Mapping the boundary of the first order finite temperature restoration of chiral symmetry in the mpi - mK -plane with a linear sigma model
The phase diagram of the three-flavor QCD is mapped out in the low mass corner of the (m(pi)-m(K))-plane with help of the SU(L)(3)xSU(R)(3) linear sigma model (L sigma M). A novel zero temperature parametrization is proposed for the mass dependence of the couplings away from the physical point based on the three-flavor chiral perturbation theory(U(3) ChPT). One-loop thermodynamics is constructed by applying optimized perturbation theory. The unknown dependence of the scalar spectra on the pseudoscalar masses limits the accuracy of the predictions. Results are compared to lattice data and similar investigations with other variants of effective chiral models. The critical value of the pion mass is below 65 MeV for all m(K) value less than or similar to 800 MeV. Along the diagonal m(pi)=m(K), we estimate m(crit)(diag)=40 +/- 20 MeV.