New relativistic effective interaction for finite nuclei, infinite nuclear matter, and neutron stars

We carry out the study of finite nuclei, infinite nuclear matter, and neutron star properties with the newly developed relativistic force, the Institute of Physics Bhubaneswar-I (IOPB-I). Using this force, we calculate the binding energies, charge radii, and neutron-skin thickness for some selected nuclei. From the ground-state properties of superheavy nuclei ($Z=120$), it is noticed that considerable shell gaps appear at neutron numbers $N=172$, 184, and 198, manifesting the magicity at these numbers. The low-density behavior of the equation of state for pure neutron matter is compatible with other microscopic models. Along with the nuclear symmetry energy, its slope and curvature parameters at the saturation density are consistent with those extracted from various experimental data. We calculate the neutron star properties with the equation of state composed of nucleons and leptons in $\beta$-equilibrium, which are in good agreement with the x-ray observations by Steiner [Astrophys. J. 722, 33 (2010)] and Nättilä [Astron. Astrophys. 591, A25 (2016)]. Based on the recent observation of GW170817 with a quasi-universal relation, Rezzolla et al. [Astrophys. J. Lett. 852, L25 (2018)] have set a limit for the maximum mass that can be supported against gravity by a nonrotating neutron star in the range $2.01\pm 0.04\lesssim M\left(M_{\odot }\right)\lesssim 2.16\pm 0.03$. We find that the maximum mass of the neutron star for the IOPB-I parametrization is $2.15M_{\odot }$. The radius and tidal deformability of a canonical neutron star of mass $1.4M_{\odot }$ are 13.2 km and $3.9\times {10}^{36}\mathrm{g}{\mathrm{cm}}^2{\mathrm{s}}^2$, respectively.

Figure 1

The neutron-skin thickness as a function of the asymmetry parameter. Results obtained with the parameter set IOPB-I are compared with those of the sets NL3 [13], FSUGarnet [67], G3 [21], and experimental values [76]. The shaded region is calculated using Eq. (39).

Figure 2

The two-neutron separation energy as a function of neutron number for the isotopic series of Ca, Ni, Zr, Sn, and Pb nuclei with NL3 [13], FSUGarnet [67], G3 [21], FRDM [80], and experimental data [68] whenever available. The dotted circle represents the magicity of the nuclei.

Figure 3

Density-dependent symmetry energy from Eq. (32) with different E-RMF parameter sets along with IOPB-I parametrization. The shaded region is the symmetry energy from IAS [92], HIC Sn+Sn [93], and ASY-EoS experimental data [94]. The zoomed pattern of the symmetry energy at low densities is shown in the inset.

Figure 4

The energy per neutron as a function of neutron density with NL3 [13], FSUGarnet [67], G3 [21], and IOPB-I parameter sets. Other curves and shaded regions represent the results for various microscopic approaches such as Baldo-Maieron [95], Friedman [96], auxiliary-field diffusion Monte Carlo [97], Dutra [53], Gezerlis [98], and Hebeler [99] methods.

Figure 5

Pressure as a function of baryon density for the IOPB-I force. The results with NL3 [13], FSUGarnet [67], and G3 [21], are compared with the EoS extracted from the analysis [101] for the (a) symmetric nuclear matter (SNM) and (b) pure neutron matter (PNM).

Figure 6

The equations of statewith NL3, FSUGarnet, G3, and IOPB-I sets for nuclear matter under charge neutrality as well as the $\beta$-equilibrium condition. The shaded region (violet) represents the observational constraint at $r_{ph}=R$ with uncertainty of $2\sigma$ [104]. Here, $R$ and $r_{ph}$ are the neutron star radius and the photospheric radius, respectively. The other shaded region (red and orange) represents the QMC+Model A equation of state of cold dense matter with $95\%$ confidence limit [103]. The region zoomed near the origin is shown in the inset.

Figure 7

The mass-radius profile predicted by NL3, FSUGarnet, G3, and IOPB-I parameter sets. The recent observational constraints on neutron-star masses [107, 108] and radii [103, 104, 116, 117] are also shown.

Figure 8

The tidal deformability $\lambda$ as a function of neutron star mass with different EoS.

Figure 9

Different values of $\mathrm{\Lambda }$ generated by using IOPB-I along with NL3, FSUGarnet, and G3 EoS are compared with the $90\%$ and $50\%$ probability contour in the case of low spin, $\left|\chi \right|\le 0.05$, as given in Fig. 5 of GW170817 [27].