Critical point in the chiral phase diagram of soft-wall holographic QCD*

The search for the expected critical point of the nuclear phase diagram is an ongoing theoretical and experimental project. While lattice QCD methods predict a rapid crossover at zero baryon chemical potential, extending these methods to finite chemical potential remains a challenge. So far, such efforts have not shown the presence of a critical point. We contribute to this project using holographic QCD, a phenomenological application of the AdS/CFT correspondence. We focus on the chiral phase boundary between ordinary nuclear matter and the quark-gluon plasma, as indicated by the restoration of chiral symmetry.

In the soft-wall holographic model, confinement is introduced by a dilaton field. While the minimal soft-wall models do not exhibit a critical point in the chiral phase diagram, introducing a coupling between the dilaton and the scalar dilaton field introduces a critical point. We examine the effect of the scalar-dilaton coupling on the existence and location of the critical point. We also study the zero-temperature chiral dynamics, which must allow for spontaneous chiral symmetry breaking in the limit of zero quark mass. We find that when the scalar-dilaton coupling is large enough to ensure correct zero-temperature chiral dynamics, a critical point is present only if the quark mass is greater than 12.8 MeV in a flavor-symmetric model.