arXiv subjects

César O. V. Flores

Publications and source records attributed to César O. V. Flores.

6 recordsLinked to original sources

arXiv2026

Magnetic pressure anisotropy in ultra-dense white dwarfs: Landau quantization and neutronization effects

Strong magnetic fields modify the thermodynamics of white dwarf (WD) matter by quantizing the transverse motion of degenerate electrons into Landau levels and splitting the pressure into components parallel and perpendicular to the magnetic field. We investigate how this microscopic pressure anisotropy affects ultra-dense WD sequences when Coulomb lattice contributions, electron capture thresholds, neutron drip limits, and nuclear composition are treated consistently in the equation of state (EoS). The stellar equilibrium structure is obtained by solving an anisotropic extension of the Tolman--Oppenheimer--Volkoff (TOV) equations, where $P_r = P_\parallel$ and $P_t = P_\perp$ denote the radial and tangential pressures, respectively. We compare the post-electron-capture branches with their corresponding pre-capture sequences for pure $^{12}\rm{C}$, $^{16}\rm{O}$, $^{20}\rm{Ne}$, and $^{24}\rm{Mg}$ compositions, as well as for fixed 50/50 C/O, Ne/O, and Mg/Ne mixtures. The EoS predicts $P_\perp < P_\parallel$ in density ranges where only a few Landau levels are occupied. Consequently, pressure anisotropy shifts the stellar sequences toward smaller radii, with only minor changes in the maximum masses. We also find that post-capture configurations cannot be interpreted from the mass--radius plane alone, since the corresponding $M(ρ_c)$ curves reveal unstable portions after the maximum mass is reached. Our results show that strong magnetic fields significantly reduce the radii of low-mass WDs, yielding better agreement with the observational data available in the Montreal White Dwarf Database and suggesting that future high-precision observations of massive magnetic WDs could help assess the role of magnetic pressure anisotropy in determining their masses and radii.

astro-ph.SR↗

arXiv2026

Examining the influence of anisotropy on the fundamental mode of nonradial oscillation in neutron stars on a complete general relativistic scheme

The anisotropic influence on the $f$-mode frequency of oscillations and dimensionless tidal deformability of neutron stars is analyzed by employing the nonradial oscillation equations for the complete general relativity frame and tidal deformability equations, which are derived and modified from their standard form to introduce the anisotropic factor. The fluid inside the compact star obeys an equation of state constructed by matching microscopic nuclear and perturbative QCD calculations through a piecewise polytropic interpolating scheme. For the anisotropic profile, we use a local anisotropy which is regular along the whole star and vanishes both at the center and on the star's surface. We show that the $f$-mode oscillation frequency and dimensionless tidal deformability are noticeably affected by anisotropy. Finally, we investigate the correlation between the dimensionless tidal deformability inferred from the GW$170817$ event and the anisotropy parameter.

gr-qc↗

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↗

arXiv2024

Gravitational wave seismology of charged strange stars in the Cowling approximation: the fluid pulsation modes

In this work we study, within the framework of Cowling approximation, the effect of the electric charge on the gravitational wave frequency of fluid oscillation modes of strange quark stars. For this purpose, the dense matter of the stellar fluid is described by the MIT bag model equation of state (EoS), while for the electric charge profile, we consider that the electric charge density is proportional to the energy density. We find that the gravitational wave frequencies change with the increment of electric charge; these effects are more noticeable at higher total mass values. We obtain that the $f$-mode is very sensitive to the change in the electric charge of the star. Furthermore, in the case of the $p_1$ mode, the effect of the electric charge is not very significant. Our results reveal that the study of the fundamental pulsation mode of an electrically charged compact star is very important in distinguishing whether compact stars could contain electric charge. We also employ another electric charge distribution profile that follows a power law, and it is found that the $f$-mode change is more noticeable than the $p_1$-mode when the electric charge is incremented.

astro-ph.SR↗

arXiv2024

Neutron stars in $f(R,L_m,T)$ gravity

This study explores the behavior of compact stars within the framework of $f(R,L_m,T)$ gravity, focusing on the functional form $f(R,L_m,T) = R + αTL_m$. The modified Tolman-Oppenheimer-Volkoff (TOV) equations are derived and numerically solved for several values of the free parameter $α$ by considering both quark and hadronic matter -- described by realistic equations of state (EoSs). Furthermore, the stellar structure equations are adapted for two different choices of the matter Lagrangian density (namely, $L_m= p$ and $L_m= -ρ$), laying the groundwork for our numerical analysis. As expected, we recover the traditional TOV equations in General Relativity (GR) when $α\rightarrow 0$. Remarkably, we found that the two choices for $L_m$ have appreciably different effects on the mass-radius diagrams. Results showcase the impact of $α$ on compact star properties, while final remarks summarize key findings and discuss implications, including compatibility with observational data from NGC 6397's neutron star. Overall, this research enhances comprehension of $f(R,L_m,T)$ gravity's effects on compact star internal structures, offering insights for future investigations.

gr-qc↗

arXiv2023

Imprints of the nuclear symmetry energy slope in gravitational wave signals emanating from neutron stars

We investigate possible traces of the nuclear symmetry energy slope ($L$) in the gravitational wave emission of neutron stars. For fixed stellar mass values, we examine how the slope influences the stellar radius, compactness, the tidal deformability, the frequency of the quadrupole fundamental fluid mode, and the damping time of the mode due to the gravitational wave emission. We demonstrate that all these physical quantities are sensitive to the slope and could potentially impose significant constraints on it.

hep-ph↗