# Cool baryon and quark matter in holographic QCD

## TL;DR

This paper develops a holographic QCD model that captures both baryonic and quark matter phases at low temperature and high density, revealing phase transitions and a stiff equation of state.

## Contribution

It introduces a bottom-up holographic model incorporating baryons and quark matter with backreaction, providing new insights into dense QCD phases.

## Key findings

- Identifies first-order phase transitions between vacuum, baryon, and quark matter.
- Shows the baryonic phase has a stiff equation of state with high speed of sound.
- Finds the second baryon modeling approach aligns well with phenomenological expectations.

## 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 $c_s^2=1/3$ of conformal plasmas at high baryon densities.