New Hyperon Equations of State for Supernovae and Neutron Stars in Density-dependent Hadron Field Theory

Abstract

We develop new hyperon equation of state (EoS) tables for core-collapse supernova simulations and neutron stars. These EoS tables are based on a density-dependent relativistic hadron field theory where baryon-baryon interaction is mediated by mesons, using the parameter set DD2 from Typel et al. (2010) for nucleons. Furthermore, light and heavy nuclei along with the interacting nucleons are treated in the nuclear statistical equilibrium model of Hempel and Schaffner-Bielich which includes excluded volume effects. Of all possible hyperons, we consider only the contribution of $Λ$s. We have developed two variants of hyperonic EoS tables: in the np$Λϕ$ case the repulsive hyperon-hyperon interaction mediated by the strange $ϕ$ meson is taken into account, and in the np$Λ$ case it is not. The EoS tables for the two cases encompass wide range of density ($10^{-12}$ to $\sim$ 1 fm$^{-3}$), temperature (0.1 to 158.48 MeV), and proton fraction (0.01 to 0.60). The effects of $Λ$ hyperons on thermodynamic quantities such as free energy per baryon, pressure, or entropy per baryon are investigated and found to be significant at high densities. The cold, $β$-equilibrated EoS (with the crust included self-consistently) results in a 2.1 M$_{\odot}$ maximum mass neutron star for the np$Λϕ$ case, whereas that for the np$Λ$ case is 1.95 M$_{\odot}$. The np$Λϕ$ EoS represents the first supernova EoS table involving hyperons that is directly compatible with the recently measured 2 M$_{\odot}$ neutron stars.