  We study the phase structure of the Witten-Sakai-Sugimoto model in the plane
of temperature and baryon chemical potential, including the effect of a nonzero
current quark mass. Our study is performed in the decompactified limit of the
model, which, at least regarding the chiral phase transition, appears to be
closer to real-world QCD than the original version. Following earlier studies,
we account for the quark mass in an effective way based on an open Wilson line
operator whose expectation value is identified with the chiral condensate. We
find that the quark mass stabilizes a configuration with string sources and
point out that this phase plays an important role in the phase diagram.
Furthermore, we show that the quark mass breaks up the first-order chiral phase
transition curve and introduces critical points to the phase diagram.
Similarities of the phase structure to other holographic approaches and to
lattice simulations of "heavy QCD" are found and discussed. By making
holographic QCD more realistic, our results open the door to a better
understanding of real-world strongly coupled hot and dense matter.
