We have compared two RMF models for dense matter: one is the BB model in which cubic and quartic terms for the scalar field are included in the Lagrangian as nonlinear terms, and another is the ZM model in which the nonlinearity is contained in the connection between the effective nucleon mass and the scalar field. In this paper we have used the latter model to study the properties of asymmetric nuclear matter and the equation of state for supernova matter. We find that even though muons are included in the chemical composition of neutron-star matter, the ZM model still results in a small proton concentration so that only the modified Urca process occurs as a main neutrino reaction in neutron stars. This conclusion is opposite to that based on the BB model. This may provide an observational signature for the ZM model.
The incompressibility of dense matter based on the ZM model is consistent with both the experimental values extracted from the nuclear physics and the constraints placed on the EOS by observations of neutron star masses. If the EOS for supernova matter is described by the ZM model, the prompt mechanism for Type II supervovae cannot work. But this EOS is likely to be favourable to the delayed explosion mechanism because this model can lead to a large trapped lepton concentration at the core bounce and a large radius of the protoneutron star.
© European Southern Observatory (ESO) 1998
Online publication: January 16, 1998