Chiral Phase Transition In U(2)×U(2) Linear Sigma Model Under Magnetic Field

The phase transition of matter is a very important topic in physics, it produces very richphenomena and is applied widely. Phase transition exists not only in condensed physics, butalso in nuclear physics and particle physics. The phase transition from hadron phase toquark-gluon plasma phase is the research object in particle physics, which relates with theevolution of cosmos intimately and stands on the frontier of particle physics. Therefore it issignificant to investigate phase transition in particle physics.Important phase transition phenomena in particle physics include deconfinement phasetransition, chiral phase transition and color superconducting phase transition. On the one hand,the thermal motion of quarks and gluons in hadrons will become stronger with increasingtemperature, or the boundary of individual hadron will become obscure or even vanish whenthe hadrons are under great pressure, then deconfinement phase transition happens. Thus,hadrons in confinement become quark gluon plasma. On the other hand, the stronger thermalmotion will break quark condensation and leads to chiral phase transition. The color superductphase transition is similar to the electric one in electromagnetism. However, it becomes morecomplicated because the nonabelian property of QCD. Moreover, one finds the complicationin QCD phase transition arises not only from the nonperturbative nature of QCD but also themore degrees of freedom, different flavor number or different masses of quarks will changephase transition behavior obviously.Quantum Chromodynamics at finite temperature is the fundamental theory in researchinghadron phase transition. But similar to the situation at zero temperature, the confinementnature of strong interaction makes very great difficulty. Therefore effective theories becomeone of the important method. Models such as the chiral perturbative theory, linear sigmamodels and NJL models are used extensively in QCD phase transition research.Recently, QCD phase transition in external magnetic background is discussed intensely,because QCD phase transition happens in magnetic background not only in quark stars butalso in heavy ion collision.In this thesis we investigate chiral phase transition under uniform magnetic field byusing U(2)×U(2) linear sigma model. In our research, we use effective potential method,discuss one-loop effective potential with different temperatrure, baryonic chemical potentialand magnetic field magnitude in order to investigate phase transition types. We find critical temperature increases with increasing magnetic field intensity; meson degrees of freedomhave little influence and vaccum flacutation can change phase transition types.