Heavy holographic QCD

Nicolas Kovensky,Andreas Schmitt

doi:10.1007/jhep02(2020)096

Abstract

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.

Highlights

Is not unlike the field-theoretical Nambu-Jona-Lasinio (NJL) model [15, 16], where gluons are completely absent and similar phase structures have been found [17]
The remainder of the paper is devoted to the numerical evaluation of the phases just discussed and to the resulting phase diagrams obtained for different values of the quark mass parameter α and the ’t Hooft coupling λ
We have made use of earlier works that identified the chiral condensate with the expectation value of a non-local, gauge-invariant open Wilson line operator

Summary

Introduction

Is not unlike the field-theoretical Nambu-Jona-Lasinio (NJL) model [15, 16], where gluons are completely absent and similar phase structures have been found [17]. The expectation value of this operator is comparable — but due to its nonlocal nature not identical — to the usual chiral condensate While this expectation value was calculated and discussed in previous works, it has, to the best of our knowledge, not yet been implemented into a fully consistent calculation of the phase structure, which includes its backreaction on the embedding of the flavor branes. We provide such a calculation for nonzero temperatures and chemical potentials.

Objectives

Results

Conclusion