NJL Model Study On Phase Transition Of Strongly Interacting Matter At Finite Temperature And Density

Quantum Chromodynamics(QCD)is a fundamental theory of strong interaction.There are two nonperturbative properties of QCD in the low energy region: color confinement and dynamical chiral symmetry breaking,which lead to very rich phase structure of QCD in the low energy region.Under extreme conditions such as high temperature and high density,chiral phase transition and superfluid phenomena may occur in strong interaction matter.In this paper,the effective theory–NJL model is used to describe the strong interaction system and the self-consistent mean field approximation method is briefly introduced.The background and significance of the research are given.Then,in Chapter 3,we get the gap equation at finite isospin chemical potential in the self-consistent mean field approximation,and further obtain the corresponding expressions of thermodynamic potential and condensation.In the self-consistent mean field approximation,it is necessary to introduce a parameter ? which indicates the contribution weight of the exchange interaction term(it plays a very important role in the study of finite density systems),and it can be determined by experiments.However,currently due to the lack of reliable experimental data we can consider ? as a free parameter.After that,we calculated the corresponding energy density and isospin density,and compared them with the lattice results.We found that when ? = 0.5,the obtained results are in good agreement with the lattice results,which means that the role of the exchange term should be considered in the systems with finite isospin chemical potential.Finally,we calculate some thermodynamic quantities and phase diagrams with the finite isospin chemical potential,and compare different contribution weights of exchange terms on them.In Chapter 4,we further get the gap equations at finite isospin and baryon chemical potentials within the self-consistent mean field approximation,and obtain the thermodynamic potential and condensation.After that,we study the phase transition properties of the system at finite isospin and baryon chemical potentials,and discuss the influence of different contribution weights of the exchange term.The CEP(critical endpoint)and TCP(tricritical point)of the phase structure with different ? values are given.The critical baryon chemical potential and critical temperature of the phase transition are also calculated.