Finite temperature transitions in lattice QCD with Wilson quarks: chiral transitions and the influence of the strange quark

The nature of finite temperature transitions in lattice QCD with Wilson quarks is studied near the chiral limit for the cases of 2, 3, and 6 flavors of degenerate quarks (N_F=2, 3, and 6) and also for the case of massless up and down quarks and a light strange quark (N_F=2+1). Our simulations mainly performed on lattices with the temporal direction extension N_t=4 indicate that the finite temperature transition in the chiral limit (chiral transition) is continuous for N_F=2, while it is of first order for N_F=3 and 6. We find that the transition is of first order for the case of massless up and down quarks and the physical strange quark where we obtain a value of m_\phi/m_\rho consistent with the physical value. We also discuss the phase structure at zero temperature as well as that at finite temperatures