Relativistic Hadronic Models Research Articles

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

ABSTRACTWe 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 (L0). 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 per cent confidence interval for the two cases analysed (different input ranges for L0 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 km ≤ R1.4 ≤ 12.73 km (Case 1) and 12.34 km ≤ R1.4 ≤ 13.06 km (Case 2) for the radius of the $1.4\, \mathrm{M}_\odot$ neutron star.

Delta baryons in neutron-star matter under strong magnetic fields

In this work, we study magnetic field effects on neutron star matter containing the baryon octet and additional heavier spin 3/2 baryons (the $$\varDelta $$ ’s). We make use of two different relativistic hadronic models that contain an additional vector-isovector self interaction for the mesons: one version of a relativistic mean field (RMF) model and the chiral mean field (CMF) model. We find that both the additional interaction and a strong magnetic field enhance the $$\varDelta $$ baryon population in dense matter, while decreasing the relative density of hyperons. At the same time that the vector-isovector meson interaction modifies neutron-star masses very little ( $$<0.1~\mathrm M_{\mathrm{Sun}}$$ ), it decreases their radii considerably, allowing both models to be in better agreement with observations. Together, these features indicate that magnetic neutron stars are likely to contain $$\varDelta $$ baryons in their interior.

Stellar matter with a strong magnetic field within density-dependent relativistic models

The effect of strong magnetic fields on the equation of state (EoS) for compact stars described with density-dependent relativistic hadronic models is studied. A comparison with other mean-field relativistic models is done. It is shown that the largest differences between models occur for low densities, and that the magnetic field affects the crust properties of a star, namely its extension.

RELATIVISTIC HADRONIC MATTER AND PHASE TRANSITIONS

A brief revision of different relativistic hadronic models, including the original sigma-omega model, models with nonlinear meson terms, density dependent coupling parameters and the quark-meson coupling, are presented. The inclusion of short range correlations is discussed. Dense stellar matter is described within the relativistic hadronic models introduced. We build the EoS for cold and warm hadronic and hybrid stars and discuss the star properties obtained within the different approaches. The low density thermodynamical and dynamical instabilities of stellar matter of interest for the discussion of the crust of neutron stars are investigated.

Spinodal instabilities and the distillation effect in relativistic hadronic models

Liquid-gas phase transitions in asymmetric nuclear matter give rise to a distillation effect that corresponds to the formation of droplets of high-density symmetric matter in a background of a neutron gas possibly with a very small fraction of protons. In the present work we test the model dependence of this effect. We study the spinodal instabilities of asymmetric nuclear matter within six different mean-field relativistic models with both constant and density-dependent coupling parameters. We also consider the effects of introducing the \ensuremath{\delta} meson and the nonlinear $\ensuremath{\omega}\text{\ensuremath{-}}\ensuremath{\rho}$ coupling. It is shown that the distillation effect within density-dependent models is not so efficient and is comparable to results obtained for nonrelativistic models. Thermodynamical instabilities of nuclear matter neutralized by electrons as found in stellar matter are also investigated. The high Fermi energy of electrons completely erases the instability of density-dependent models. The other models still show a small region of instability but the distillation effect completely disappears because the electron presence freezes the proton fluctuations.

QCD phase transitions from relativistic hadron models

QCD phase transitions from relativistic hadron models

QCD phase transitions from relativistic hadron models

The models of translationally invariant infinite nuclear matter in the relativistic mean field models are very interesting and simple, since the nucleon can connect only to a constant vector and scalar meson field. Can one connect these to the complicated phase transitions of QCD? For an affirmative answer to this question, one must consider models where the coupling contstants to the scalar and vector fields depend on density in a nonlinear way, since as such the models are not explicitly chirally invariant. Once this is ensured, indeed one can derive a quark condensate indirectly from the energy density of nuclear matter which goes to zero at large density and temperature. The change to zero condensate indicates a smooth phase transition.

Vacuum contributions in a chiral effective Lagrangian for nuclei.

A relativistic hadronic model for nuclear matter and finite nuclei, which incorporates nonlinear chiral symmetry and broken scale invariance, is presented and applied at the one-baryon-loop level to finite nuclei. The model contains an effective light scalar field that is responsible for the mid-range nucleon--nucleon attraction and which has anomalous scaling behavior. One-loop vacuum contributions in this background scalar field at finite density are constrained by low-energy theorems that reflect the broken scale invariance of quantum chromodynamics. A mean-field energy functional for nuclear matter and nuclei is derived that contains small powers of the fields and their derivatives, and the validity of this truncation is discussed. Good fits to the bulk properties of finite nuclei and single-particle spectra are obtained.

Finite nuclei in a relativistic model with broken chiral and scale invariance

A relativistic hadronic model that provides a realization of the broken chiral and scale invariance of quantum chromodynamics has recently been applied to nuclear matter at the mean-field level. Although the model can reproduce nuclear matter saturation, calculations of finite nuclei reveal serious deficiencies.