Effects of the ϕ Meson on the Properties of Hyperon Stars in the Density-dependent Relativistic Mean Field Model

The effects of the ϕ meson on the properties of hyperon stars are studied systematically in the framework of the density-dependent relativistic mean field (DDRMF) model. The ϕ meson shifts the hyperon threshold to a higher density and reduces the hyperon fractions in neutron star cores. It also strongly stiffens the equation of state calculated with various DDRMF effective interactions and increases the maximum mass of hyperon stars, but only a few effective interactions survive under the constraints from recent astrophysical observations. In the DDRMF model, the conformal limit of the sound velocity is still in strong tension with the fact that the maximum mass of neutron stars obtained in theoretical calculations reaches about 2 M ⊙. Based on different interior composition assumptions, we discuss the possibility of the secondary object of GW190814 as a neutron star. When the ϕ meson is considered, DD-ME2 and DD-MEX support the possibility that the secondary object of GW190814 is a hyperon star rapidly rotating with Kepler frequency.