From holography towards real-world nuclear matter

Abstract

Quantum chromodynamics is notoriously difficult to solve at nonzero baryon density, and most models or effective theories of dense quark or nuclear matter are restricted to a particular density regime and/or a particular form of matter. Here we study dense (and mostly cold) matter within the holographic Sakai-Sugimoto model, aiming at a strong-coupling framework in the wide density range between nuclear saturation density and ultra-high quark matter densities. The model contains only three parameters, and we ask whether it fulfills two basic requirements of real-world cold and dense matter, a first-order onset of nuclear matter and a chiral phase transition at high density to quark matter. Such a model would be extremely useful for astrophysical applications because it would provide a single equation of state for all densities relevant in a compact star. Our calculations are based on two approximations for baryonic matter, firstly an instanton gas and secondly a homogeneous ansatz for the non-abelian gauge fields on the flavor branes of the model. While the instanton gas shows chiral restoration at high densities but an unrealistic second-order baryon onset, the homogeneous ansatz behaves exactly the other way around. Our study thus provides all ingredients that are necessary for a more realistic model and allows for systematic improvements of the applied approximations.Comment: 31 pages, 7 figures, v2: references added, version to appear in Physical Review

Breaking the sound barrier in holography

“…In this context, a highly promising avenue is the application of the holographic duality [8], which has indeed been lately applied to the description of both the nuclear [9][10][11][12][13][14][15][16] and quark matter [17][18][19] phases inside a neutron star.…”

Quark Matter Equation of State from Perturbative QCD

“…With lattice QCD suffering from the infamous Sign Problem [3] and the applicability of Chiral Effective Theory (CET) extending only up to roughly the nuclear matter saturation density [4], there is an urgent need to find complementary methods for tackling strongly coupled matter at the the highest densities reached within the stars. This has motivated attempts to approach the problem using methods ranging from the Functional Renormalization Group to phenomenological models and the holographic duality [5][6][7][8][9][10], but they all come with their own systematic uncertainties and limitations.…”

Baryon superfluids in AdS/CFT with flavor

“…In order to describe baryonic matter one needs to study multi-soliton solutions [16][17][18][19] or use a phenomenological approach if one is interested in homogeneous states [20][21][22][23][24][25][26][27][28][29], with the drawback that the physical properties of the state depends on the assumptions one needs to make. Furthermore, stable soliton solutions have sizes that are typically of the order of the string scale [14], thus casting doubts on the validity of the brane action used to find those solutions.…”