Implications of isoscalar and isovector scalar meson mixed interaction on nuclear and neutron star properties

The properties of finite nuclei, bulk nuclear matter, and neutron stars are studied using the relativistic mean field model which includes nonlinear couplings between isoscalar and isovector mesons. The quartic interaction ${\sigma }^2{\delta }^2$ due to isoscalar and isovector scalar, $\sigma$ and $\delta$ mesons, is also taken into account in addition to vector meson mixing ${\omega }^2{\rho }^2$. Several HPNL sets (named from Himachal Pradesh University Nuclear Laboratory) are generated to assess the influence of isoscalar and isovector scalar meson mixed interactions ${\sigma }^2{\delta }^2$ on the density dependence of symmetry energy and neutron star properties. These parametrizations correspond to different values of coupling constant, ${\mathrm{\Lambda }}_{\sigma \delta }$ of $\sigma -\delta$ meson mixing and are obtained by fitting the available experimental data of ground state properties (binding energies and charge radii) for finite nuclei, infinite nuclear matter, and observed maximum mass of PSR $\text{J}0740+6620$ by following the ${\chi }^2$ minimization procedure. Furthermore, the $\sigma -\delta$ mixing is found to have a large influence on the radius and tidal deformability of a canonical neutron star. These new relativistic interactions are found to be simultaneously compatible with the constraints on the equation of state of symmetric nuclear and pure neutron matter from particle flow data in heavy ion collisions, the neutron skin thickness of ${}^{208}\mathrm{Pb}$ from PREX-II results, the mass-radius relations measured from NICER, and the limits of dimensionless tidal deformability of a canonical neutron star from binary neutron star merger GW170817 and GW190814 events.

Figure 1

Variation of pressure as a function of baryon density for symmetric nuclear matter (SNM) computed with HPNL's parametrizations. The shaded region represents the experimental data taken from Refs. [13, 45].

Figure 2

Variation of pressure as a function of baryon density for pure neutron matter (PNM) computed with HPNL's parametrizations. The shaded region represents the experimental data taken from Ref. [13].

Figure 3

Symmetry energy coefficient ($J$) as a function of baryon density scaled to saturation density for various HPNL parametrizations. The constraints on the magnitude of the symmetry energy coefficient at $J\left(2{\rho }_0\right)$: $J\left(2{\rho }_0\right)=62.8\pm 15.9$ MeV [46], $J\left(2{\rho }_0\right)=51\pm 13$ MeV from nine analyses of neutron star observables since GW170817 [47] and J($2{\rho }_0$) = $40.2\pm 12.8$ MeV based on microscopic calculations with various energy density functionals [48] are also shown.

Figure 4

Variation of density dependence of symmetry energy (L) as a function of baryon density scaled to saturation density for various HPNL parametrizations considered in the present work.

Figure 5

Variation of third order coefficient of symmetry energy, $Q_{\mathrm{sym}}$, with coupling parameters ${\mathrm{\Lambda }}_{\sigma \delta }$.

Figure 6

Speed of sound squared as a function of scaled baryon density $\rho /{\rho }_0$ in units of speed of light squared. The horizontal dashed line represents the conformal limit given by $c_s^2=1/3$ [61].

Figure 7

Mass radius relationship of neutron star for various HPNL parametrizations. The shaded regions labeled with NICER representing the mass-radius constraints from NICER observations [3, 4] are also shown.

Figure 8

Plot representing the dependence of radius $R_{1.4}$ on coupling ${\mathrm{\Lambda }}_{\sigma \delta }$.

Figure 9

Correlation between neutron skin thickness $\mathrm{\Delta }{r}_{np}$ and radius $R_{1.4}$. The shaded regions depict the neutron skin thickness of ${}^{208}\mathrm{Pb}\mathrm{\Delta }{r}_{np}$=$0.283\pm 0.071$ fm from PREX-II [10], $\mathrm{\Delta }{r}_{np}=0.19\pm 0.02$ fm) from Reinhard et al. [15] and $\mathrm{\Delta }{r}_{np}$ for ${}^{48}\mathrm{Ca}$ ($\mathrm{\Delta }{r}_{np}=0.14$–0.20 fm) at RCNP [50].

Figure 10

(a) Correlations between the slope of symmetry energy $L$ and radius $R_{1.4}$. (b) Correlation between ${\mathrm{\Lambda }}_{1.4}$ and $R_{1.4}$. The constraints on ${\mathrm{\Lambda }}_{1.4}$ from GW170817(${\mathrm{\Lambda }}_{1.4}={190}_{-120}^{+390})$ [6] and GW190814 (${\mathrm{\Lambda }}_{1.4}={616}_{-158}^{+273})$ [28] are also displayed.

Figure 11

Variation of dimensionless tidal deformability ($\mathrm{\Lambda }$) with respect to gravitational mass of neutron star for various HPNL parametrizations.