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

Understand

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.