The vicinity of a critical end point is analyzed in order to reveal singularities arising in the form of the first-order phase boundary to the noncritical phase. Phenomenological arguments are presented and critically assessed that directly relate the nonanalytic behavior of the phase boundary to universal features of the bulk thermodynamics on the associated critical line. Explicit values are given for universal amplitude ratios describing the boundary for various types of criticality.

• Received 18 October 1990

DOI:https://doi.org/10.1103/PhysRevB.43.11177