Supersoft Symmetry Energy Encountering Non-Newtonian Gravity in Neutron Stars

Considering the non-Newtonian gravity proposed in grand unification theories, we show that the stability and observed global properties of neutron stars cannot rule out the supersoft nuclear symmetry energies at suprasaturation densities. The degree of possible violation of the inverse-square law of gravity in neutron stars is estimated using an equation of state of neutron-rich nuclear matter consistent with the available terrestrial laboratory data.

Figure 1

The inset shows two typical examples (MDIx0 and MDIx1) of the density dependence of the nuclear symmetry energy. The MDIx1 (MDIx0) EOS with (without) the Yukawa contribution using different values of the $g^2/{\mu }^2$ in units of ${\mathrm{GeV}}^{-2}$ are shown.

Figure 2

The mass-radius relation of static neutron stars with the MDIx1 (MDIx0) EOS with (without) the Yukawa contribution. The static neutron star sequences constrained by the rotational frequency 716 Hz of the J1748-2446ad [58] are taken from Haensel et al. [57]. The numbers above the lines are the $g^2/{\mu }^2$ values in units of ${\mathrm{GeV}}^{-2}$.

Figure 3

The momenta of inertia of neutron stars with the MDIx1 (MDIx0) $E_{\mathrm{sym}}(\rho )$ with (without) the Yukawa contribution. The numbers above the lines are the $g^2/{\mu }^2$ values in units of ${\mathrm{GeV}}^{-2}$.