The Effects Of Nucleon-nucleon Short-range Correlations On Neutron Stars

Because of the short-range components of nucleon-nucleon interaction,nucleons in nuclear ground states can form short-range correlated pairs with large relative mo-mentum and small center-of-mass momentum.Nuclear scatting experiments show that even in neutron-rich nuclei like²⁰⁸Pb neutron-proton correlated pair is the dominate correlated pair,which means that the fraction of correlated protons is greater than neu-trons’in neutron-rich nuclei.Neutron star matter is classical neutron-rich matter with high density,so it is essential to count nucleon-nucleon short-range correlations in the study of neutron stars.In the study of neutron stars with relativistic mean field model,nucleon-nucleon short-range correlations are neglected in form.Nucleon-nucleon short-range corre-lations can be phenomenologically introduced through the correlation induced high momentum distribution of nucleons.In the traditional relativistic mean field model,the nucleon’s scalar density operatorˉΨ_NΨ_N,nucleon’s currentˉΨ_Nγ^νΨ_N,nucleon’s isospin currentˉΨ_Nγ^νt_NΨ_Nare replaced by their expectation values of ground state|Φ?,where all the nucleons are below the Fermi surface.In order to introduce the nucleon-nucleon short-range correlations in relativistic mean field model,we use a new ground state|Φ_SRC?that includes nucleon-nucleon short-range correlations,i.e.,the momentum distribution of nucleons in the new ground state has high-momentum components.After introducing the nucleon-nucleon short-range correlations,the equation of s-tate of the traditional neutron star becomes softer so that the calculated maximum mass becomes smaller but still reaches the mass of the largest neutron star J0740+6620 ever observed.The equation of state of the Hyperon star changes differently under different densities,and the calculated maximum mass becomes larger,but it still cannot reach the mass of J0740+6620.The particle fractions change dramatically for both the tradition-al neutron star and the hyperon star after introducing the nucleon-nucleon short-range correlations.Apart from this,the numerical calculation shows that the maximum prob-ability for nucleons in the neutron star to form short-range correlated pairs is above40%,which is because of the high isospin asymmetryδ=（ρ_n-ρ_p）/（ρ_n+ρ_p）in neu-tron stars.It’s worth noting that the mass-radius relations of the traditional neutron star and the hyperon star can satisfy the stringent limits provided by the gravitational wave observation of LIGO-Virgo,only after introducing the nucleon-nucleon short-range correlations.Therefore,nucleon-nucleon short-range correlations can’t be neglected in the study of neutron stars.By comparing the probabilities of correlation between different densities of neutron stars,we found that the central part of the neutron star is more affected.The effects of effective nucleon mass and compression modulus at saturated nuclear matter on the masses of traditional neutron stars and hyperon stars are also studied in this work.Hyperon stars can hardly reach the mass of observed neutron star J0740+6620 when we vary effective nucleon mass and compression modulus,even after introducing the nucleon-nucleon short-range correlations.