arXiv subjects

César V. Flores

Publications and source records attributed to César V. Flores.

5 recordsLinked to original sources

arXiv2026

Bayesian approach study of hybrid neutron stars

In this work, we explore how astronomical observations (specifically measurements of masses and radii) can constrain the presence of quark matter inside neutron stars, namely the phase transition from nuclear matter to deconfined quark matter. Our approach employs Bayesian analysis to study this constraint. In this sense to model Hadronic matter we used the relativistic mean-field approximation, for which we have selected two parameter sets: $NL3^{*}ωρ$, representing hadronic matter with nucleons only, and $EL3ωρ$ with nucleons only and $EL3ωρY$, which includes hyperons. On the other hand deconfined quark matter is modeled using the vector-MIT bag model. Also, for our purpose, the first order phase transition is implemented using the Maxwell construction. Bayesian inference is performed by optimizing three parameters: the bag constant (i.e. $B^{1/4}$), the vector coupling constant $\left(G_{v}\right)$, and the Dirac sea contribution ($b_{4}$). We found that a phase transition could exist at densities below $2.0\,n_{0}$ for both the $EL3ωρ$ and $NL3^{*}ωρ$ parametrizations. As a consequence, the inferred parameters of the vector MIT bag model, based on our likelihood function, imply hybrid stars with large quark cores.

nucl-th↗

arXiv2026

Investigating the impact of quasi-universal relations on neutron star constraints in third-generation detectors

Gravitational-wave observations of binary neutron star systems can shed light on the currently unknown dense matter equation of state. The equation of state determines a large number of neutron star properties, such as tidal deformability, radius, and quadrupole moment, several of which directly affect the emitted gravitational-wave signals. To reduce the dimensionality when computing gravitational-waves and when interpreting observational data, quasi-universal relations are commonly employed to connect different neutron star properties. However, quasi-universal relations are not exact and their use may introduce uncertainty and bias. We explore the potential biases arising from different quasi-universal relations in the third generation era: (i) the Love-Q relation connecting the spin-induced quadrupole moment and the tidal deformability, (ii) the relation between the fundamental mode frequency and the tidal deformability, and (iii) the binary Love relation. We find that for the quadrupole relation biases are only present for rapidly rotating systems, for the binary-Love relation induces moderate biases only in the next-to-leading-order tidal parameters, which can however propagate into the inferred equation of state at low masses. Regarding fundamental mode frequencies, we find that the employed relation introduces only negligible biases, while waveform systematic effects can become comparatively large. Our results highlight that while quasi-universal relations remain a useful tool within gravitational-wave analyses, careful treatment is needed to avoid biases in equation of state measurements with next-generation detectors.

gr-qc↗

arXiv2024

Gravitational wave asteroseismology of neutron stars with unified EOS: on the role of high-order nuclear empirical parameters

We analyze the sensitivity of non-radial fluid oscillation modes and tidal deformations in neutron stars to high-order nuclear empirical parameters (NEP). In particular, we study the impact of the curvature and skewness of the symmetry energy $K_{\rm sym}$, $Q_{\rm sym}$, and the skewness of the binding energy in symmetric nuclear matter $Q_{\rm sat}$. As we are interested in the possibility of gravitational wave detection by future interferometers, we consider that the tidal interaction is the driving force for the quadrupolar non-radial fluid oscillations. We have also studied the correlations between those quantities, which will be useful to understand the strong physics of gravitational wave phenomena. Our main results show that $K_{\rm sym}$ impacts the frequencies of the fundamental mode mainly for low-mass neutron stars. The NEP $Q_{\rm sym}$ and $Q_{\rm sat}$ affect the fundamental modes of intermediate and heavy neutron stars, respectively. In the case of the first pressure mode, $K_{\rm sym}$ shows a small effect, while $Q_{\rm sat}$ shows a considerable decrease in this oscillation mode independent of the neutron star mass. Similarly, for tidal deformability, the NEP $Q_{\rm sat}$ and $Q_{\rm sym}$ show a bigger impact than $K_{\rm sym}$. Given the impact of the NEP on gravitational wave phenomena and the currently large uncertainties of these parameters, the prospect of higher sensitivity in future gravitational wave detectors promise a possible new tool to constrain high-order NEP.

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arXiv2019

Consistent relativistic mean field models constrained by GW170817

We have obtained the Love number and corresponding tidal deformabilites ($Λ$) 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 $Λ_{1.4}$ and the radius of canonical stars ($R_{1.4}$). When a recently GW170817 constraint on $Λ_{1.4}$ and the corresponding radius $R_{1.4}$ is used, the majority of the models tested are shown to satisfy it.

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arXiv2018

Phase transition effects on the dynamical stability of hybrid neutron stars

We study radial oscillations of hybrid non-rotating neutron stars composed by a quark matter core and hadronic external layers. At first, we physically deduce the junction conditions that should be imposed between two any phases in these systems when perturbations take place. Then we compute the oscillation spectrum focusing on the effects of slow and rapid phase transitions at the quark-hadron interface. We use a generic MIT bag model for quark matter and a relativistic mean field theory for hadronic matter. In the case of rapid transitions at the interface we find a general relativistic version of the reaction mode which has similar properties as its classical counterpart. We also show that the usual static stability condition $\partial M/\partial ρ_c\geq 0$, where $ρ_c$ is the central density of a star whose total mass is $M$, remains always true for rapid transitions but breaks down in general for slow transitions. In fact, for slow transitions we find that the frequency of the fundamental mode can be a real number (indicating stability) even for some branches of stellar models that verify $\partial M/\partial ρ_c \leq 0$. Thus, when secular instabilities are suppressed, as expected below some critical stellar rotation rate, it would be possible the existence of twin or even triplet stars with the same gravitational mass but different radii, with one of the counterparts having $\partial M/\partial ρ_c \leq 0$. We explore some astrophysical consequences of these results.

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