Chiral Phase Transition Under Constant Electric Field

Quantum chromodynamics(QCD)is the fundamental theory to describe the hadronic matter and their dynamics,hadronic matter at zero and finite temperatures have been extensively studied.One of the important content is to study its phase diagram.Phase diagrams are not only the key to understanding natural phenomena such as dense stars and the early universe,but also the key to understanding laboratory experiments such as relativistic heavy-ion collisions.In high energy heavy ion collision experiments,quark-gluon plasma can be produced,which lay an experimental foundation for further understanding the properties of strong interaction.In recent years,the phase transition of hadronic matter under the magnetic background has become a hot topic.Because not only magnetic field but also electric field will be produced in the non-central high energy heavy-ion collisions,it is of great practical significance to study the influence of electric field on phase transition.Although much theoretical work has been done on QCD phase diagrams,we has known little about it as yet.One of the main reasons is that the energy range involved requires non-perturbative calculations QCD and is thus far not feasible.The lattice QCD method which is based on the first principle is also difficult to deal with the density region because of the symbol problem.Therefore,most of the knowledge about QCD phase diagrams comes from effective models,such as the Nambu-Jona-Lasinio(NJL)model,the Polyakov-Nambu-Jona-Lasinio(PNJL)model,the quark meson model and so on.Susceptibility is an important physical quantity in investigating phase transition,which is of great significance for determining critical end point and phase diagrams.One can obtain the properties of phase transition by the continuity of susceptibility.According to the discontinuity point(or peak value),the phase transition can be judged as a first order phase transition,a second order phase transition or a crossover.In this thesis SU(3)NJL model is used to investigate the chiral phase transition in the electric field background.We calculate the effective mass of quarks as a function of electric field and temperature,and determine the phase diagram of the chiral phase transition in the electric field-temperature plane at zero chemical potential using thermal susceptibility,chiral susceptibility,etc.The results show that the electric field can accelerate the restoration of chiral symmetry,the restoration of chiral symmetry of u quarks is faster than that of d quarks.The critical line of chiral phase transition determined by different magnetic susceptibility is different,the difference is obvious in the central part of the critical line in electric field-temperature plane.