Improved Quark Mass Density-dependent Model For Finite Nuclei And Strange Nuclei

There are four conventionally accepted fundamental interactions-gravitation,electro-magnetism,strong interaction,and weak interaction,where the strong interaction is the mechanism responsible for the strong nuclear force.In 1935,Yukawa published his theory of mesons,which explained the interaction between protons and neutrons.In 1947,the pions,which turned out to be examples of Yukawa’s proposed mesons,were found by the collaboration of Powell et al..The discovery of pions affirmed the concept of meson exchange picture.In 1970s,the relativistic mean-field theory(RMF),developed from the Yukawa’s meson exchange theory,was first proposed by Walecka.Up to now,the relativistic mean field theory has obtained considerable progress and achieved great success in describing the properties of finite nuclei,strange nuclei and nuclear matter.The RMF model based on baryon and meson degrees of freedom forms a good starting point for the study of nuclear system at low energy region.It is known that the nuclear system is mainly composed of quarks and gluons at sufficiently high temperature and high density.Therefore,a consistent nuclear theory describing the transition from nucleon and meson degrees of freedom to quarks and gluons is truly required to describe nuclei and nuclear matter over a wide range of density and tem-perature.Following this line of thought,several effective field theories based on the quark and meson degrees of freedom have been proposed.In 1988,Guichon developed the QMC model for nuclear matter,which describes nuclear matter as a collection of nonoverlapping MIT bags,scalar σ mesons and vector ω mesons.Subsequently,Toki with his collaborators constructed the so called quark mean field(QMF)model,where the nucleon is described in terms of the constituent quarks and their coupling with mesons and gluons.In 1981,Fowler,Raha and Weiner suggested the quark mass density dependent(QMDD)model to overcome the shortcoming of MIT bag model in the description on the quark deconfinement phase transition.Based on the QMDD model,an improved quark mass density dependent(IQMDD)model was developed by introducing quark and meson(σ,w and p)field coupling self-consistently.In this thesis,we mainly investigate the properties of finite nuclei and strange nuclei in terms of the IQMDD model.In order to investigate the properties of deformed nuclei,we develop the IQMDD code into a deformed version.By introducing the quark-omega tensor coupling,we refit a new parameter set called IQMDD2*,which is able to provide a reasonable description on finite nuclei.The original IQMDD parameter set was fitted to the saturation properties of nuclear matter,such as the symmetry energy,the incompressibility coefficient and the binding energy per nucleon at saturation density.It is fully necessary to test the validity and reliability of IQMDD parameters for describing the properties of finite nuclei.Actually,it is found that the spin-orbit splitting in finite nuclei given by IQMDD model is too small compared to the experimental values.In order to over-come this shortcoming,we have introduced a quark-omega tensor coupling term into the IQMDD model,which is proved to have an important influence on the spin-orbit splitting of nucleons.Then we refit the parameters to maintain the binding energies,charge radii and spin-orbit splitting of some typical spherical nuclei.For obtaining the reasonable neutron radius in heavy nuclei and softening the density dependence of the symmetry energy,we introduce the additional isoscalar-isovector coupling.This new resulting parameter set is referred to as IQMDD2*.It is shown that the IQMDD2*parameters is able to provide a good description not only for the ground-state properties of finite nuclei but also for the saturation properties of the nuclear matter.On the other hand,we investigate the properties of several deformed p-and sdshell A-hypernuclei in terms of the self-consistent relativistic mean field theory.With the experimental development,the strange nuclear physics has become a hot topic at present.As a sort of the strange nuclear system,the Λ hypernuclei is composed of one or more Λ hyperons and a nuclear core.Meanwhile,not affected by Pauli blocking from other nucleons,the K-mesons can be deeply embedded in a nucleus.This leads to the possible existence of deeply bound kaonic atoms or kaonic nuclei.The study of hypernuclei and K--nuclear system provides important information on the underlying YN interactions.Consequently this may lead to physical significance in dibaryon searching,SU(3)dynamics,relativistic ion collision as well as astrophysics.In chapter 3,the effect of tensor coupling on the Λ ground-state binding energy is discussed.After testing the validity of our models for describing the A single-particle energies of A-hypernuclei,we then investigate the hypernuclear deformation for the ground state of Si and S isotopes.For most of the Si and S isotopes,the deformation parameter is similar between the core nucleus and the corresponding hypernucleus,however,28Si and 32S make important exceptions.Utilizing the framework of relativistic mean field model,our calculation predicts formation of clusterlike structure in the ground state of 28Si and 32S,while the core nuclei in 29ΛSi and 33ΛS show a delocalized formation in the presence hyperon depending on the nuclear effective interaction.Then,in chapter 4,we evaluate the Λ superfluidity in β-stable strange hadronic matter at finite values of baryon density and temperature in the relativistic mean field(RMF)theory.It is well known that the ω-ρ cross interaction can produce large effect on the symmetry energy at high densities and the neutron skin thickness in heavy nuclei.Effects of the introduced isoscalar-isovector cross-interaction term on the Λ superfluidity are investigated systematically,by changing the isoscalar-isovector coupling term and pNN coupling term.It is found that the density region and the magnitude of the Λ pairing gap are dependent on the cross-interaction term.By solving the finitetemperature gap equation,we find that the obtained maximal critical temperature of Λsuperfluid is around 109 K.Finally,we investigate the properties of several possible light kaonic nuclei within the improved quark mass density-dependent model.The effect of the antikaon optical potential at saturation density on the properties of the kaonic nuclei is discussed.It is found that the antikaon optical potential has a sizable effect on the K-binding energy,decay width and K-density distribution in kaonic nuclei.The single K--nuclear states in the possible bubble nuclei are studied,with concentration on the experimentally accessible light nuclei.The calculations indicate that,when the K-meson is embedded in nuclei with speculated "bubble" structure,the depleted central nuclear density might be modified,and in certain cases,the bubble structure may even disappear.Equally important,the embedding K-meson can result in the growth of the pseudospin orbit splitting.