The boundary of the first order chiral phase transition in the mπ−mK-plane with a linear sigma model

Tree-level and complete one-loop parametrisation of the linear sigma model (LσM) is performed and the phase boundary between first order and crossover transition regions of the mπ−mK-plane is determined using the optimised perturbation theory (OPT) as a resummation tool of perturbative series. Away from the physical point the parameters of the model were determined by making use of chiral perturbation theory (ChPT). The location of the phase boundary for mπ=mK and of the tricritical point (TCP) on the mπ=0 were estimated.