Analysis Of Nuclear Tensor-Force Effects In Covariant Density Functional Theory

The nuclear tensor force is one of the most important components of the nucleon-nucleon interaction.In the framework of covariant density functional theory(CDFT),the tensor force is,however,mixed together with the other components.Thus,it is infeasible to compare the tensor-force effects in relativistic framework with those in nonrelativistic framework in a fair and direct way.Aiming at this problem,for the first time,we have realized a quantitative extraction and analysis of the tensor force in covariant density functional theory,making it possible to perform a fair and direct comparison between the tensor-force effects in relativistic and nonrelativistic framework.Based on the relativistic Hartree-Fock(RHF)theory and the newly developed formulas to extract the tensor force,we have investigated the tensor-force effects in the single-particle shell evolution and on the spin-orbital splitting of the neutron drops,as well as the tensor-force effects on the spin-isospin excitations.Meanwhile,the strength of the tensor force in the effective interaction is explored.By performing the nonrelativistic reduction of the relativistic two-body interactions,the tensor force component in each meson-nucleon coupling is identified.With the RHF effective interaction PKA1,the evolution of the magic shell in Z,N = 8,20,and 28 isotopes and isotones is investigated.It is found that the tensor force plays a significant role in the evolution.In addition,compared with the nonrelaticistic effective interactions Skyrme SLy5wT and Gogny GT2,the tensor force in PKA1 is found to be too weak.The evolution of energy gap between the proton states 1h11/2 and 197/2 in Sn isotopes along with the neutron number and that between the neutron states 1i13/2 and 1h9/2 in N = 82 isotones along with the proton number are investigated.It is shown that tensor force plays a critical role in reproducing the experimental trend,and tensor contribution mainly comes from the 7r pseudo-vector coupling.The strength of the tensor force is also investigated.It is found that enhancing the strength of ? pseudo-vector coupling,especially weakening its density dependence,will improve the description of the shell evolution above.This conclusion provides,to some extend,a quantitative support for the argument known as "tensor renormalization persistency".Taking the results of relativistic Brueckner-Hartree-Fock(RBHF)calculation starting from realistic nuclear force as "meta-data",the evolution of the spin-orbit splitting with neutron number in the neutron drop is studied.Since the RBHF calculation doesn't involve any beyond-mean-field effects,it allows a fair and direct comparison with the RHF calculation within absolute mean-field level.The critical role of the exchange term of the it meson is certified,and it is the tensor force arising from it that dominates.Treating the slope between the splitting of neighbouring closed(sub)shells with equal weight,it is found that when the strength of ? pseudo vector coupling,f?,is enhanced by a factor of 1.4 or the density dependence coefficient a? is reduced to 0.3 times its original value,the RHF calculation with PKO1 reproduces the meta-data best.Also,reducing the density dependence is shown to be more efficient,to some extent.This reflects the property of "tensor renormalization persistency" again.Finally,the random phase approximation(RPA)based on the relativistic Hartree-Fock theory is extended so as to perform fully self-consistent calculation with the ? me-son tensor coupling involved.Within the newly developed framework,the properties of Gamow-Teller resonance and spin-dipole resonance are investigated.Moreover,for the first time,the tensor-force effects on the spin-isospin excitations are explored in the framework of covariant density functional theory.It is found that,with the current RHF effective interactions,the tensor force influences the Gamow-Teller resonance main-ly through the mean field indirectly.In contrast,it influences the spin-dipole resonance directly through the RPA residual interactions.Iffff is enhanced by a factor of 1.4 or a? is reduced to 0.3 times its original value,the tensor force still influences the Gamow-Teller resonance mainly through the mean field indirectly,while it influences the spin-dipole resonance through both the mean field and the residual interaction in this case.