Alignment of the QCD phase boundary with chiral and deconfinement transitions

Determine whether the phase boundary separating the quark–gluon plasma and hadronic (confined) phases in the Quantum Chromodynamics (QCD) phase diagram coincides with the chiral transition line and/or the deconfinement transition line across finite baryon chemical potential, to clarify the relationship among these transitions and the existence and location of a critical end point.

Background

A central goal in mapping the QCD phase diagram is to identify the phase boundary between the quark–gluon plasma and confined hadronic matter, especially at finite baryon chemical potential. Lattice results at vanishing chemical potential indicate a crossover transition, while at higher densities a first‑order transition and a critical end point (CEP) are often conjectured.

The review highlights that different theoretical approaches predict differing CEP locations and emphasizes that it remains uncertain whether the thermodynamic phase boundary is aligned with either the chiral restoration line or the deconfinement line. Resolving this question would sharpen the theoretical interpretation of experimental programs at RHIC, FAIR, NICA, SPS, and J‑PARC targeting distinct regions of the phase diagram.