Hyperon stars in a modified quark meson coupling model

We determine the equation of state (EOS) of nuclear matter with the inclusion of hyperons in a self-consistent manner by using a modified quark meson coupling model where the confining interaction for quarks inside a baryon is represented by a phenomenological average potential in an equally mixed scalar-vector harmonic form. The hadron-hadron interaction in nuclear matter is then realized by introducing additional quark couplings to $\sigma ,\omega$, and $\rho$ mesons through mean-field approximations. The effect of a nonlinear $\omega \text{−}\rho$ term on the EOS is studied. The hyperon couplings are fixed from the optical potential values and the mass-radius curve is determined satisfying the maximum mass constraint of $2{\mathrm{M}}_{\odot }$ for neutron stars, as determined in recent measurements of the pulsar PSR J0348+0432. We also observe that there is no significant advantage of introducing the nonlinear $\omega \text{−}\rho$ term in the context of obtaining the star mass constraint in the present set of parametrizations.

Figure 1

The pressure at various densities for nuclear matter (NM) and hyperon matter (HM).

Figure 2

Effective mass of baryon at quark mass $m_q=150$ MeV.

Figure 3

Hyperon $(\mathrm{\Lambda },\mathrm{\Sigma },\mathrm{\Xi })$ potentials as a function of density.

Figure 4

The EOS at various cascade potentials and different values of ${\mathrm{\Lambda }}_{\nu }$ for quark mass $m_q=150$ MeV. The shaded region shows the empirical EOS obtained by Steiner et al. from a heterogeneous set of seven neutron stars.

Figure 5

Particle fraction at different cascade potentials of (a) $U_{\mathrm{\Xi }}=-18$ MeV, (b) $U_{\mathrm{\Xi }}=-10$ MeV, and (c) $U_{\mathrm{\Xi }}=0$ MeV for the quark mass $m_q=150$ MeV.

Figure 6

Strangeness fraction and particle fraction variation with density. The upper grid is for neutron and the lower one represents ${\mathrm{\Xi }}^{-}$ hyperon.

Figure 7

Strangeness fraction as a function of density for various cascade potentials.

Figure 8

Star mass as a function of radius for various values of the coupling parameter and cascade potential at quark masses (a) $m_q=80$ MeV and (b) $m_q=150$ MeV. Also shown is the mass observed for the pulsar PSR J0348+0432 in [25].