Finite Temperature Transition in Two Flavor QCD with Renormalization Group Improved Action

The finite temperature transition or crossover in QCD with two degenerate Wilson quarks is investigated using a renormalization group improved action. At $\beta=2.0$ and 2.1 where $a^{-1} \sim 1.0-1.2$ GeV, the expectation value of the Polyakov loop and the pion screening mass on an $8^3 \times 4$ lattice vary smoothly with the hopping parameter through the transition/crossover. The quark screening mass in the high temperature phase agrees well with that in the low temperature phase calculated on an $8^4$ lattice. The smooth transition of the observables is totally different from the sharp transition found for the standard action at $\beta=5.0$ and 5.1 where $a^{-1}$ is also $1.0-1.2$ GeV.