QCD Phase Structure

QCD Phase Structure

Phase structure of QCD at finite temperature is studied for 2+1 flavor theory (including up, down and strange-quarks). Convensional simulations using lattice discretization methods which do not appreciate the symmetry of the nature lead to a conclusion that the stransition is crossover without having no jump in the physical observables. On the other hand, we do not have a concrete numerical prediction on the phase near chiral limit of degenerate two and three flavor theories which are thought to have better understanding from theoretical investigations. Indeed, in the study of two flavor theory performed under the post-K priority issue #9, we observed rapid change like a jump in the physical observables that have not been known before. This seems to be an effect accompanying with the restoration of the anomalous U(1) symmetry, which has unfolded first time in this study utilizing a chirally symmetric formulation of lattice QCD. In this project,phase structure of more realistic 2+1 flavor theory is investigated through the simulations at several values of temperature, using the lattice formulation that preserves the chirally symmetry and the existence/absence of the (pseudo) phase transition is examined.