  An improvement in the treatment of the isovector channel of relativistic mean
field (RMF) models based on effective field theory (E-RMF) is suggested, by
adding an isovector scalar (delta) meson and using a similar procedure to the
one used by Horowitz and Piekarewicz to adjust the isovector-vector channel in
order to achieve a softer density dependent symmetry energy of the nuclear
matter at high density. Their effects on the equation of state (EOS) at high
density and on the neutrino mean free path (NMFP) in neutron stars are
discussed.
