From holography towards real-world nuclear matter

TL;DR

This paper explores dense nuclear matter using the holographic Sakai-Sugimoto model, aiming to capture key phase transitions relevant for astrophysics across a wide density range with minimal parameters.

Contribution

It introduces a holographic approach to model cold, dense matter across various densities, analyzing two approximations to improve realism in describing nuclear and quark matter phases.

Findings

Instanton gas shows chiral restoration at high density

Homogeneous ansatz predicts a first-order baryon onset

Model provides a foundation for more realistic equations of state

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.