Direct URCA Process With The Hyperon-Hyperon Interactions

The study on the properties of cooling of neutron star is an important way toexplore the internal phase structure of neutron stars and is a frontier issue in the fieldof nuclear astrophysics. This paper has described hyperon- hyperon interaction in theframework of the relativistic mean field theory (RMFT) including additional scalarmeson ? *and vector meson ? field and has performed direct URCA process ofnucleon and hyperon in neutron star matter. Neutron star cooling process depends onthe most powerful cooling process among all cooling mechanisms, moreover, thedirect URCA process of nucleon and the direct URCA process of hyperon are bothbelong to enhanced cooling process. So, study these cooling process in depth hasimportant signification for the understanding of the neutron star cooling process andthecloselyrelatedphasestructureofneutronstars.Previous research carried out in this area mainly in the non-relativisticapproximation. However, direct URCAprocess occurs in the several density areas ofnormal nuclear matter, in this density range, the particle motion is necessarilyrelativistic.In this paper, with the framework of relativistic mean field theory, the particlesnumber of nucleon and hyperon, effective mass and other physical quantities aregiven through the self-consistent solution. Furthermore, these physical quantities areused as input through the weak relativistic matrix elements in relativistic manner, theneutrino energy loss caused by the direct URCA processes including nucleon andhyperon is calculated. The results show that the total neutrino emissivitybythe directURCA processes including nucleon and hyperon decrease with the increase ofhyperon number densities. The decreasing of emissivitywas caused bythe increasingofbaryondensityandthedecreasingofeffectivemassofnucleonandhyperon Hyperon- hyperon interaction used in this article is weak hyperon- hyperoninteraction, which is consistent with the new experimental results ?? hyperoninteraction ?B ? ?? 1MeV(the so-called Nagara events). In order to comparison, thepaper also gives calculation results with the strong hyperon - hyperon interactions(△BAA≈5MeV) and with noσ*andσmesons included. The results showed thatonly the weak hyperon- hyperon interaction can make the(?)reactionprocessoccurringintheneutronstar.This paper also calculated the neutrino emissivity with non-relativisticapproximation.Theresultsshowthattheneutrino emissivitydecreasewiththebaryonnumber density increase. However, compared with the relativity, it decreses muchsmaller.Sotheresultsofrelativityarereliable.