Lepton effects on the proto-neutron stars with the hadron-quark mixed phase in the Nambu-Jona-Lasinio model

TL;DR

This study investigates how leptons influence the structure of hybrid stars with a hadron-quark mixed phase using the NJL model, revealing that lepton fraction significantly affects star stability and maximum mass.

Contribution

It introduces a detailed analysis of lepton effects on hybrid star structures with different phase transition constructions using the NJL model and nuclear EOS.

Findings

Pure quark phases do not appear in stable star cores.

Maximum star masses increase by about 10% with phase transition at high lepton fractions.

Lepton fraction impacts star stability more than temperature in the NJL model.

Abstract

We study the structures of hybrid stars with leptons at finite temperature under beta equilibrium. For the quark phase, we use the three flavor Nambu-Jona-Lasinio (NJL) model. For the hadron phase, we adopt nuclear equation of state (EOS) by Shen et al.. This EOS is in the framework of the relativistic mean field theory including the tree body effects. For the hadron-quark phase transition, we impose the bulk Gibbs construction or the Maxwell construction to take into account uncertainties by {\it finite size effects}. We find that the pure quark phase does not appear in stable star cores in all cases. With the phase transition, the maximum masses increase $\sim 10 %$ for high lepton fraction. On the contrary, without the transition, they decrease $\sim 10 %$. We also find that, in the NJL model, the lepton fraction is more important for structures of unstable stars than the temperature. This result is important for many astrophysical phenomena such as the core collapse of massive stars.