Baryon–Baryon interaction effects on neutrino emission from direct URCA processes of baryons and modified URCA processes of nucleons in neutron star matter

Abstract

In the framework of the relativistic mean field theory, the neutrino emission from the baryonic direct URCA processes and nucleonic modified URCA processes in neutron star (NS) matter is investigated. We discuss particularly the influence of the extension of the SU(6) spin-flavor symmetry to the SU(3) flavor symmetry on the sizes of the neutrino energy losses, baryonic density and mass ranges of the above neutrino emission processes. In the nucleonic direct URCA processes, the neutrino energy losses in NS matter consisted of npe[Formula: see text] are observably higher than these in NS matter involving hyperons. For NS matter involving hyperons, the neutrino energy losses with the SU(3) flavor symmetry are slightly lower than those with the SU(6) spin-flavor symmetry. In the hyperonic direct URCA processes, the neutrino energy losses for the reactions of [Formula: see text] and [Formula: see text] with the SU(3) flavor symmetry are obviously smaller than these with the SU(6) spin-flavor symmetry. However, the neutrino energy loss of the reaction of [Formula: see text] with the SU(3) flavor symmetry is observably higher than that with the SU(6) spin-flavor symmetry. Moreover, the threshold densities of processes for [Formula: see text] with the SU(3) flavor and SU(6) spin-flavor symmetries are 0.868[Formula: see text]fm[Formula: see text] and 0.806[Formula: see text]fm[Formula: see text] (corresponding to 2.118[Formula: see text][Formula: see text] and 1.838[Formula: see text][Formula: see text]), respectively, which mean that it only happens in the interior of the massive NSs. For the neutron and proton branch modified URCA processes, the neutrino emission rates with the SU(3) flavor symmetry are also less than those with the SU(6) spin-flavor symmetry.