Neutron stars in a class of nonlinear relativistic models

TLDR: In this paper, a class of relativistic models for nuclear matter and neutron stars which exhibits a parametrization, through mathematical constants, of the nonlinear meson-baryon couplings is introduced.

Abstract: In this work we introduce a class of relativistic models for nuclear matter and neutron stars which exhibits a parametrization, through mathematical constants, of the nonlinear meson-baryon couplings. For appropriate choices of the parameters, it recovers current quantum hadrodynamics models found in the literature: the Walecka model and Zimanyi-Moszkowski models (ZM and ZM3). For other choices of parameters, the models give very interesting and new physical results. The phenomenology of neutron stars in ZM models is presented and compared to the phenomenology obtained in other versions of the Walecka model. We have found that the ZM3 model is too soft, and predicts a very small maximum neutron star mass, $\ensuremath{\sim}{0.72M}_{\ensuremath{\bigodot}}.$ A strong similarity between the results of ZM-like models and those with exponential couplings is noted. The sensibility of the results to the specific choice of the values for the binding energy and saturation density is pointed out. Finally, we discuss the very intense scalar condensates found in the interior of neutron stars, which may lead to negative effective masses.

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TABLE II. Values of l, b, andg for different QHD models.

FIG. 8. Radial distribution of the different leptonic and baryon species in the ZM model.

TABLE III. Stellar properties for theS case:«c is the central density,M ! is the star mass,R! is the star radius,S is the scalar potential in the star center,z is a redshift;Y/A is the hyperon/baryon ratio, andNBT is the total baryonic number. All these quantities are evaluated for the neutron star with the maximum m the sequence. In addition, we have the compression modulusK and the nucleon effective massM !/M .

FIG. 4. Comparison of the compression modulus of nucl matterK with the ratioM* /M for the S and S-V cases. The box shows the range of accepted values.

FIG. 5. Neutron star mass as a function of the central densit Walecka~solid line!, ZM ~dashed line!, and ZM3~dotted line! models.

FIG. 3. Dependence of the coupling constants with thel parameter for the scalar~full lines! and scalar-vector~dotted lines! models.