The phase boundary for the QCD transition at small chemical potentials

In a recent work [1] we have shown that the curvature of the phase transition line in the chiral limit can be obtained from an analysis of the universal scaling properties of a certain mixed susceptibility (χm,q) which is defined by the leading order Taylor expansion coefficient of the chiral condensate with respect to the light quark chemical potential. Numerical calculations have been performed for (2+1)-flavor QCD keeping the heavier strange quark mass close to its physical value and decreasing the two degenerate light quark masses towards the massless limit. We will make use of a recent scaling analysis [1, 2] of the chiral order parameter performed with an improved staggered fermion action. This study showed that the chiral order parameter is well described by a universal scaling function characteristic for a three dimensional, O(N) universality class. As a result for the critical line in the chiral limit we find