Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userSound velocity and tidal deformability in compact stars
89
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The sound velocity $v_s$ and dimensionless tidal deformability $Lambda$ are analyzed using the pseudo-conformal model we developed before. In contrast to the conclusion obtained in the previous works in the literature, our model with the upper bound of the sound velocity $v_s = 1/sqrt{3}$, the so-called conformal sound velocity, set in at a { density relevant to compact stars} $gsim 2 n_0$ where $n_0$ is the normal nuclear matter density, can accommodate {it all} presently established nuclear matter and compact-star properties including the maximum star-mass constraint $ simeq 2.3 M_odot$. This observation is associated with a possible emergence of pseudoconformal structure in compact star matter---in which the trace of energy-momentum tensor is a nearly density-independent nonzero constant---brought in by a topology change at $2.0 lesssim n_{1/2}/n_0 lesssim 4.0$ commensurate with a possible change of degrees of freedom from hadrons.
rate research
Read More
In an early work, we applied a QCD-based equation of state to the study of the stellar structure of self-bound strange stars, obtaining sequences with maximum masses larger than two solar masses and radii ranging from 8 to 12 Km. In this work, we update the previous calculations and compare them with the most recent data, including the very recent determination of the mass and radius of the massive pulsar PSR J0740+6620 performed by the NICER and XMM-Newton Collaborations. Our equation of state is similar to the MIT bag model one, but it includes repulsive interactions, which turn out to be essential to reproduce the accumulated experimental information. We find that our EOS is still compatible with all astrophysical observations but the parameter window is now narrower.
With a light dilaton $sigma$ and the light-quark vector mesons $V=(rho,omega)$ incorporated into an effective scale-invariant hidden local symmetric Lagrangian, scale-chiral symmetry -- hidden in QCD -- arises at a high density, $n_{1/2}$, as an emergent symmetry, a phenomenon absent in standard chiral perturbative approaches but highly relevant for massive compact stars. What takes place as the density increases beyond $n_{1/2}sim 2n_0$ in compressed baryonic matter is (1) a topology change from skyrmions to half-skyrmions, (2) parity doubling in the nucleon structure, (3) the maximum neutron star mass $Msimeq 2.01 M_{odot}$ and the radius $Rsimeq 12.0$ km and (4) the sound velocity $v_s^2/c^2simeq 1/3$ due to the vector manifestation (VM) fixed point of $rho$ and a walking dilaton condensate, which is intricately connected to the source of the proton mass.
In this work we consider strange stars formed by quark matter in the color-flavor-locked (CFL) phase of color superconductivity. The CFL phase is described by a Nambu-Jona-Lasinio model with four-fermion vector and diquark interaction channels. The effect of the color superconducting medium on the gluons are incorporated into the model by including the gluon self-energy in the thermodynamic potential. We construct parametrizations of the model by varying the vector coupling $G_V$ and comparing the results to the data on tidal deformability from the GW170817 event, the observational data on maximum masses from massive pulsars such as the MSP J0740+6620, and the mass/radius fits to NICER data for PSR J003+0451. Our results points out to windows for the $G_V$ parameter space of the model, with and without gluon effects included, that are compatible with all these astrophysical constraints, namely, $0.21<G_V/G_S<0.4$, and $0.02<G_V/G_S<0.1$, respectively. We also observe a strong correlation between the tidal deformabilites of the GW170817 event and $G_V$. Our results indicate that strange stars cannot be ruled out in collisions of compact binaries from the structural point of view.
The radii and tidal deformabilities of neutron stars are investigated in the framework of relativistic mean-field (RMF) model with different density-dependent behaviors of symmetry energy. To study the effects of symmetry energy on the properties of neutron stars, an $omega$ meson and $rho$ meson coupling term is included in a popular RMF Lagrangian, i.e. the TM1 parameter set, which is used for the widely used supernova equation of state (EoS) table. The coupling constants relevant to the vector-isovector meson, $rho$, are refitted by a fixed symmetry energy at subsaturation density and its slope at saturation density, while other coupling constants remain the same as the original ones in TM1 so as to update the supernova EoS table. The radius and mass of maximum neutron stars are not so sensitive to the symmetry energy in these family TM1 parameterizations. However, the radii at intermediate mass region are strongly correlated with the slope of symmetry energy. Furthermore, the dimensionless tidal deformabilities of neutron stars are also calculated within the associated Love number. We find that its value at $1.4 M_odot$ has a linear correlation to the slope of symmetry energy being different from the previous studied. With the latest constraints of tidal deformabilities from GW170817 event, the slope of symmetry energy at nuclear saturation density should be smaller than $60$ MeV in the family TM1 parameterizations. This fact supports the usage of lower symmetry energy slope for the update supernova EoS, which is applicable to simulations of neutron star merger. Furthermore, the analogous analysis are also done within the family IUFSU parameter sets. It is found that the correlations between the symmetry energy slope with the radius and tidal deformability at $1.4 M_odot$ have very similar linear relations in these RMF models.
We compute the tidal deformabilities for neutron star merger for equations of state with a strong first order phase transition producing a new separate branch in the mass-radius diagram. A case is found where all three possible pairs of combinations between these two neutron star branches are present for the total mass of $M=2.7M_odot$ of the observed merger event GW170817. It is demonstrated that the plot of the two tidal deformabilities $Lambda_1$ and $Lambda_2$ of the binary neutron star can show up to three separate branches. We propose that the future detections of neutron star merger events with the same value for $Lambda_1$ but different values of $Lambda_2$ serve as a signal for the existence of a strong first order phase transition in neutron star matter.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
