QCD Phase Transition And Energy Loss From Holographic Approach

The investigation on the phase structure of QCD and nature of QGP always are the important topics of high-energy physics.We use AdS/CFT to study the strong coupling problem of QCD since the perturbative method is not applicable in the low energy range.AdS/CFT provides a new idea to study strong coupling problems through weak coupling theory of gravity and gradually becomes a powerful tool to study non-perturbative problems.In this thesis,we study the QCD phase structure and the energy loss near the phase transition temperature by using the holographic QCD.Firstly,we improve the holographic Eeinstein-Maxwell-Dilaton(EMD)model for light quarks with nonzero magnetic field and chemical potential.It has been verified that the gravity metric solutions are self-consistent and reliable.Then we study the phase diagram in T-μ and T-B planes and discuss the effects of magnetic field and chemical potential on the critical endpoints.We observe the magnetic field reduces phase transition temperature,namely inverse magnetic catalysis(IMC),which is consistent with the lattice results.We also observe that magnetic field increases the critical μCEP and chemical potential enhances the critical BCEP.We find the equations of state(EoS)near the phase transition temperature are non-monotonic.Moreover,we find that the drag force of heavy quark andjet quenching parameter show an enhancement near the phase transition temperature from the results of energy loss.The peak values of drag force and q are pushed towards lower temperature when increasing B or μ.This phenomenon is consistent with the observation that the phase transition temperature decreases with increasing B or μ in this holographic model.When perpendicular to magnetic field,we find drag force is bigger than that for the parallel case f⊥>f‖ which is consistent with the results of jet quenching parameter q⊥>q‖.Furthermore,we improve the holographic EMD model for heavy quarks in different dimensions and study the phase diagram for heavy quarks in this model.We discuss the equations of state and heavy quark energy loss near the phase transition temperature in different dimensions.We find some common conclusions by comparing the results of model for light quarks.The thermodynamics of the system changes continuously and rapidly near the crossover temperature while are non-monotonic near the first-order phase transition temperature.The energy loss behaves an enhancement near the phase transition temperature characterizing the phase transition in some sense.Moreover,we study the phase diagram in T-μ and T-ωL planes since the nonzero total angular momentum produced from the non-central heavy ion collisions.We discuss the effects of angular velocity and chemical potential on the critical endpoints.We find the angular velocity decreases the deconfinement phase transition temperature and the criticalμCEP.Then we calculate the EoS in the rotating background.Finally,we study the generation of gravitational waves(GWs)from the early universe QCD phase transition by using holographic method.We discuss the effect of gluon condensate on the confinement-deconfinement phase transition.Then we study the effect of gluon condensate on the peak frequency and energy density of total GWs.