Holographic quarkyonic matter
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Springer
Received: July 1, Revised: August 6, Accepted: August 6, Published: September 17,
2020 2020 2020 2020
Nicolas Kovensky and Andreas Schmitt Mathematical Sciences and STAG Research Centre, University of Southampton, Highfield Campus, Southampton SO17 1BJ, United Kingdom
E-mail: [email protected], [email protected] Abstract: We point out a new configuration in the Witten-Sakai-Sugimoto model, allowing baryons in the pointlike approximation to coexist with fundamental quarks. The resulting phase is a holographic realization of quarkyonic matter, which is predicted to occur in QCD at a large number of colors, and possibly plays a role in real-world QCD as well. We find that holographic quarkyonic matter is chirally symmetric and that, for large baryon chemical potentials, it is energetically preferred over pure nuclear matter and over pure quark matter. The zero-temperature transition from nuclear matter to the quarkyonic phase is of first order in the chiral limit and for a realistic pion mass. For pion masses far beyond the physical point we observe a quark-hadron continuity due to the presence of quarkyonic matter. Keywords: Gauge-gravity correspondence, Phase Diagram of QCD ArXiv ePrint: 2006.13739
c The Authors. Open Access, Article funded by SCOAP3 .
https://doi.org/10.1007/JHEP09(2020)112
JHEP09(2020)112
Holographic quarkyonic matter
Contents 1 Introduction
1 3 3 4 9 11 18
3 Numerical results and discussion 3.1 Quarkyonic matter in the phase diagram 3.2 Baryon fraction in the quarkyonic phase 3.3 Holographic picture of quarkyonic matter 3.4 Quark-hadron continuity
20 21 24 25 27
4 Summary and outlook
31
1
Introduction
The phase structure of Quantum Chromodynamics (QCD) at large, but not asymptotically large, baryon densities is poorly understood. Many candidate phases have been discussed, such as various color superconductors [1], suggested by perturbative results — which are applicable at asymptotically large densities — and by phenomenological models. Another candidate phase is quarkyonic matter, suggested by results for QCD at a large number of colors Nc [2–5]. In this paper we investigate quarkyonic matter in a holographic top-down approach (within a certain approximation). In particular, we determine the phase structure of the model fully dynamically for all temperatures and baryon chemical potentials, i.e., we compare the free energies of quarkyonic matter with those of pure baryonic matter, pure quark matter, and the mesonic phase. There are various ways of characterizing and defining quarkyonic matter, and different studies in the literature focus, sometimes confusingly, on different, often hypothetical, properties of this phase. Originally [2], it was pointed out that the pressure of “large-Nc nuclear matter” scales linearly with Nc , suggesting a bulk contribution of quarks, while confinement indicates that the fermionic excitations of the system are color singlets. Hence the term quarkyonic, suggesting that the phase is partly quark-like, partly baryonic. It was spec
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