Transport Coefficients of Hyperonic Neutron Star Cores

Abstract

We consider transport properties of the hypernuclear matter in neutron star cores. In particular, we calculate the thermal conductivity, the shear viscosity, and the momentum transfer rates for npΣ−Λeμ composition of dense matter in β–equilibrium for baryon number densities in the range 0.1–1 fm−3. The calculations are based on baryon interactions treated within the framework of the non-relativistic Brueckner-Hartree-Fock theory. Bare nucleon-nucleon (NN) interactions are described by the Argonne v18 phenomenological potential supplemented with the Urbana IX three-nucleon force. Nucleon-hyperon (NY) and hyperon-hyperon (YY) interactions are based on the NSC97e and NSC97a models of the Nijmegen group. We find that the baryon contribution to transport coefficients is dominated by the neutron one as in the case of neutron star cores containing only nucleons. In particular, we find that neutrons dominate the total thermal conductivity over the whole range of densities explored and that, due to the onset of Σ− which leads to the deleptonization of the neutron star core, they dominate also the shear viscosity in the high density region, in contrast with the pure nucleonic case where the lepton contribution is always the dominant one.

Transport coefficients of magnetized neutron star cores

“…Transport coefficients for the hypernuclear NS cores can be in principle, calculated using the similar formalism as studied here. For the nonmagnetized case this was done by [100] for two models of hypernuclear interaction. The momentum transfer rates within the free-particle model and npeΣ − composition were considered in [9].…”

“…When collisions of charged baryons are considered, in principle the interference between the electromagnetic and strong interaction channels needs to be taken into account [98]. However, it was found that the charged baryons usually give negligible contribution to the transport coefficients [83,99,89,100]. Therefore, we neglect the interference contribution and consider the electromagnetic and strong channels separately for simplicity.…”

“…Effective interaction construction on a basis of the variational methods and subsequent application to NS matter was performed in [111,112,113]. The calculations within the Brueckner-Hartree-Fock (BHF) theory [114] were also carried out [111,115,99,116,89,100]. Frequently a partial wave expansion of the scattering problem is used and we show how this expansion enters the calculations in sec.…”

Hyperons in Neutron Stars

“…Now, a final remark about the transport coefficients of hyperonic matter. In this sector, few calculations have been completed [267]. These calculations are relevant for the very important application in astrophysical systems, like BNSM and SNe.…”

“…A microscopic study of thermal conductivity and shear viscosity of hyperonic matter have been very recently proposed in Ref. [267], in the framework of BHF approaches using versions a and e of the NSC97 NY and YY interactions. The effect of hyperonic three-body forces was not included.…”