Dense matter in a holographic hard-wall model of QCD

A deeper understanding of QCD matter at strong coupling remains challenging due to its non-perturbative nature. To this end, we study a two-flavor holographic hard-wall model to investigate the properties of QCD at finite-density and zero temperature with a nonvanishing quark mass. A dense matter phase is described by a classical solution of the equations of motion in a homogeneous Ansatz. We apply holographic renormalization to formulate the holographic dictionary that relates UV boundary data in the bulk with the physical quantities in QCD. We emphasize a role played by an IR boundary action on the hard-wall when analyzing the QCD phase structures in this holographic setup. It is found that a baryonic matter phase is manifested in this model with a high baryon number density and a nearly vanishing chiral condensate. We derive the equation of state for the resulting phase and use it to work out the mass-radius relation for neutron stars. We find that the maximum mass of neutron stars can exceed two solar masses for a wide range of free parameters in this model. We also comment on an alternative scenario about the phase structure such that the baryonic matter phase arises at a baryon number chemical potential greater than a critical value.