Tensor and Coulomb-exchange terms in the relativistic mean-field model with δ -meson and isoscalar-isovector coupling

Abstract

Tensor couplings and Coulomb-exchange terms in the relativistic mean-field (RMF) model impact the neutron skin thickness of nuclei [N. Liliani, A. M. Nugraha, J. P. Diningrum, and A. Sulaksono, Phys. Rev. C 93, 054322 (2016)], and a significantly thicker skin of $^{208}\mathrm{Pb}$ predicted by PREX-II leads to the existence of a phase transition in the interior of neutron stars (NSs) [F. J. Fattoyev, J. Piekarewicz, and C. J. Horowitz, Phys. Rev. Lett. 120, 172702 (2018)]. In this work, we revisit the effects of tensors and Coulomb-exchange terms within the RMF model with the $\ensuremath{\delta}$-meson and isovector-isoscalar coupling on finite nuclei. We also perform a systematic investigation of the implicit effect of both terms on the nuclear matter and NS properties. We confirmed in our previous work [N. Liliani, A. M. Nugraha, J. P. Diningrum, and A. Sulaksono, Phys. Rev. C 93, 054322 (2016)] that the roles of tensor couplings, Coulomb exchange, and isovector-isoscalar coupling on the bulk properties of finite nuclei are crucial. Conversely, the $\ensuremath{\delta}$-meson term's inclusion yields no significant effect on the bulk properties of finite nuclei. The tensor couplings and Coulomb-exchange terms implicitly influence the isoscalar and isovector parts of nuclear matter. By contrast, the $\ensuremath{\delta}$-meson and isovector-isoscalar coupling significantly impact the isovector parts of nuclear matter predictions. Except for the binding energy and the equation of state of pure neutron matter in low-density cases, the nuclear matter property predictions of all parameter sets used are relatively compatible with experimental data and the chiral effective field theory result. Moreover, the tensor couplings, Coulomb-exchange, $\ensuremath{\delta}$-meson, and isovector-isoscalar coupling terms play a significant role in predicting the canonical NS radius but not in the maximum mass of NS. For relatively large ${\ensuremath{\eta}}_{2\ensuremath{\rho}}$, the compatibility of the canonical NS radius predicted by the model with all of the observation results used in this work is better than that with the tensor couplings and Coulomb exchange excluded. Moreover, the presence of tensor couplings, Coulomb exchange, and various isovector-isoscalar nonlinear coupling terms influence the relation between NS tidal deformation and neutron skin thickness of $^{208}\mathrm{Pb}$. However, tensor couplings and Coulomb-exchange terms play a crucial role in making the NS tidal deformability prediction compatible with the constraints from observations and experimental data. In conclusion, tensor couplings and Coulomb-exchange RMF models have an essential role in finite nuclei predictions and implicitly influence the nuclear matter and NS property predictions.