Abstract
We establish a holographic bottom-up model which covers both the baryonic and quark matter phases in cold and dense QCD. This is obtained by including the baryons using simple approximation schemes in the V-QCD model, which also includes the backreaction of the quark matter to the dynamics of pure Yang-Mills. We examine two approaches for homogeneous baryon matter: baryons as a thin layer of noninteracting matter in the holographic bulk, and baryons with a homogeneous bulk gauge field. We find that the second approach exhibits phenomenologically reasonable features. At zero temperature, the vacuum, baryon, and quark matter phases are separated by strongly first order transitions as the chemical potential varies. The equation of state in the baryonic phase is found to be stiff, i.e., the speed of sound clearly exceeds the value cs2 = 1/3 of conformal plasmas at high baryon densities.
Highlights
Densities where reliable and accurate approaches are not available
V-QCD is a class of holographic models for QCD, obtained through a fusion [7] of two frameworks: improved holographic QCD (IHQCD) [8,9,10,11,12] for the gluon sector, and a setup based on Sen-like tachyonic Dirac-Born-Infeld (DBI) actions for the quark sector [13, 14]
We explored how baryonic physics can be included in the V-QCD model
Summary
We start by reviewing the two basic building blocks of V-QCD. First, improved holographic QCD [8,9,10,11,12] gives the description of the dynamics of gluons. To set the best boundary conditions for the IR physics, we choose the UV behavior of the functions to agree with QCD perturbation theory: as usual we require that the correct UV dimensions of the various operators are reproduced, but in addition we require agreement with asymptotic freedom [8, 9], with RG flow of the quark mass [7], and behavior at large quark mass [57]. This is obtained if all the functions go to constants in the UV with perturbative corrections in λ. The explicit choices of potentials which we use in this article are given in appendix B
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