relativistic mean-field model with density-dependent couplings that account for temperature and particle composition, we investigate rotation, neutrino-emission-driven changes in angular momentum, particle distributions, temperature profiles, and sound speed to probe the internal dynamics of protoneutron star matter. Additionally, we track the evolution of macroscopic quantities such as energy distribution and gravitational mass and establish direct links between microphysics and global evolution. Extending the framework of Phys. Rev. D 112, 023007 (2025), which focuses on the global properties of rotating protoneutron star evolution, our results reveal that protoneutron star deformation and thermal evolution are governed by angular momentum, mass, and composition. Exotic matter (hyperons and $Δ$-resonances) and rapid rotation enhance deformation leading to a reduction in core temperature, whereas slowly rotating stars like PSR J0740$+$6620 remain nearly spherical. Our predicted equatorial radii for PSR J0740$+$6620, $13.0\ \mathrm{km} < R_e < 13.5\ \mathrm{km}$, are consistent with NICER measurements. These findings constrain the EoS, requiring a self-consistent treatment of rotation, mass-dependent compression, and composition-driven modeling to accurately model protoneutron star evolution in the context of multi-messenger astrophysics.

astro-ph.HE↗

arXiv2025

Hyperons and $Δ$'s in rotating protoneutron stars: Global properties

Rotation plays an important role in the evolution of most types of stars, in particular, it can have a strong influence on the evolution of a newly born proto-neutron star. In this study, we investigate the effects of rotation on four snapshots of the evolution of proto-neutron stars with hyperons and $Δ$-resonances in their cores, from birth as neutrino-rich objects to maturity as cold, catalyzed neutron stars. We focus on the effects of uniform rotation on the macroscopic structure of the star at three rotational frequencies -- 346.53 Hz, 716 Hz, and the Kepler frequency. Our investigation indicates that the impact of rotation at frequencies of $346.53$~Hz and $716$~Hz causes minor changes in the maximum gravitational mass but leads to significant changes in the stellar radius, particularly for stars with masses smaller than $2$~\msun. However, we observe drastic changes in the star's mass and radius when considering the Kepler frequency. In addition, we investigate other relevant characteristics of the rotating proto-neutron stars as they evolve such as the moment of inertia, compactness, central temperature, and Kerr parameter. Our results suggest that the inclusion of new degrees of freedom in the stellar core lead the star to be more sensitive to rotational dynamics, owing to an increase in compactness, a decrease in the central temperature, and a decrease in the moment of inertia.

hep-ph↗

arXiv2025

The sound of quintessence: analogue Kiselev acoustic black holes

In this work, we demonstrate that the geometry of a spherically symmetric black hole surrounded by a Kiselev anisotropic fluid can be effectively mimicked by an experimental setup as the ones used to investigate some physical phenomena associated with acoustic black holes. Thus, we construct the metric describing Kiselev acoustic black holes by using the Gross--Pitaevskii theory and present a general analytical solution that encompasses, as particular cases, several classes of geometries associated with black holes. This unified framework allows for the description of a wide variety of analogue spacetimes, including new analogue geometries that have not been previously explored in the literature. Then, we examine the behavior of scalar field perturbations in this background by solving the massless Klein--Gordon equation. Depending on the boundary conditions between the acoustic event horizon and infinity, we obtain the quasinormal and quasibound spectra. This study opens up avenues for experimental investigation within the context of analog gravity models, by offering new possibilities to simulate and study black hole phenomena in laboratory settings.

gr-qc↗

arXiv2025

Strongly Interacting Quark Matter in Massive Quark Stars

This paper investigates the properties of strongly coupled matter at high baryon densities ($ρ_B$) in quark stars (QSs). The QS model is based on the density-dependent quark mass (DDQM) framework, modified (MDDQM) by enhancing the single-gluon interaction to generate higher repulsive pressure. The model parameters are constrained using Bayesian inference, incorporating observational data from the pulsars HESS J1731$-$347, PSR J0030$+$0451, PSR J0740$+$6620, and PSR J0952$-$0607. Our results show that the MDDQM model produces QSs with higher mass and compactness compared to the DDQM model. Among the four MDDQM parameterizations studied, two yield maximum star masses of 1.86 and 2.10 $\rm M_\odot$ and exhibit near-conformal behavior in the underlying quark matter (QM). The other two parameterizations, yielding QS masses of 2.30 and 2.37 $\rm M_\odot$, correspond to a stronger interaction in the underlying QM. These findings provide important insights into the equation of state of deconfined QM and its implications for the structure and stability of QSs.

nucl-th↗

arXiv2025

Constraining the Generalized Tolman-Oppenheimer-Volkoff (GTOV) equation with Bayesian analysis

In this work, we constrain the values of the parameters of the Generalized Tolman-Oppenheimer-Volkoff (GTOV) equation through Bayesian inference. We use the mass and radius data from the Neutron Star Interior Composition Explorer (NICER) for PSR J0740$+$6620 and PSR J0030$+$0451, as well as the mass, radius, and dimensionless tidal deformability from the gravitational wave (GW) events GW190814 and GW170817. We use two distinct parameterizations of the extended non-linear Walecka model (eNLW) with and without hyperons. The GTOV employed for the study contains additional free parameters with different physical motivations. Two possible scenarios are considered in our analysis: conservative and speculative. In the first case, we take into account the most reliable neutron star (NS) data from NICER and the GW170817 event. In the second case, we consider the possibility that the compact object with a mass of $2.54 M_{\odot}$ in the GW190814 event is an NS. Our findings show significant improvements in the physical quantities analyzed, leading to better agreement with the observational data compared to the results obtained using the TOV equation.

astro-ph.HE↗

arXiv2025

Supernova Remnants with Mirror Dark Matter and Hyperons

For the first time, we use relativistic mean-field (RMF) approximation with density-dependent couplings, adjusted by the DDME2 parameterization, to investigate the effects of dark matter on supernova remnants. We calculate the nuclear equation of state for nuclear and dark matter separately, under the thermodynamic conditions related to the evolution of supernova remnants. A mirrored model is adopted for dark matter, and its effect on remnant matter is studied using a two-fluid scenario. At each stage of the remnant evolution, we assume that dark and ordinary matter have the same entropy and lepton fraction, and a fixed proportion of dark matter mass fraction is added to the stellar matter to observe its effects on some microscopic and macroscopic properties of the star. We observe that dark matter in the remnant core reduces the remnant's maximum mass, radius, and tidal deformability. Moreover, dark matter heats the remnant matter and alters particle distributions, thereby decreasing its isospin asymmetry and increasing the sound speed through the matter.

hep-ph↗

arXiv2024

Black hole solutions surrounded by anisotropic fluid in f(T,T) gravity

In this work, we investigate some extensions of the Kiselev black hole solutions in the context of $f(\mathbb{T},\CMcal{T})$ gravity. By mapping the components of the Kiselev energy-momentum tensor into the anisotropic energy-momentum tensor and assuming a particular form of $f(\mathbb{T},\CMcal{T})$, we obtain exact solutions for the field equation in this theory that carries dependence on the coupling constant and on the parameter of the equation of state of the fluid. We show that in this scenario of modified gravity some new structure is added to the geometry of spacetime as compared to the Kiselev black hole. We analyse the energy conditions, mass, horizons and the Hawking temperature considering particular values for the parameter of the equation of state.

gr-qc↗

arXiv2024

A Bayesian study of quark models in view of recent astrophysical constraints

In this work, we perform a comparative analysis between the density-dependent quark model and the vector MIT bag model using Bayesian analysis. We use the equations of state generated by these two models to describe quark stars. We impose four recent observational astrophysical constraints on both models to determine their model-dependent parameters in an optimized manner assuming that the compact objects observed are composed entirely of self-bound quarks. The restrictions are aimed at producing stars with maximum masses $2 - 2.35$ M$_\odot$ and a mass-radii diagram compatible with the observed pulsars: PSR J0740+6620, PSR J0952-0607, PSR J0030+0451 and the compact object XMMU J173203.3-344518. With this analysis, the parameter dependence of the nuclear equation of state (EoS) of both models is restricted.

nucl-th↗

arXiv2024

Proto-strange quark stars from density-dependent quark mass model

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$_\odot$ mass constraint for NSs was satisfied at all stages of the star's evolution.

nucl-th↗

arXiv2023

Neutron stars in the context of $f$($\mathbb{T}$,$\mathcal{T}$) gravity

In this work, we investigate the existence of neutron stars (NS) in the framework of $f$($\mathbb{T}$,$\mathcal{T}$) gravity, where $\mathbb{T}$ is the torsion tensor and $\mathcal{T}$ is the trace of the energy-momentum tensor. The hydrostatic equilibrium equations are obtained, however, with $p$ and $ρ$ quantities passed on by effective quantities $\bar{p}$ and $\barρ$, whose mass-radius diagrams are obtained using modern equations of state (EoS) of nuclear matter derived from relativistic mean field models and compared with the ones computed by the Tolman-Oppenheimer-Volkoff (TOV) equations. Substantial changes in the mass-radius profiles of NS are obtained even for small changes in the free parameter of this modified theory. The results indicate that the use of $f$($\mathbb{T}$,$\mathcal{T}$) gravity in the study of NS provides good results for the masses and radii of some important astrophysical objects, as for example, the low-mass X-ray binary (LMXB) NGC 6397 and the pulsar of millisecond PSR J0740+6620. In addition, radii results inferred from the Lead Radius EXperiment (PREX-2) can also be described for certain parameter values.

astro-ph.HE↗

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

Effects of modified dispersion relations on free Fermi gas: equations of state and applications in astrophysics

Deformed dispersion relations are considered in the study of equations of state of Fermi gas with applications to compact objects. Different choices of deformed energy relations are used in the formulation of our model. As a first test, we consider a relativistic star with a simple internal structure. The mass-radius diagrams obtained suggest a positive influence of deformed Fermi gas, depending of the functions employed. In addition, we comment on how realistic equations of state, in which interactions between nucleons are taken into account, can be addressed.

physics.gen-ph↗

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↗