Impact of Neutrino Trapping on the Equation of State and Structure of Hybrid Stars with 2SC Quark Matter

Abstract

We investigate how sensitive the effects of neutrino trapping on hot hybrid stars are to uncertainties in the hadronic and quark equations of state and in the thermodynamic construction of the hadron--quark transition. The hadronic phase is described by finite-temperature covariant density functional equations of state, and the quark phase by a three-flavor Nambu--Jona-Lasinio (NJL) model with repulsive vector interactions and two-flavor color superconductivity. Because confinement is absent from the NJL model, an effective pressure shift $B^*$ is used phenomenologically to locate the deconfinement transition. We construct isentropic stellar equations of state with and without trapped electron neutrinos, vary the quark vector coupling and the nuclear symmetry-energy slope, and compare global with local conservation of electron-lepton number within phase coexistence. Neutrino trapping generically shifts deconfinement toward higher density throughout the parameter range considered. Increasing the vector interaction stiffens quark matter and raises the maximum stellar mass, but only moderately for the couplings studied. We also examine stronger diquark pairing and RG-consistent regularization, instead of sharp momentum cut-off: both affect the pairing gap, phase boundaries, and quark-core composition more strongly than they alter the qualitative trends of the stellar mass--radius sequences. Conversely, trapping reduces the sensitivity to the hadronic symmetry-energy slope because the enhanced proton fraction drives matter toward greater isospin symmetry. Global and local lepton-number prescriptions produce rather similar mass--radius relations but substantially different internal phase structures: global conservation leads to a considerably more extended mixed phase.