The phase diagram of QCD at small chemical potentials

TL;DR

This paper explores the phase diagram of QCD at small chemical potentials, focusing on chiral symmetry restoration and pion condensation, and extends previous symmetry-based analyses to the realistic case of broken flavor symmetry.

Contribution

It provides a unique extension of the phase diagram topology to fully broken flavor symmetry and constrains possible phase diagrams in three-flavor QCD using lattice data.

Findings

Chiral symmetry restoration and pion condensation are key features at small chemical potentials.

The extension of phase diagram topology to broken flavor symmetry is unique.

Lattice data restricts three-flavor QCD phase diagrams to two main scenarios.

Abstract

We investigate the phase diagram of QCD at small chemical potentials, ie, when chiral and flavour symmetry breaking involves the pairing of a quark and an antiquark. The phase diagram of two-flavour QCD at small chemical potentials involves chiral symmetry restoration and charged pion condensation. We extend previous studies of the topology of the phase diagram, in sections with high degree of symmetry, to the physical case of fully broken flavour symmetry, using generic thermodynamic arguments. We argue that the extension is unique and present the result. In three flavour QCD the phase diagram for chiral symmetry restoration is less well constrained. However, we argue that present lattice data allows just two different phase diagrams, which we discuss.