Researching Roberge-Weiss Phase Pransition In Ultrastrong Magnetic Field

The study of QCD phase transition in strong magnetic field can deepen our understanding of the early evolution of the universe,the inner structure of compact stars and noncentral heavy-ion collisions.Roberge and Weiss(RW)found that the partition function of SU(N)gauge theory with imaginary chemical potential ?=i?/?,is a periodic function of ? and a first order phase transition appear at ?=(2k+1)?/N for high temperature.The study of RW transition is helpful to understand the QCD deconfinement phase transition at finite density.It is well known that strong magnetic field can lead to the low temperature magnetic catalysis and high temperature inverse magnetic catalysis of quark condensation.However,it is not clear how strong magnetic field affect the properties of RW transition endpoint.In this study,we adopt the Polyakov extended Nambu-Jona-Lasinio model(PNJL)to investigate the RW transition in strong magnetic field.We calculate the Polyakov loop and quark condensation by using the traditional fixed coupling parameter and the improved coupling parameter varying with the magnetic field,respectively.In the first case,we find that both the critical temperatures of the deconfinement phase transition and the RW transition endpoint increase with the increase of the magnetic field,which is similar to the magnetic catalytic effect of quark condensation.We confirmed that the endpoint of RW transition maintains second-order phase transition.In the second case,the critical temperature of deconfinement phase transition and endpoint of RW transition in the high temperature region decrease with the increase of the magnetic field,which is similar to the inverse magnetic catalysis effect of quark condensation.In this case,the RW transition endpoint is still a second-order phase transition.In addition,we also calculated the RW phase diagram and RW endpoint properties under two color flavors,and obtained similar results.Because the improved coupling parameter can give the correct inverse magnetic catalysis effect of quark condensation at high temperature,we expect that the strong external magnetic field can also have the inverse catalysis effect on the change of RW transition endpoint with temperature.This study is a preliminary calculation of related research,which needs lattice QCD and other methods to do further verification.