Strangeness neutrality and the QCD phase diagram

TL;DR

This paper maps the QCD phase diagram at strangeness neutrality using functional QCD, identifying a critical end point and validating results against lattice QCD and previous studies.

Contribution

It provides a systematic, improved functional QCD analysis of the phase structure at strangeness neutrality, including the critical end point location.

Findings

Critical end point at (92, 696) MeV in temperature and baryon chemical potential.

Results agree with lattice QCD at zero chemical potential.

The ratio of curvature coefficients matches lattice results.

Abstract

We map out the phase structure of $N_f=2+1$ flavour QCD at strangeness neutrality with functional QCD. We find a critical end point at $(T_{\rm CEP},\mu_{B,{\rm CEP}})|_{n_S=0} = (92, 696)$\,MeV. The computation is done with the functional renormalisation group, and we systematically improve on previous works, hence reducing the systematic error significantly. Our results pass relevant QCD benchmarks: they agree well with and corroborate the QCD phase structure from functional QCD results at vanishing strangeness chemical potential. Moreover, they agree well with lattice QCD results at vanishing chemical potential. Specifically, the ratio of the second order curvature coefficient $\kappa_2$ agrees with that obtained from lattice computations, $\kappa_2(n_S=0)/\kappa_2(\mu_S=0)=0.897(20)$.