Study On Chiral Phase Transition Under OPT Method

Properties of hadronic matter at finite temperature and density is an important topic in particle physics,its fundamental theory is quantum chromodynamics(QCD),which is an important part of the particle physics standard model.With the further study of hadronic phase diagram,the influence of magnetic field and electric field background on phase diagram has attracted interest,and its practical significance is that strong magnetic field and electric field may be produced in the experiment of high energy heavy-ion collision.Since strong interaction is still difficult to handle in the non-perturbative region,effective models(e.g.,NJL models)have been an important auxiliary means to investigate strong interactions.Though they are not QCD,they have some important QCD features,and calculation is much easier,which makes them important tools for simulating QCD.It often needs appropriate calculation method when using effective model.An optimization perturbation theory(OPT)method is used in this paper.It is a variational method which takes into account some higher order perturbative effects by lower order perturbative calculation.In this thesis we use a NJL)2(SU model beyond the mean field approximation to investigate the chiral phase transition in the electric field background using OPT methods.we calculate the effective mass and condensation as a function of electric field and temperature,and use susceptibility to obtain a critical line of chiral phase transition in a TE-plane with a zero chemical potential.The results show that the electric field has the effect of promoting the restoration of chiral symmetry,the restoration of chiral symmetry of u quarks is faster than that of d quarks.The critical lines of chiral phase transition from different susceptibilities are different,and the difference is obvious in the central part of the critical line in electric field-temperature plane.