Chiral Phase Transition Of The NJL Model Under A Constant Electric Field

The investigation on QCD matter is an attractive topic in particle physics.Most researches focus on the effects of high temperature or high density,some researches focus on the effects of magnetic fields.On the other hand,both Au+Au and Pb+Pb heavyion collisions produced strong electric fields of the same order of magnitude as magnetic fields.Therefore investigation on the effects of electric fields becomes important.Quantum Chromodynamics(QCD)is the fundamental theory of the strong interaction.Although its enormous success in high energy region,the applicability of QCD in nuclear interactions or hadronic processes at low energies is still limited.The difficulties are largely technical,associated with the non-perturbative features of the theory.An alternative path out of this limit is using effective models which incorporate features compatible with the low energy QCD.NJL(Nambu Jona-Lasinio)model is such a model.It has chiral symmetry in chiral limit and this symmtry breaks spontaneously leading to massless Goldstone bosons.It can be used to study quark matter,hadrons,and the chiral phase transition at finite temperature as well as zero temperature.Due to infrared divergences and close to the critical points,Quantum field theory at finite temperature faces a major complication,the breakdown of perturbation theory,nonperturbative methods are required in general.Besides other methods,the optimized perturbation theory(OPT)was proposed to describe the thermodynamics.It is based on a reorganization of the interacting Lagrangian such that it depends on an arbitrary(mass)parameter,to be fixed by a definite optimization prescription.In this thesis,we investigate the effects of electric fields on chiral phase transition at finite temperature and chemical potential.A two-flavor NJL model beyond the mean field approximation is used with OPT method,we expand the effective potential perturbatively to the first order.The results show that(1)electric field can weaken the constituent dynamical quark masses so that it enhances the chiral symmetry restoration,(2)when the temperature grows the critical electric field decreases and(3)the chemical potential tends to partially restore the chiral symmetry and leads to the lowering of the critical electric field.