Chiral transition and meson melting within improved holographic soft wall models

Abstract

We describe the chiral transition for the quark condensate and the melting of scalar and vector mesons in two-flavor holographic quantum chromodynamics (holographic QCD). This is done by extending the improved holographic soft wall models proposed in Ballon-Bayona et al. [Phys. Rev. D 104, 126029 (2021)PRVDAQ2470-001010.1103/PhysRevD.104.126029] to finite temperature, by means of introducing an asymptotically anti-de Sitter black brane. We find that the chiral transition is second order in the chiral limit and a crossover for physical quark masses, as expected in two-flavor QCD. We investigate the melting of vector and scalar mesons in the deconfined plasma through the calculation of hadronic spectral functions. Fixing the model parameters by the meson spectrum at zero temperature, we find that the mesons melt at temperatures between 90 and 110 MeV and the chiral transition occurs around 129 MeV. We also provide a prediction for the hydrodynamic diffusion constant associated with a flavor current in the deconfined plasma.