# QCD in stars

## TL;DR

This paper explores the properties of cold dense QCD in neutron stars, using observational constraints and models to understand phase transitions and the non-perturbative nature of gluons at high densities.

## Contribution

It provides insights into the strength of hadron-quark phase transitions and the persistence of non-perturbative gluons in dense quark matter.

## Key findings

- Neutron star observations constrain phase transition strength.
- Model coupling constants remain large at high densities.
- Gluons stay non-perturbative even after quark matter formation.

## Abstract

We discuss cold dense QCD by examining constraints from neutron stars, nuclear experiments, and QCD calculations at low and high baryon density. The two solar mass constraint and suggestive small radii (10~13 km) of neutron stars constrain the strength of hadron-quark matter phase transitions. Assuming the adiabatic continuity from hadronic to quark matter, we use a schematic quark model for hadron physics and examine the size of medium coupling constants. We find that to baryon density nB ~ 10n0 (n0: nuclear saturation density), the model coupling constants should be as large as in the vacuum, indicating that gluons remain non- perturbative even after the quark matter formation.