The equation of state in two-, three-, and four-color QCD at non-zero temperature and density

TL;DR

This paper computes the equation of state for various QCD-like theories at non-zero temperature and density, matching low-energy hadron models with high-energy perturbative results, and makes predictions testable by lattice studies.

Contribution

It provides the first-principles calculation of the QCD equation of state across different color numbers and fermion representations, extending lattice results and offering new predictions.

Findings

Quantitative agreement with lattice QCD at zero chemical potential for three colors.

Predictions for the equation of state in two- and four-color QCD at non-zero chemical potential.

Speed of sound squared can exceed one third at zero temperature, relevant for neutron star physics.

Abstract

We calculate the equation of state at non-zero temperature and density from first principles in two-, three- and four-color QCD with two fermion flavors in the fundamental and two-index, antisymmetric representation. By matching low-energy results (from a `hadron resonance gas') to high-energy results from (resummed) perturbative QCD, we obtain results for the pressure and trace anomaly that are in quantitative agreement with full lattice-QCD studies for three colors at zero chemical potential. Our results for non-zero chemical potential at zero temperature constitute predictions for the equation of state in QCD-like theories that can be tested by traditional lattice studies for two-color QCD with two fundamental fermions and four-color QCD with two two-index, antisymmetric fermions. We find that the speed of sound squared at zero temperature can exceed one third, which may be relevant for the phenomenology of high-mass neutron stars.