Symmetry energy effect on hot nuclear matter and proto-neutron stars

Abstract

We examine the effects of symmetry energy on proto-neutron stars (PNSs) by employing equation of state (EOS) described by the relativistic mean-field (RMF) model. The thermal properties of dense matter and the bulk properties of PNSs are investigated under the assumptions of isothermy, isentropy, and fixed lepton fractions. The polytropic index is calculated at finite temperature, revealing a negative correlation with the PNS maximum mass that the EOS can support. The properties of PNSs during the heating and cooling stages along their evolution line are explored under different combinations of lepton fraction and entropy. We investigate the correlation between the symmetry energy slope $L$ and the properties of PNSs. As $L$ increases, the PNS radius also increases; however, this effect diminishes with a growing lepton fraction for the isentropic case. These results indicate that the nuclear symmetry energy and its density dependence play crucial roles in determining the properties of PNSs and their evolution stages.