Chiral critical point and meson melting in an improved holographic QCD model

We present an improved holographic QCD model that exhibits a critical point in the phase boundary between hadronic matter and chirally symmetric quark-gluon plasma. The soft-wall holographic QCD framework introduces confinement via a dilaton field and reproduces key features of QCD, including light meson spectra. Chiral symmetry breaking is described by a scalar field dual to the chiral condensate, which vanishes at high temperatures and chemical potentials, indicating the restoration of chiral symmetry.

We build on our previous work that produces a critical end point in the chiral phase diagram via a coupling between the chiral and dilaton fields. We analyze the behavior of the ρ and a₁ mesons, chiral partners that become degenerate with the restoration of chiral symmetry. By examining the Schrödinger-like potential in the meson equations of motion, we can determine a melting point where bound states are no longer expected. We compare the "melting lines" for these two sectors of mesons to the chiral phase boundary. At low chemical potential, degeneracy of chiral partners can occur before melting, depending on the chiral-dilaton coupling parameter. At high chemical potential, bound states vanish before chiral symmetry is restored.